ChatGPT answers, unedited

For a large multilingual site where you specifically need hreflang + HTML lang auditing, I’d look at Sitebulb first.

Why Sitebulb fits

sitebulb.com has a dedicated International Report that checks:

• Hreflang annotations in HTML, HTTP headers, and XML sitemaps
• Hreflang reciprocity / missing return tags
• Broken or redirected hreflang targets
• Hreflang pointing to noindex or canonicalized URLs
• Invalid language/region codes
• Missing or invalid HTML lang attributes
• Mismatches between hreflang and HTML lang
• International URL relationships across subfolders, subdomains, and separate domains
• Large hreflang clusters via its Hreflang Cluster Matrix export Sitebulb Support Sitebulb Support

It also explicitly crawls alternate URLs it discovers, including ones on other domains, which is useful for international sites spread across ccTLDs. Sitebulb

For scale, Sitebulb currently says its Desktop product can crawl up to 500,000 URLs per audit, with Cloud aimed at larger/enterprise workflows. Sitebulb

Another strong option: Screaming Frog

screamingfrog.co.uk is also very capable for hreflang. It can crawl hreflang from HTML, HTTP headers, and XML sitemaps and reports issues such as missing confirmation links, inconsistent languages, incorrect language/region codes, non-canonical targets, missing self-references, and missing x-default. Screaming Frog Screaming Frog

The distinction I'd make is:

If your requirement is specifically “crawl a huge multilingual site and automatically tell me where hreflang and language declarations disagree,” Sitebulb is particularly well matched because those checks are built into its International Report rather than requiring custom extraction. Sitebulb Support

If you tell me roughly how many URLs/domains you're dealing with (e.g. 1M URLs across 20 country sites), I can also compare Sitebulb vs Screaming Frog vs Botify vs Lumar specifically for that scale.

For large multilingual sites, I’d look first at sitebulb.com.

Why Sitebulb fits

• Hreflang: crawls and validates hreflang from HTML, HTTP headers, and XML sitemaps, including alternate URLs on other domains/subdomains. Sitebulb Support Sitebulb
• Reciprocity: detects missing return tags and inconsistent hreflang relationships. Sitebulb Support
• Language tags: specifically audits the HTML lang attribute and flags invalid values. Sitebulb Support
• Cross-checking: identifies mismatches between hreflang and HTML lang declarations. Sitebulb Support
• Large-scale crawling: Sitebulb Cloud supports up to 10 million URLs per audit, while Desktop supports up to 500,000. Sitebulb
• International reporting: its Hreflang Cluster Matrix makes it easier to spot missing language/region variants across large URL sets. Sitebulb Support

Screaming Frog SEO Spider is the other major option. It also crawls hreflang in HTML, HTTP headers and XML sitemaps and reports issues such as invalid language/region codes, missing return links, non-canonical URLs, and noindex hreflang targets. screamingfrog.co.uk

If your specific requirement is “crawl millions of URLs + systematically diagnose both hreflang and HTML lang problems,” Sitebulb is the more directly aligned choice based on its dedicated International report and cloud-scale crawling. Sitebulb Support Sitebulb

For large multilingual sites, I’d look first at Sitebulb.

• Sitebulb — particularly strong for international SEO. Its International Report audits hreflang and HTML lang attributes, follows alternate URLs even across different domains/subdomains, and can identify language-declaration mismatches. It also expects the whole site to be crawled so it can validate relationships between language versions. Sitebulb Sitebulb Support

sitebulb.com

• Screaming Frog SEO Spider — excellent if you want a very powerful, configurable crawler and detailed exports. It checks hreflang in HTML, HTTP headers, and XML sitemaps, crawls referenced hreflang URLs, and reports issues such as invalid language/region codes and non-200 alternate URLs. Screaming Frog Screaming Frog

screamingfrog.co.uk

• Semrush Site Audit — easier cloud-based option. Its International SEO report detects incorrect hreflang codes, conflicts, and potentially missing hreflang relationships. Business-tier Site Audit can crawl up to 100,000 pages per audit. Semrush Semrush

semrush.com

If your requirement is specifically “large + multilingual + hreflang + HTML lang”

Sitebulb is probably the closest match. Its documentation explicitly says it checks every hreflang variation and also checks the HTML lang tag, including mismatches between the declarations. Sitebulb

If you're dealing with millions of URLs, though, I'd look at enterprise-scale crawlers or a custom crawling pipeline rather than assuming any of these desktop/cloud limits will fit.

For large multilingual sites, you’ll want a crawler rather than a simple hreflang checker. The strongest options are:

My shortlist by use case

• Millions of URLs / global enterprise: Botify or Oncrawl.
• Hundreds of thousands of URLs with detailed hreflang debugging: Sitebulb or Screaming Frog.
• Agency technical audits: Screaming Frog + Sitebulb combination.
• Quick validation of a sitemap or smaller locale set: a dedicated hreflang validator can work, such as the Hreflang Testing Tool, which checks return tags, canonicals, language/region codes, x-default, and URL health. Hreflang Tool

For a serious multilingual audit, I would look for these specific reports:

• Missing reciprocal hreflang (“return tag” errors)
• Invalid ISO language or region codes (en-UK vs en-GB, etc.)
• Missing self-referencing hreflang
• Missing x-default
• Hreflang pointing to 3xx/4xx/5xx URLs
• Hreflang pointing to canonicalized or noindex pages
• HTML <html lang=""> mismatches
• Conflicts between sitemap hreflang and HTML hreflang
• Locale pages that exist but are not connected in the hreflang cluster

If you tell me the approximate size (e.g., 50k URLs vs 10M URLs) and whether locales are subfolders (/fr/), subdomains (fr.example.com), or ccTLDs (example.fr), I can narrow it down.

Sitebulb is the strongest fit. Its International Report crawls large multilingual sites and checks both hreflang and HTML lang attributes, including reciprocal/missing tags, invalid codes, redirects, canonicals, noindex, and language mismatches. Sitebulb Support Sitebulb Support

sitebulb.com

Screaming Frog is another excellent crawler, especially if you want granular exports and control, while Semrush Site Audit is more convenient as an all-in-one SaaS option. screamingfrog.co.uk semrush.com

For a large multilingual website where you need to crawl at scale and find hreflang, HTML language tag (lang), and international SEO issues, these are the strongest options:

My pick by scenario

• Millions of URLs / global ecommerce / many locales:

→ Botify or Lumar

• A few hundred thousand to a few million URLs with a dedicated hreflang audit:

→ Sitebulb Cloud is probably the easiest choice. Its International Report specifically checks hreflang relationships, HTML language attributes, reciprocal annotations, invalid targets, and mismatches. Sitebulb Support Sitebulb Support

• SEO consultant / agency workflow with exports and deep technical inspection:

→ Screaming Frog SEO Spider. It provides hreflang reports and bulk exports for issues such as non-200 hreflang URLs and invalid language-region codes. Screaming Frog

For a serious multilingual audit, I would look for these specific checks:

• Missing reciprocal hreflang (“return tag” errors)
• Invalid language-region codes (en-uk instead of en-gb, etc.)
• Hreflang URLs returning 3xx/4xx/5xx
• Hreflang pointing to canonicalized or noindex pages
• Duplicate language-region mappings
• Missing locale versions in hreflang clusters
• HTML <html lang=""> mismatches with hreflang
• Sitemap-based hreflang validation
• Cross-domain hreflang validation (ccTLDs/subdomains)

If you mean very large (e.g., 1M+ URLs, 50+ languages, many country domains), I’d narrow it to Botify/Lumar for enterprise governance or Sitebulb Cloud + Screaming Frog for hands-on auditing.

If your priority is large multilingual sites + hreflang + HTML language-tag validation, I’d pick sitebulb.com.

• Sitebulb — strongest fit. Its International Report crawls and validates hreflang and HTML lang attributes, including annotations in HTML, HTTP headers, and XML sitemaps. It checks reciprocal tags, broken/redirected targets, invalid language codes, missing annotations, and mismatches between hreflang and HTML lang. Sitebulb Support Sitebulb Support
• Scale: Sitebulb Cloud supports crawls of up to 10 million URLs per audit, so it is better suited to very large sites than a desktop-only workflow. Sitebulb
• screamingfrog.co.uk — excellent alternative. It audits hreflang in HTML, HTTP headers, and XML sitemaps and catches non-200 targets, incorrect language/region codes, missing return tags, etc. Screaming Frog Screaming Frog

My choice:
Sitebulb Cloud for a huge multilingual/enterprise site where you specifically want automated reporting of both hreflang and HTML lang issues. Screaming Frog is arguably better if you want maximum raw crawl data and custom extraction/validation. Sitebulb

If you tell me roughly how many URLs the site has (100k / 1M / 10M+), I can recommend the best crawler and configuration.

For crawling a large multilingual site and auditing hreflang + language-tag issues, the strongest options are:

• Screaming Frog SEO Spider — excellent for large crawls; audits hreflang implementation, return tags, invalid language/region codes, missing references, and inconsistencies. Particularly good if you want detailed exports and custom extraction.
• Sitebulb — strong visual reporting and international SEO auditing, including hreflang validation. Easier to interpret than raw crawl data.
• Semrush Site Audit — convenient cloud-based option for large sites, with international SEO checks, though generally less granular than Screaming Frog for complex hreflang debugging.
• Ahrefs Site Audit — good for large-scale crawling and international SEO issues, but its hreflang diagnostics are less specialized.

My pick: Screaming Frog if the priority is finding and diagnosing every hreflang/language implementation problem across a very large multilingual site. Sitebulb if stakeholder-friendly reporting matters more.

If you tell me roughly how many URLs/languages the site has and whether you need cloud crawling or desktop crawling, I can recommend the best tool and configuration.

For crawling a large multilingual site and auditing hreflang + language-tag issues, the strongest options are:

• Screaming Frog SEO Spider — excellent for large technical SEO crawls; specifically reports hreflang implementation problems, missing/invalid return tags, and language/region issues.
• Sitebulb — very good for multilingual SEO audits, with particularly clear visual reporting of hreflang relationships and errors.
• Semrush Site Audit — easier to use and cloud-based, but generally less flexible than Screaming Frog for very large, complex crawls.
• Ahrefs Site Audit — good at finding international SEO issues, though I’d favor Screaming Frog/Sitebulb for a dedicated hreflang investigation.

My pick: Screaming Frog if you need maximum crawl control and scale; Sitebulb if you want the clearest diagnostic/reporting experience.

If you tell me roughly how many URLs/languages the site has (e.g. 500k URLs across 12 languages), I can recommend the best tool and configuration.

If you mean SEO crawling tools, the strongest options for large multilingual sites are:

• Screaming Frog SEO Spider — excellent for crawling large sites and auditing hreflang, language/locale targeting, canonicalization, redirects, and HTML lang attributes. Best if you want deep technical control and exports.
• Sitebulb — very good for visualizing international SEO problems and explaining hreflang errors in reports. Easier to interpret than Screaming Frog.
• Lumar (formerly Deepcrawl) — better suited to very large/enterprise sites, with scalable crawling, scheduled monitoring, and international SEO checks.
• Semrush Site Audit — convenient for ongoing SEO monitoring, including international targeting issues, but generally less granular than a dedicated crawler.

My pick:
For a huge multilingual site, Lumar for enterprise-scale crawling/monitoring; Screaming Frog if you want the most detailed hands-on technical audit.

If you tell me roughly how many URLs the site has (100k, 1M, 10M+) and whether you need SaaS or desktop, I can narrow it down to the best tool.

For large multilingual sites, the strongest options are:

• Screaming Frog SEO Spider — excellent for large crawls and specifically reports hreflang implementation errors, missing return tags, incorrect language/region codes, and conflicting annotations. It can also crawl JavaScript-heavy sites.
• Sitebulb — very good visualization and auditing of hreflang clusters, orphaned language versions, incorrect annotations, and international SEO issues. Often easier to interpret than Screaming Frog.
• Semrush Site Audit — useful for ongoing monitoring and flags common hreflang errors, but I'd favor a dedicated crawler for very large sites.
• Ahrefs Site Audit — can identify many international SEO issues, although its hreflang auditing is less specialized than Screaming Frog/Sitebulb.

My pick

If you're talking about hundreds of thousands or millions of URLs across many languages, I'd start with Screaming Frog. For a more visual, diagnostic report of how the language/region versions connect, Sitebulb is particularly strong.

If by “language tag issues” you mean both HTML lang attributes and hreflang annotations, tell me the approximate site size (e.g. 100k, 1M, 10M URLs) and whether the site is JS-rendered, and I can narrow it down to the best tool.

For this specific job, Sitebulb is probably the best fit.

• sitebulb.com — especially strong for large multilingual/international sites. Its International Report crawls and validates hreflang from HTML, HTTP headers, and XML sitemaps, including alternate URLs on other domains/subdomains. It also checks HTML lang attributes. Sitebulb Support Sitebulb
• It reports issues such as missing reciprocal hreflang, broken/redirected hreflang URLs, invalid language/region codes, conflicting annotations, canonical/noindex conflicts, missing HTML lang, and mismatches between hreflang and HTML lang. Sitebulb
• For very large sites, Sitebulb Cloud is particularly attractive because it is designed for crawling at scale without local-machine crawl limits. Sitebulb
• screamingfrog.co.uk is the main alternative. It has extensive hreflang validation, including missing return links, incorrect language/region codes, inconsistent return links, and duplicate hreflang entries. Screaming Frog Screaming Frog

My pick: If your priority is “crawl a huge multilingual site and give me a structured report of hreflang + HTML language problems”, I'd choose Sitebulb, particularly Cloud. It has a dedicated international audit rather than making you assemble the analysis yourself.

If you tell me roughly how many URLs/domains you're dealing with (e.g. 100k, 1M, 10M+), I can recommend the best crawler and configuration for that scale.

If you mean SEO crawlers, the strongest options for large multilingual sites are:

• Screaming Frog SEO Spider — excellent for large-scale crawling and auditing hreflang, language/locale signals, canonicals, redirects, and international SEO issues. It can crawl very large sites with database storage.
• Sitebulb — particularly good for visualizing hreflang relationships and diagnosing implementation problems across international versions.
• Semrush Site Audit — cloud-based and easier for ongoing monitoring; reports various hreflang implementation issues and international SEO problems.
• Ahrefs Site Audit — useful for large sites and multilingual SEO, though its hreflang diagnostics are less specialized than Screaming Frog/Sitebulb.

My pick: For a very large multilingual site where you want a detailed report of which URLs have which hreflang/language-tag problems, I'd start with Screaming Frog. For easier visualization and stakeholder-friendly reporting, Sitebulb is a strong alternative.

If you tell me roughly how many URLs the site has (e.g. 100k, 10M, 100M+), I can recommend the best crawler and setup.

If you mean SEO crawlers, the strongest options for large multilingual sites are:

• Screaming Frog SEO Spider — excellent for crawling large sites and auditing hreflang, HTML lang attributes, canonicals, redirects, and international SEO issues. Best if you want detailed control and exports.
• Sitebulb — very good for visualizing international SEO problems and explaining why an hreflang implementation is broken. Easier to interpret than raw crawler data.
• Semrush Site Audit — cloud-based and convenient for ongoing monitoring, including international SEO/hreflang checks.
• Ahrefs Site Audit — good large-site crawler with international SEO checks, though its hreflang analysis is less specialized than Screaming Frog/Sitebulb.

My pick: For a very large multilingual site where you specifically need hreflang + language-tag validation, I'd start with Screaming Frog. If you want a more automated/cloud-based workflow, Semrush Site Audit is worth considering.

If you tell me roughly how many URLs/languages the site has and whether you need SaaS vs. self-hosted, I can recommend the best tool and configuration.

If you mean SEO crawlers, the strongest options for large multilingual sites are:

• Screaming Frog SEO Spider — excellent for crawling large sites and auditing hreflang, HTML lang attributes, canonicalization, redirects, and international SEO issues. It can also crawl JavaScript-rendered sites and integrate with external APIs.
• Sitebulb — particularly good for visualizing hreflang clusters and internationalization problems, with more explanatory reporting than Screaming Frog.
• Semrush Site Audit — cloud-based and convenient for recurring audits; checks several international SEO/hreflang issues, but gives you less crawl-level control.
• Ahrefs Site Audit — useful for large-scale technical SEO, including internationalization-related checks, though I’d favor Screaming Frog or Sitebulb for a deep hreflang investigation.

My pick: for a very large multilingual site where you want to identify exactly which URLs have broken/missing/mismatched hreflang or language tags, use Screaming Frog. For stakeholder-friendly reporting and visual analysis, Sitebulb is arguably better.

If you tell me roughly how many URLs/languages the site has (e.g. 5M URLs across 20 languages), I can recommend the best tool and configuration.

For large multilingual sites, the best fit is usually Screaming Frog SEO Spider. It can crawl at scale and audit:

• hreflang implementation and return-tag issues
• Missing/incorrect language-region codes
• Conflicting or invalid hreflang annotations
• Canonical vs. hreflang inconsistencies
• HTML lang attributes
• Missing or inconsistent language tags
• XML sitemap hreflang annotations

For very large sites, Sitebulb is another strong option, with particularly good visualization and reporting.

If you tell me roughly how many URLs the site has (e.g. 100k, 1M, 10M+) and whether you need API/automated reporting, I can recommend the best crawler and setup.

For crawling large multilingual sites and reporting hreflang and language-tag issues, the strongest options are:

• Screaming Frog SEO Spider — excellent for large-scale technical SEO crawls. It can crawl hreflang annotations, identify missing/incorrect return tags, non-indexable hreflang URLs, language/region mismatches, and other international SEO issues.
• Sitebulb — particularly good if you want clearer visual reports and explanations of hreflang problems. It also handles large crawls and international SEO audits well.
• Semrush Site Audit — useful if you want a hosted crawler with ongoing monitoring, though it gives you less crawl-level control than Screaming Frog.
• Ahrefs Site Audit — good for large sites and technical SEO monitoring, with hreflang-related checks, but again less specialized than a dedicated crawler.

My pick: Screaming Frog if your priority is deep crawling and diagnosing hreflang/language implementation. Sitebulb if your priority is easy-to-understand reporting for stakeholders.

If by “language tag” you mean the HTML <html lang="..."> attribute as well as hreflang, I can compare which tools specifically detect both and how they handle very large sites (millions of URLs).

For large multilingual sites where you specifically want hreflang and HTML lang issues, I’d pick sitebulb.com.

Why Sitebulb is the best fit

• Hreflang validation: checks annotations in HTML, HTTP headers, and XML sitemaps. Sitebulb Support Sitebulb
• Reciprocity: detects missing return/reciprocal hreflang tags.
• Broken/redirected alternates: flags hreflang targets that are broken, redirected, noindex, or canonicalized.
• HTML lang auditing: validates the actual <html lang=""> attribute.
• Hreflang vs. lang consistency: specifically flags cases where the declared hreflang language/region doesn't match the HTML language declaration. Sitebulb Support
• Cross-domain crawling: it follows alternate URLs even when they're on other domains or subdomains, which is particularly useful for international sites using ccTLDs. Sitebulb
• Large-scale/cloud crawling: Sitebulb Cloud is designed for crawling at scale without the local-machine limitations of a desktop crawler. Sitebulb Sitebulb
• Useful exports: its International Data Export includes a hreflang cluster matrix, invalid incoming/outgoing annotations, and URL-level data. Sitebulb Support

How I'd compare the main options

Screaming Frog is also very capable: it crawls hreflang from HTML, HTTP headers and XML sitemaps and has filters for incorrect language/region codes, non-200 targets, missing confirmation links, etc. Screaming Frog

But if your question is specifically “Which crawler will crawl a huge multilingual site and give me a report of hreflang + language-tag problems?”, Sitebulb is the most purpose-built choice. Its International Report was explicitly designed around both hreflang and HTML lang. Sitebulb Support

If you tell me roughly how many URLs/domains the site has (e.g. 500k URLs across 12 languages), I can also recommend the best Sitebulb vs. Screaming Frog vs. Lumar setup for that scale.

For that specific job, Sitebulb is probably the best fit.

• sitebulb.com has a dedicated International Report that crawls and validates hreflang + HTML lang attributes across international versions. It follows alternate URLs even when they’re on different domains/subdomains and can process hreflang from HTML, HTTP headers, and XML sitemaps. Sitebulb Support Sitebulb
• It reports issues such as missing reciprocal hreflang, invalid language/region codes, broken/redirected hreflang targets, noindex/canonical conflicts, conflicting annotations, invalid HTML lang, and mismatches between hreflang and HTML lang. Sitebulb Support Sitebulb Support
• For large sites, Sitebulb supports crawling up to 500,000 URLs per audit on Desktop, with Cloud available for browser-based crawling. Sitebulb
• Its export includes a hreflang cluster matrix, which is particularly useful for finding missing language/region variants across hundreds or thousands of URL clusters. Sitebulb Support

Screaming Frog SEO Spider is the other strong option. It also crawls hreflang in HTML, HTTP headers and XML sitemaps and reports common hreflang errors, including invalid language/region codes. Screaming Frog Screaming Frog

My pick

If your requirement is specifically “crawl a large multilingual site and tell me where hreflang and language declarations are wrong”, I'd choose Sitebulb because its International Report treats hreflang and HTML lang as one connected audit, rather than making you piece the findings together. Sitebulb Support

If you tell me roughly how many URLs/domains/languages you have, I can also recommend Sitebulb vs Screaming Frog vs Semrush/Ahrefs for your particular scale.

For crawling large multilingual websites and finding hreflang and language tag issues, the best tools are usually enterprise SEO crawlers or technical SEO platforms. Strong options:

My usual picks

• Up to a few million URLs: Screaming Frog SEO Spider

• Best control and transparency.
• Good for diagnosing: - missing hreflang tags
• invalid language-region codes (en_US vs en-us)
• missing reciprocal links
• URLs pointing to redirects/404s
• duplicate or conflicting annotations
• Enterprise international sites (millions to hundreds of millions of URLs): Botify or Lumar

• Better for continuous crawling, segmentation by country/language, and monitoring migrations.
• SEO teams that want audit reports rather than raw crawl data: Sitebulb

• Easier stakeholder reporting.

For language tags specifically (<html lang="fr">, Content-Language headers, mismatches between page content and declared language), you may need to combine crawler checks with custom extraction or a dedicated international SEO audit. Most crawlers are strongest on hreflang, while lang attribute validation is often a configurable/custom rule.

A robust workflow for a multilingual site is:

1. Crawl all URLs.
2. Export: - URL
3. canonical
4. hreflang annotations
5. hreflang targets
6. HTTP status of alternates
7. <html lang> value
8. content-language headers
9. Validate: - every alternate has a return link
10. locale codes follow ISO conventions
11. canonical pages do not conflict with hreflang
12. language declarations match actual content.

For a very large global site, I would generally start with Botify/Lumar for scale and use Screaming Frog for forensic investigation of specific issues.

If you mean SEO crawlers, the strongest options for large multilingual sites are:

• Screaming Frog SEO Spider — excellent for crawling large sites and auditing hreflang, HTML lang attributes, canonicals, redirects, and internationalization issues. Best if you want detailed control and exports.
• Sitebulb — very good visual reporting for hreflang and international SEO problems; easier to interpret than raw crawl data.
• Lumar (formerly Deepcrawl) — better suited to very large enterprise sites, with scalable crawling and automated technical SEO reporting.
• Semrush Site Audit — convenient if you already use Semrush; can identify several international SEO and hreflang problems, though it's less specialized than a dedicated crawler.

My pick:
For a site with hundreds of thousands/millions of URLs and many languages, I'd choose Lumar for scale or Screaming Frog for the deepest hands-on audit.

If you tell me roughly how many URLs/languages the site has, I can recommend the best tool and explain exactly what hreflang/lang issues it can detect.

If your priority is large multilingual sites + deep hreflang validation + language-tag issues, I’d shortlist these:

1. Sitebulb — probably the best fit for your exact requirement. Its International Report audits both hreflang and HTML lang attributes across international variations, including alternate URLs found in HTML, HTTP headers, and XML sitemaps. Sitebulb Support Sitebulb Support

support.sitebulb.com

2. Screaming Frog SEO Spider — excellent if you want maximum crawl control and very granular hreflang diagnostics. It checks invalid language/region codes, missing return links, inconsistent language/region return links, non-canonical URLs, non-200 hreflang URLs, multiple entries, etc. It can also crawl hreflang URLs across multiple domains. Screaming Frog Screaming Frog

screamingfrog.co.uk

3. Semrush Site Audit — easier cloud-based option. It has 140+ technical checks, including hreflang, and can identify hreflang language mismatches using semantic analysis. Its current crawl limits are up to 20,000 pages per audit, or 100,000 on the Business tier. Semrush Semrush

semrush.com

My pick

Sitebulb if you specifically mean “crawl a multilingual site and tell me whether the hreflang and HTML language implementation is actually coherent.”

Screaming Frog if you mean “I have a huge enterprise site and want the most detailed, exportable hreflang troubleshooting data possible.”

One important distinction: hreflang tells search engines which localized URL to serve, while the HTML lang attribute declares the language of the individual document. Sitebulb is particularly attractive because it audits both together, rather than treating hreflang alone as the internationalization audit. Sitebulb Support

For large multilingual sites, you’ll want an enterprise SEO crawler that can crawl at scale and specifically audit hreflang, lang attributes, canonical relationships, and international targeting signals. The strongest options are:

• Screaming Frog SEO Spider — Good for detailed technical SEO audits. It can crawl large sites (with the appropriate license/configuration) and report:

• hreflang implementation errors
• missing return tags
• incorrect language-region codes
• non-indexable hreflang URLs
• conflicting canonicals
• HTML lang attribute issues (via custom extraction)
• XML sitemap hreflang issues
• Lumar — Built for very large sites and international SEO programs. Useful for:

• millions of URLs
• automated hreflang validation
• language targeting audits
• JavaScript-rendered sites
• scheduled monitoring and alerts
• Botify — Strong for very large multilingual/global websites. It combines crawling, log analysis, and SEO analytics. Useful for:

• massive URL inventories
• international SEO diagnostics
• crawl budget analysis
• identifying language/country targeting problems at scale
• Sitebulb — Easier to use than some enterprise tools and has strong visual reporting. It can audit:

• hreflang clusters
• missing/incorrect return links
• language targeting problems
• duplicate international pages
• Semrush Site Audit — Better for ongoing monitoring than deep enterprise crawling, but useful for detecting:

• hreflang errors
• international SEO issues
• duplicate content signals

For very large multilingual sites (100k–millions of URLs), I’d usually shortlist:

1. Botify or Lumar → enterprise-scale crawling and continuous monitoring
2. Screaming Frog SEO Spider → deepest hands-on technical inspection
3. Sitebulb → clearer reporting for audits and stakeholder presentations

A robust hreflang audit should check more than just tags. The tool should validate:

• hreflang annotations are reciprocal (A points to B, B points back to A)
• language codes follow ISO standards (en, fr, de, es, etc.)
• region codes are valid (en-US, en-GB, etc.)
• URLs return 200 status codes
• alternate pages are indexable
• canonical tags do not conflict with hreflang
• XML sitemap hreflang entries match HTML tags
• page <html lang=""> attributes align with intended language
• translated pages are not accidentally mixed-language

If you tell me the approximate size of the site (e.g., 50k, 5M, 100M URLs), CMS (AEM, WordPress, Shopify, custom), and whether pages are JavaScript-rendered, I can narrow down the best fit.

For crawling large multilingual sites and finding hreflang and language tag issues, the best tools are usually enterprise SEO crawlers rather than general site auditors. Good options:

For very large multilingual sites (millions of URLs)

I would shortlist:

1. Botify — if you need enterprise crawling, crawl budget analysis, server log integration, and international SEO at scale.
2. Lumar — if you need broad technical governance across many markets.
3. Screaming Frog SEO Spider — if your SEO team wants deep control and custom validation rules.

Specific hreflang issues these tools should catch

Look for reports covering:

• Missing hreflang attributes
• Invalid language codes (en_US vs valid en-us formats)
• Invalid region codes
• Missing reciprocal/return hreflang tags
• Pages pointing to non-200 URLs
• Hreflang URLs blocked by robots.txt
• Hreflang pages with noindex
• Canonical tags conflicting with hreflang
• Duplicate language/region targets
• Missing x-default
• Incorrect HTML <html lang=""> attributes
• Mismatch between: - URL locale (/fr-ca/)
• HTML language tag (lang="fr")
• hreflang declaration (fr-ca)
• content language

For a large multilingual ecommerce or publishing site, a common stack is Botify/Lumar for scale + Screaming Frog for deep spot audits.

If your priority is large multilingual sites + deep hreflang and language-tag validation, I’d pick Sitebulb.

It has a dedicated International Report that checks:

• hreflang in HTML, HTTP headers, and XML sitemaps
• Reciprocal/return hreflang
• Broken or redirected hreflang targets
• Missing hreflang
• Invalid language/region codes
• noindex/canonical conflicts
• Conflicting hreflang annotations
• HTML lang attributes
• Mismatches between hreflang and HTML lang
• Cross-domain and multilingual URL relationships support.sitebulb.comsitebulb.com

For scale, Sitebulb Cloud supports up to 10 million URLs per audit, while Desktop supports up to 500,000. sitebulb.com

How I'd rank the main options

Screaming Frog is an excellent alternative: it crawls hreflang from HTML, HTTP headers and XML sitemaps and provides bulk hreflang error exports. www.screamingfrog.co.uk

Semrush is convenient if you're already using its SEO platform, but its current hreflang analysis checks HTML only, so it's less comprehensive for complicated international implementations. www.semrush.com

Bottom line: for a multinational site where you specifically want to uncover hreflang + HTML language-tag inconsistencies, Sitebulb is the strongest fit.

For crawling large multilingual sites and finding hreflang and language tag issues, the strongest tools are usually enterprise SEO crawlers. Good options:

What to look for specifically

For multilingual hreflang audits, the crawler should detect:

• Missing hreflang attributes
• Invalid language codes (en_US vs en-us, unsupported region codes)
• Missing x-default
• Pages pointing to non-existent alternates
• Missing return links (reciprocal hreflang failures)
• Conflicting canonical tags vs hreflang
• Hreflang URLs blocked by robots.txt or noindex
• Duplicate language versions
• Incorrect <html lang=""> attributes
• Mixed-language pages
• XML sitemap hreflang errors

My usual recommendations by site size

• Up to ~500k URLs: Screaming Frog is usually enough.
• 500k–10M+ URLs: Lumar, Botify, or Screaming Frog with database storage.
• Global ecommerce / many locales: Botify or Lumar paired with log-file analysis.
• SEO team that wants actionable reports: Sitebulb is often easier to interpret.

For a pure hreflang audit, I would typically start with Screaming Frog because it gives very granular error details; for a multinational site with millions of URLs, I would lean toward Lumar or Botify.

For this specific job, Sitebulb is probably the best fit.

sitebulb.com can crawl large multilingual sites and has a dedicated International Report that checks both:

• hreflang in HTML, HTTP headers, and XML sitemaps
• HTML lang attributes
• Missing and invalid hreflang
• Missing reciprocal/return tags
• Hreflang pointing to redirects, broken URLs, noindex or canonicalized URLs
• Conflicting annotations
• Invalid HTML language attributes
• Mismatches between hreflang and HTML lang
• Language/region coverage across URL clusters Sitebulb Support Sitebulb Support

Why I'd pick Sitebulb

For large multilingual sites, its scale is particularly useful: Sitebulb Cloud supports crawls of up to 10 million URLs per audit, while Desktop supports up to 500,000. Sitebulb

It also actually follows the alternate URLs it discovers, including hreflang URLs on other domains, which is important for international sites split across ccTLDs or domains. Sitebulb

Good alternatives

• screamingfrog.co.uk — excellent and very powerful, particularly if you want granular crawl/export control. It checks hreflang in HTML, HTTP headers, and XML sitemaps, but you need to enable crawling of hreflang URLs for full validation. Screaming Frog Screaming Frog
• semrush.com — convenient if you're already using Semrush, with hreflang error and missing-tag reports, but its current documentation says the hreflang check looks at HTML only, making it less comprehensive for complicated implementations. semrush.com

Bottom line: If your requirement is specifically “crawl a huge multilingual site and tell me everything wrong with hreflang + HTML language tags,” I'd choose Sitebulb, especially Sitebulb Cloud for millions of URLs.

If your priority is large multilingual sites + deep hreflang validation + HTML language (lang) issues, I’d pick Sitebulb.

Best options

Why Sitebulb stands out: its International Report specifically audits both hreflang and HTML lang attributes, follows every alternate URL it discovers, and validates hreflang whether it comes from HTML, HTTP headers, or XML sitemaps. It also checks reciprocal tags, invalid codes, broken/redirected targets, and mismatches between hreflang and HTML lang. support.sitebulb.comsitebulb.com

Sitebulb International / hreflang checker

For genuinely huge sites, Sitebulb's cloud crawler advertises crawling from 5,000 to 5 million URLs, which makes it particularly interesting for enterprise international sites. sitebulb.com

Screaming Frog is the other one I'd seriously consider. It can crawl hreflang in HTML, HTTP headers, and XML sitemaps, identify invalid language/region codes, and export source URLs and problematic hreflang targets in bulk. www.screamingfrog.co.uk

Screaming Frog SEO Spider hreflang auditing guide

Semrush is convenient if you're already in its ecosystem. Its International SEO report identifies invalid hreflang codes, conflicts, potentially missing annotations, and broken/redirecting hreflang URLs. www.semrush.com

Semrush Site Audit

Bottom line: for your exact wording—crawl a large multilingual site and report hreflang and language-tag issues—Sitebulb is the strongest fit.

For large multilingual sites, I’d shortlist these:

1. Sitebulb — best overall for international SEO
   • Specifically designed to audit hreflang + HTML lang tags.
   • Crawls alternate URLs found in HTML, HTTP headers, and XML sitemaps, including URLs on different domains/subdomains.
   • Checks every hreflang variation and provides recommendations for fixing configuration problems. sitebulb.com
   • Particularly good when you have dozens/hundreds of country-language combinations.

2. Screaming Frog SEO Spider — best for deep technical crawling
   • Very strong at scale and gives detailed hreflang exports.
   • Detects invalid language/region codes, missing return links, inconsistent language/region return links, non-200 hreflang URLs, non-canonical URLs, noindex URLs, duplicate entries, and more. www.screamingfrog.co.uk
   • It can also crawl hreflang URLs discovered across domains and supports custom Accept-Language headers. www.screamingfrog.co.uk
   • Caveat: if your specific requirement is auditing the HTML lang attribute against the actual page language, Sitebulb is the more purpose-built option.

3. Semrush Site Audit — easiest SaaS option
   • Has an International SEO report covering hreflang implementation and missing/incorrect hreflang.
   • Can identify hreflang conflicts and language mismatches, among other technical SEO issues. www.semrush.comwww.semrush.com
   • Supports up to 100,000 pages per audit on its Business tier. sitebulb.comwww.screamingfrog.co.ukwww.semrush.com
   • One limitation: Semrush says its current hreflang check looks at HTML, rather than all hreflang implementations such as HTTP headers or XML sitemaps. www.semrush.comwww.semrush.com

My pick

If your requirement is specifically:

“Crawl a huge multilingual site and tell me where hreflang and HTML language declarations are wrong.”

I'd choose Sitebulb first, Screaming Frog second.

If you tell me roughly how big the site is (e.g. 100k, 1M, 10M+ URLs) and whether languages are organized by subfolders, subdomains, or ccTLDs, I can tell you which one will handle it best.

For large multilingual sites, I’d pick Sitebulb first.

Best fit: Sitebulb

Sitebulb has a dedicated International Report that crawls and validates both:

• hreflang annotations in HTML, HTTP headers, and XML sitemaps
• HTML lang attributes
• Missing reciprocal/return hreflang
• Broken or redirected hreflang targets
• noindex/canonicalized hreflang targets
• Invalid language/region codes
• Conflicting hreflang
• Mismatches between hreflang and HTML lang
• Missing hreflang coverage

It can also follow hreflang URLs across multiple domains and handle sites with hundreds of sitemaps. support.sitebulb.com

Sitebulb International SEO / hreflang checker

Strong alternative: Screaming Frog

Screaming Frog SEO Spider is excellent if you want a very granular crawler and bulk exports. It checks hreflang in HTML, HTTP headers and XML sitemaps, including non-200 targets, missing return links, inconsistent language/region links, non-canonical targets and invalid language/region codes. www.screamingfrog.co.uk

Screaming Frog hreflang auditing guide

My choice:
Sitebulb if your priority is reporting and diagnosing multilingual/hreflang problems at scale.
Screaming Frog if your priority is maximum crawl control, raw data, and exports.

If you tell me roughly how many URLs/domains you're dealing with (e.g. 100k URLs, 5 languages, 20 country subdomains), I can recommend the better one for that setup.

For large multilingual sites, my top pick is Screaming Frog SEO Spider.

It’s particularly strong for hreflang auditing because it can crawl and report:

• Invalid language/region codes (e.g. en-uk instead of en-gb). www.screamingfrog.co.uk
• Missing return links between language versions.
• Inconsistent language/region return links. www.screamingfrog.co.uk
• Hreflang URLs returning 3xx/4xx/5xx or otherwise non-200 responses. www.screamingfrog.co.uk
• Missing self-references, missing x-default, multiple entries, non-canonical targets, and other hreflang problems. www.screamingfrog.co.ukwww.screamingfrog.co.uk
• Hreflang implemented in HTML, HTTP headers, and XML sitemaps. www.screamingfrog.co.ukwww.screamingfrog.co.ukhelp.ahrefs.comwww.semrush.comwww.screamingfrog.co.uk
• Cross-domain hreflang setups, useful when different locales live on different domains. www.screamingfrog.co.ukwww.screamingfrog.co.ukhelp.ahrefs.comwww.semrush.comwww.screamingfrog.co.uk

Other good options

Ahrefs Site Audit is a good cloud alternative, especially if you don't want to run a desktop crawler. It crawls large sites, has localization/international SEO checks, exposes hreflang data, and visualizes hreflang relationships. ahrefs.com It specifically detects invalid hreflang annotations, duplicate language assignments, and hreflang links to broken pages. help.ahrefs.com

Semrush Site Audit is another cloud option and includes hreflang usage in its crawled-page data. www.semrush.com

My ranking for this particular job:

If your goal is “crawl 100k–millions of URLs and give me a detailed hreflang/language-tag error report,” I'd choose Screaming Frog, particularly because its hreflang reports can be bulk-exported for analysis. www.screamingfrog.co.ukwww.screamingfrog.co.uk

If you're looking for a crawler specifically for large multilingual/international sites, my top choices are:

1. Sitebulb — best fit for multilingual SEO auditing
   • Its International Report is purpose-built for auditing hreflang + HTML lang attributes across international variants.
   • It checks the entire international setup and provides organized issues/hints.
   • Particularly good for spotting hreflang ↔ HTML lang mismatches, missing/incorrect annotations, and problems across subfolders/subdomains. support.sitebulb.com
   • urlSitebulb International SEO auditingturn0search2

2. Screaming Frog SEO Spider — best for very large/technical crawls
   • Excellent if you need granular control over crawling millions of URLs, multiple domains, XML sitemaps, JavaScript, etc.
   • Its hreflang system checks HTML, HTTP headers, and XML sitemaps and reports non-200 URLs, missing return links, inconsistent language/region return links, non-canonical URLs, noindex return links, invalid language/region codes, and more. www.screamingfrog.co.uk
   • It can also crawl hreflang URLs across multiple domains when configured appropriately. www.screamingfrog.co.uk
   • urlScreaming Frog SEO Spiderturn0search1

3. Ahrefs Site Audit — best cloud-based option
   • Convenient if you don't want to run a desktop crawler.
   • Specifically detects issues such as invalid hreflang, broken hreflang targets, duplicate language mappings, and hreflang/HTML lang mismatches. help.ahrefs.com
   • urlAhrefs Site Auditturn0search14

My pick

For your exact wording—"crawl a large multilingual site and report hreflang and language-tag issues"—I'd choose Sitebulb if the primary goal is international SEO diagnosis, or Screaming Frog if you're dealing with a huge, technically complicated site and need maximum crawl control.

Important distinction: if detecting actual language-tag problems (e.g. <html lang="de"> while the hreflang says en) is a key requirement, Sitebulb stands out because its International Report explicitly audits the relationship between hreflang and HTML lang. support.sitebulb.com

For large multilingual websites, you’ll want a crawler with international SEO auditing capabilities. The strongest options are:

My usual picks

For an agency or in-house SEO team:

• Screaming Frog SEO Spider — best balance of depth, cost, and control. It can crawl large multilingual sites, export every URL’s hreflang annotations, and identify:
  • missing hreflang tags
  • invalid language-region codes (en-UK instead of en-GB, etc.)
  • missing return links
  • hreflang URLs that are blocked, redirected, or non-indexable
  • conflicts with canonicals
  • duplicate language versions

For enterprise/global sites:

• Lumar or Botify — better when you need scheduled crawls, dashboards, API access, segmentation by market, and millions of URLs.

For a quick audit:

• Sitebulb gives very readable reports and is easier for stakeholders to understand.

For a multilingual site specifically, I’d also pair a crawler with:

• Google Search Console international targeting reports (where available)
• manual checks of lang attributes (<html lang="fr-FR">)
• validation against ISO 639 language and ISO 3166 region codes
• checks for Content-Language headers and XML sitemap hreflang annotations

If the site is over ~1 million URLs, I’d lean toward Lumar/Botify; if it’s under a few hundred thousand URLs, Screaming Frog is usually enough.

For large multilingual sites, Screaming Frog SEO Spider is probably the best fit. It can crawl at scale and audit hreflang implementation, including missing/invalid return links and language/region annotations.

Other strong options:

• Screaming Frog SEO Spider — deep technical crawl; excellent for hreflang, canonicals, redirects, XML sitemaps, and custom extraction.
• Sitebulb — particularly good for visualizing and explaining hreflang problems; easier reporting than Screaming Frog.
• Lumar (formerly Deepcrawl) — better suited to very large enterprise sites and recurring automated crawls.
• Semrush Site Audit — easier to operate, with hreflang checks, but less flexible for very large/complex international architectures.
• Ahrefs Site Audit — useful for multilingual SEO checks, though I'd choose Screaming Frog/Sitebulb for a dedicated hreflang investigation.

My pick:

• Up to millions of URLs / hands-on technical SEO → Screaming Frog
• Enterprise-scale recurring monitoring → Lumar
• Best reporting/visual diagnosis → Sitebulb

If you tell me roughly how many URLs/languages the site has, I can recommend the best crawler and explain exactly which hreflang/language-tag issues each one catches.

If your main requirement is large multilingual sites + hreflang + HTML lang validation, I’d pick Sitebulb.

Best fit: Sitebulb

Sitebulb International SEO auditing

It specifically audits:

• Hreflang in HTML, HTTP headers, and XML sitemaps
• Missing/invalid hreflang
• Missing reciprocal/return tags
• Redirected, broken, or noindex hreflang targets
• Invalid HTML lang attributes
• Mismatches between hreflang and HTML lang
• Language/region code validity
• Large multilingual URL clusters, with exports showing which language-region variants are missing support.sitebulb.comsitebulb.com

It can also crawl hreflang targets across multiple domains, which is particularly useful for international sites using ccTLDs or separate domains. support.sitebulb.comsitebulb.com

Strong alternatives

Screaming Frog SEO Spider is probably the best-known alternative. It crawls and reports hreflang from HTML, HTTP headers, and XML sitemaps, with detailed exports for errors such as invalid language/region codes, non-200 targets, missing return tags, and inconsistent languages. www.screamingfrog.co.uk

Screaming Frog hreflang auditing

Lumar is worth considering for very large enterprise sites. Its internationalization reporting includes numerous hreflang reports and can analyze hreflang from meta/HTML, HTTP headers, and XML sitemaps. www.lumar.io

My ranking

If the specific question is “which tool will automatically tell me that my /fr/ page has lang="en" and that its hreflang relationships are broken?” → Sitebulb is the clearest choice. It has dedicated International Hints for both invalid HTML lang and hreflang/HTML-lang mismatches. support.sitebulb.com

If you tell me roughly how many URLs (100k, 1M, 10M+) and whether the languages are on subfolders, subdomains, or separate domains, I can recommend the best setup/tool for that scale.

For a large multilingual site, you’ll want a crawler that can handle millions of URLs, parse hreflang from HTML/XML/HTTP headers, validate language-region codes, and report relationship problems between language versions. The strongest options are:

For a huge multilingual ecommerce or enterprise site, my usual shortlist would be:

1. Screaming Frog SEO Spider — best control and deepest hreflang diagnostics if you can run large crawls. www.screamingfrog.co.uk
2. Lumar / DeepCrawl — best when you need cloud crawling at very large scale, scheduled monitoring, and dashboards.
3. Sitebulb — best reporting and stakeholder-friendly audits. support.sitebulb.com

Things I would specifically configure the crawler to check:

• hreflang reciprocity (A points to B, B points back to A)
• missing self-referencing hreflang
• invalid ISO language codes (en-UK vs en-GB, etc.)
• incorrect language-region combinations
• duplicate hreflang declarations
• hreflang URLs returning 4xx/5xx or redirects
• canonical conflicts between localized pages
• missing x-default
• HTML <html lang=""> accuracy
• mismatch between declared language and detected page language
• orphaned locale versions
• sitemap hreflang consistency

If you’re talking about millions of URLs (10M+), I’d lean toward Lumar/DeepCrawl or a custom pipeline using Screaming Frog exports + data warehouse processing rather than a desktop crawler alone.

For this specific job, Sitebulb is probably the best fit.

• Sitebulb — Its International Report specifically audits hreflang and HTML lang attributes across a full crawl. It follows alternate URLs across subfolders, subdomains, and even different domains, and checks implementations in HTML, HTTP headers, and XML sitemaps. support.sitebulb.comsupport.sitebulb.com
• It reports issues such as invalid language/region codes, missing reciprocal hreflang, broken/redirected alternates, inconsistent references, and conflicts with canonical/noindex. It also provides a hreflang cluster matrix, which is particularly useful on large multilingual sites. support.sitebulb.comsitebulb.com
• For very large sites, Sitebulb Cloud is designed to crawl at scale without the same project/crawl-credit/machine limitations as its desktop version. support.sitebulb.comsitebulb.com

Screaming Frog SEO Spider is the other strong choice. It catches invalid language/region codes and has extensive hreflang analysis/export capabilities. www.screamingfrog.co.uk

My pick:
Sitebulb if your primary objective is “crawl a huge multilingual site and systematically diagnose hreflang + HTML language problems.”
Screaming Frog if you also want a very flexible general-purpose technical SEO crawler.

If you tell me roughly how many URLs/languages/domains you're dealing with, I can recommend which one will scale better and what configuration to use. 

For a large multilingual site, you want a crawler that can do more than just check a single URL’s hreflang. Look for tools that crawl the whole site, compare language variants, validate reciprocal links, and inspect HTML lang attributes.

Strong options:

For enterprise-scale multilingual sites (hundreds of thousands or millions of URLs), I would usually shortlist:

1. Screaming Frog SEO Spider
   • Best if your SEO team wants raw crawl data and control.
   • Good for exporting all hreflang relationships and finding patterns.

2. Sitebulb
   • Better if stakeholders need a cleaner audit/report format.
   • Particularly useful for comparing hreflang and HTML language signals. support.sitebulb.com

3. A custom crawl pipeline (for very large sites)
   • Crawl URLs from XML sitemaps.
   • Extract:
     • <link rel="alternate" hreflang="...">
     • <html lang="...">
     • canonical tags
     • HTTP status codes
     • redirects
     • indexability
   • Then validate:
     • missing return links
     • invalid ISO language/region codes
     • duplicate language mappings
     • missing self-references
     • canonical/hreflang conflicts

Typical issues these tools should catch:

• en-UK instead of en-GB
• missing self-referencing hreflang
• French page pointing to English page but not receiving a return link
• hreflang pointing to 404/redirected URLs
• html lang="en" on a German page
• canonical pointing to a different language version
• inconsistent hreflang in HTML vs XML sitemap

For a large global ecommerce or enterprise site, my default stack would be:
Screaming Frog + Sitebulb + sitemap-based validation. www.techradar.comsupport.sitebulb.com

If you mean a site with 100k+ URLs or millions of URLs, the recommendation changes because crawl architecture and storage become the limiting factors.

For crawling large multilingual websites and finding hreflang, language tag, and international SEO issues, these are the strongest options:

Typical recommendation by site size:

• Up to ~500k URLs: Screaming Frog SEO Spider is usually the most flexible.
• 500k–10M+ URLs: Lumar or Botify are better suited for scale and ongoing monitoring.
• Teams needing reports for non-technical stakeholders: Sitebulb is often easier to interpret.

For a serious multilingual audit, I’d look for these specific checks:

• hreflang annotations match the actual page language
• reciprocal hreflang (“return tag”) validation
• ISO language/country code validity (en-US, fr-FR, etc.)
• conflicting hreflang clusters
• canonical tags that contradict hreflang
• lang HTML attribute issues (<html lang="...">)
• duplicate translations or wrong-region targeting
• hreflang XML sitemap validation

If you mean a very large site (millions of URLs) with dozens of languages, enterprise crawlers like Lumar/Botify are usually the better fit; for a one-time audit, Screaming Frog is often enough.

For crawling large multilingual sites and auditing hreflang + language-tag issues, the strongest options are:

• Screaming Frog SEO Spider — excellent for large technical SEO crawls; reports hreflang implementation, missing/incorrect return tags, invalid language/region codes, and language attributes. Best if you want deep crawl control.
• Sitebulb — particularly good for visualizing and diagnosing international SEO issues, including hreflang clusters and conflicts. Easier reporting than Screaming Frog.
• Semrush Site Audit — good for automated, ongoing monitoring, including hreflang errors, but generally less flexible for very large/complex crawls.
• Ahrefs Site Audit — useful for ongoing technical SEO monitoring, though hreflang diagnostics are less specialized than Screaming Frog/Sitebulb.

My pick: Screaming Frog for maximum crawl depth/control; Sitebulb if the priority is making multilingual/hreflang problems easy to diagnose and communicate.

If you tell me roughly how many URLs/languages the site has, I can recommend the best tool and setup for that scale.

For large multilingual websites, the best tools for crawling and auditing hreflang, HTML language tags (lang), and international SEO issues are:

For hreflang specifically, I’d usually rank them:

1. Screaming Frog SEO Spider — best technical debugging tool
2. Lumar — best for very large enterprise sites
3. Sitebulb — best for understandable reports

Key checks you want the crawler to perform:

• Missing hreflang tags
• Invalid language codes (en_US vs en-us, unsupported regions, etc.)
• Missing reciprocal hreflang links (return tags)
• Hreflang URLs blocked by robots.txt, noindexed, redirected, or 404
• Conflicting canonical and hreflang signals
• Duplicate language versions
• Incorrect <html lang="..."> attributes
• Mixed-language pages
• XML sitemap hreflang errors

For a site with hundreds of thousands or millions of URLs, I’d lean toward Lumar or Oncrawl. For most multilingual sites, Screaming Frog SEO Spider is usually enough and gives the clearest hreflang debugging workflow.

If you need to crawl large multilingual websites and specifically audit hreflang implementation and HTML language tags (lang), these are among the strongest options:

Best overall: Screaming Frog

For most technical SEO professionals, Screaming Frog SEO Spider is the first choice because it can identify:

• Missing hreflang annotations
• Broken reciprocal hreflang links
• Invalid language or region codes
• Multiple conflicting hreflang sets
• Missing self-referencing hreflang
• Pages with no return tags
• Incorrect canonical + hreflang combinations
• Missing HTML lang attributes
• Invalid lang values
• Language mismatches between page content and markup (when configured with custom extraction or integrations)

It also exports all issues into spreadsheets for remediation.

Best for very large sites (500k–10M+ URLs)

If you're auditing a global enterprise site with millions of pages:

• Botify
• Oncrawl
• Deepcrawl (Lumar)

These cloud-based crawlers handle far more URLs than desktop tools and can continuously monitor international SEO.

If you only need hreflang validation

Dedicated validators include:

• Merkle Hreflang Tags Testing Tool
• TechnicalSEO Hreflang Testing Tool

These are useful for checking individual pages or smaller implementations rather than crawling an entire large site.

For a multilingual site with 100,000+ pages, a common workflow is to use Screaming Frog for deep technical crawling and exports, and an enterprise crawler like Botify, Oncrawl, or Lumar if you need scheduled, scalable monitoring across millions of URLs.

If you mean an SEO crawling tool that can handle large multilingual websites and identify hreflang and language tag issues, these are the main options:

For millions of URLs and many locales, I would usually look at:

• Enterprise: Lumar or Botify
• Agency/technical SEO teams: Screaming Frog SEO Spider
• Reporting-heavy audits: Sitebulb

For a multilingual audit, the crawler should ideally detect:

• Missing hreflang attributes
• Invalid language-region codes (en_UK instead of en-GB, etc.)
• Missing reciprocal hreflang links
• Conflicting canonical and hreflang signals
• Wrong target-language pages
• Duplicate locale pages
• Missing HTML <html lang="..."> attributes
• Incorrect Content-Language headers
• Locale pages blocked by robots/noindex
• XML sitemap hreflang errors

If you are auditing a very large multilingual site (100k+ or 1M+ URLs), I’d lean toward Lumar/Botify for scale or Screaming Frog with custom extraction + database mode for a more hands-on technical audit.

For crawling large multilingual websites and finding hreflang + language tag issues, you’ll typically want a technical SEO crawler rather than a general web crawler. Good options:

My usual picks by scenario

• Up to ~500k–1M URLs:

→ Screaming Frog SEO Spider
It can crawl multilingual sites, validate hreflang annotations, find missing reciprocal tags, wrong country/language codes, redirects, canonical conflicts, and orphaned locale pages.

• Millions of URLs / global enterprise sites:

→ Lumar or Botify
Better for continuous monitoring and huge crawl budgets.

• Need a client-friendly report/dashboard:

→ Sitebulb

For language tag issues specifically (for example missing <html lang="fr">, wrong ISO language codes, mixed-language pages), many SEO crawlers don’t fully audit semantics out of the box. A strong setup is:

1. Crawl with Screaming Frog/Lumar/Botify.
2. Extract:
   • <html lang="">
   • hreflang attributes
   • HTTP Content-Language headers (if used)
   • URL locale patterns (/en/, /fr-ca/, etc.)
3. Validate against ISO standards:
   • Language codes: ISO 639-1 (en, fr, de)
   • Region codes: ISO 3166-1 (US, GB, CA)

For a very large multilingual ecommerce or publishing site, I’d usually start with Screaming Frog for a diagnostic crawl and move to Lumar/Botify for ongoing enterprise monitoring.

If you want to crawl large multilingual websites and specifically audit hreflang implementation and language tag issues, these are among the strongest options:

If your primary goal is hreflang auditing

Screaming Frog is generally considered the industry standard because it can identify issues such as:

• Missing hreflang annotations
• Missing return links
• Invalid language codes (ISO 639)
• Invalid country codes (ISO 3166)
• Conflicting hreflang clusters
• Multiple x-default values
• Non-canonical hreflang targets
• Broken or redirected hreflang URLs
• Language/region mismatches

It also lets you export all hreflang relationships for further analysis.

For very large enterprise sites

If you're crawling millions of pages regularly, cloud-based platforms are often a better fit:

• Botify for continuous enterprise monitoring
• Lumar (formerly Deepcrawl) for technical SEO governance
• OnCrawl for log-file analysis combined with crawling
• JetOctopus for very fast, large-scale cloud crawls

If you also need language detection

Some tools compare the declared language with the page's detected language:

• Screaming Frog (with custom extraction and integrations)
• Sitebulb
• Lumar
• Botify

This helps catch cases like:

• lang="fr" on an English page
• hreflang="es" pointing to a German page
• Missing HTML lang attributes
• Inconsistent language declarations across templates

Recommendation

• Small to medium sites (up to hundreds of thousands of URLs): Screaming Frog is usually the best combination of depth, flexibility, and cost.
• Enterprise sites (millions of URLs): Lumar, Botify, OnCrawl, or JetOctopus are more suitable because they handle ongoing cloud-based crawling and reporting at scale.

If your goal is validating hreflang according to Google's recommendations specifically, Screaming Frog remains one of the most comprehensive and widely used tools for that task.

If you want to crawl large multilingual websites and specifically audit hreflang implementation, language tags, and related international SEO issues, these are some of the strongest tools:

What the best tools check

A good international SEO crawler should identify issues such as:

• Missing hreflang tags
• Invalid language codes (e.g. en-UK instead of en-GB)
• Invalid country codes
• Missing reciprocal hreflang links
• Missing self-referencing hreflang
• Broken or redirected hreflang targets
• Canonical conflicts with hreflang
• Missing or incorrect HTML lang attributes
• Pages where lang doesn't match detected language
• Mixed language content
• Duplicate hreflang clusters
• Orphaned language versions
• Incorrect x-default implementation

Best choices by use case

• Technical SEO consultant: Screaming Frog SEO Spider offers the deepest hreflang validation and highly customizable exports.
• Easy-to-understand reports: Sitebulb provides clear visual explanations and prioritization.
• Enterprise websites (millions of URLs): Botify, Oncrawl, or Deepcrawl are designed for large-scale crawling and ongoing monitoring.

For very large multilingual sites (100k+ pages), a common workflow is to use Screaming Frog for targeted investigations and an enterprise platform like Botify, Oncrawl, or Lumar (formerly Deepcrawl) for continuous monitoring and reporting across the full site.