Build‑Time SEO Checks in Gatsby

Gatsby gives you a useful moment to catch SEO problems: the build.

By the time the build runs, Gatsby knows which pages it is creating, which data those pages use, which templates render them, and which generated files will be deployed. That makes build time a good place to catch missing metadata, broken routes, invalid sitemap entries, and content model gaps before they become production issues.

Check Routes as Data

Every generated page should have a valid route.

Build‑time checks can catch:

• missing slugs
• duplicate slugs
• unexpected uppercase paths
• invalid characters
• trailing slash inconsistencies
• pages created for draft content
• pages missing from expected collections

This is especially useful when routes come from a CMS. A content editor may not realise a slug field has broken the build until the build explains it clearly.

Validate Metadata Before Rendering

SEO metadata often comes from several places:

• CMS fields
• template defaults
• site‑wide settings
• generated fallbacks
• page type rules

Build‑time checks can make sure each indexable page has a title, description, canonical URL, and any required social metadata.

The key is not to require every field manually. Good defaults are useful. The check should make sure the final output is specific enough and not accidentally duplicated everywhere.

Check Canonical and Sitemap Alignment

Sitemaps and canonicals should agree.

If a page appears in the sitemap, it should usually have a self‑referencing canonical unless there is a deliberate reason not to. If a page is noindex, it probably should not be in the sitemap.

The existing article on automatically generating text sitemaps in Gatsby covers one generated output. The same principle applies to XML sitemaps, route manifests, and other discovery files.

Validate Structured Data Carefully

If Gatsby generates JSON‑LD during build, that output can be checked.

Useful checks include:

• valid JSON
• expected schema type
• required fields present
• URLs are absolute
• dates are valid
• image references exist
• schema content matches visible page content

Do not use build‑time checks to force schema onto pages that do not support it. Use them to keep chosen schema honest.

Compare CMS References

CMS‑driven pages often depend on referenced entries.

An article may need an author. A project page may need related services. A product page may need category data. If those references are missing, unpublished, or malformed, the page can render weak or broken SEO output.

Build‑time checks should report the entry and field that caused the problem. "Cannot read property title of undefined" is not an editorially useful error.

Include Redirects and Legacy URLs

Gatsby sites often include redirect generation.

Check:

• old URLs have targets
• redirect chains are avoided
• redirects do not point to missing pages
• internal links use the final URL where possible
• important migrated pages are covered

SEO migrations fail when route generation and redirect generation are treated as separate worlds.

The same thinking belongs in migration work. How to compare rendered HTML before and after a migration and technical SEO launch criteria for a Next.js migration take the same evidence‑first approach beyond Gatsby.

Wrapping Up

Build‑time SEO checks are useful because they catch repeated template and data problems before deployment.

Use the Gatsby build to validate routes, metadata, canonicals, sitemaps, structured data, CMS references, and redirects. A stricter build is only useful when the errors point to real output risk.

Key Takeaways

• Gatsby builds are a good point to validate route and SEO data.
• Metadata checks should inspect final page output, including fallbacks.
• Canonicals, sitemaps, noindex, and generated routes should align.
• Structured data should be valid and supported by visible content.
• CMS reference errors should explain the affected entry and field clearly.