Lighthouse's llms.txt audit, explained

Google's Lighthouse added an llms.txt audit to its Agentic Browsing category. Google's scoring docs (fetched 2026-10-15 07:04 EDT, page last updated 2026-05-05) say: "The Agentic Browsing category and WebMCP support are experimental and based on proposed standards. Testing this category requires Chrome 150 or later". They describe the llms.txt check as: "Checks for the presence of a machine-readable summary at the domain root."

How the audit decides (Google's docs, page last updated 2026-05-05)

From developer.chrome.com/docs/lighthouse/agentic-browsing/llms-txt (fetched directly):

• "Lighthouse flags the pages if a server error occurs when attempting to retrieve the llms.txt file."
• "If the file is not provided by the server (resulting in a 404), the audit is marked as Not Applicable (N/A), as providing the file is optional at the moment."
• Fix: place the file "in the root directory of your website (for example, https://example.com/llms.txt)" and follow the llms.txt specification.

So:

Things people get wrong

• "Missing llms.txt fails Lighthouse." No. A 404 is N/A.
• The real failure mode is a server error. A misconfigured route, a CDN rule or a plugin that throws a 500 on /llms.txt gets flagged even though you never meant to publish one.
• Root only. Google's fix text says root. v2 of the proposal also allows subpath files like /docs/llms.txt (llmstxt.org), but Google's scoring docs describe the check as looking "at the domain root", so a subpath-only file likely isn't what the audit sees (our inference). Put one at the root if you want the audit to see it.
• No overall score. Google: "Unlike other Lighthouse categories, the Agentic Browsing category does not have a weighted average score from 0 to 100." Instead it shows "A fractional score: A ratio showing how many agentic readiness checks your site passes." (scoring docs) Our checker's 0–100 is our own format score and isn't related to Lighthouse.
• Passing isn't ranking. It's an audit in an experimental category. Nothing in Google's docs says it affects Search.

How to check before you run Lighthouse

1. curl -I https://yoursite.com/llms.txt and confirm the status is 200 (or a deliberate 404), not a 5xx.
2. Make sure the first content line is # Your site name.
3. Paste the file into our checker. It tests the H1 and the rest of the format. No file yet? Generate one, upload it to the root, and re-run the audit.

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