Google Adds llms.txt Check to Chrome Lighthouse

An "Agentic Browsing" audit item has been added to Google Chrome's Lighthouse, and it checks for the presence of an llms.txt file. This is presented as a signal for the efficiency with which AI agents navigate a site.

What it checks:

• WebMCP integration
• Accessibility tree integrity
• Layout stability via CLS
• Presence of an llms.txt file

Google explained that "without llms.txt, agents may spend more time understanding a site's structure." However, unlike traditional Lighthouse, it does not assign a 0-100 score, only showing a pass/fail ratio.

Point of controversy: In a guide published a week earlier, Google stated that "llms.txt is not required for Search optimization." John Mueller explained that "this is for functionality, not SEO (discovery)," describing it as a "temporary aid" that helps AI coding tools easily parse reference material, similar to developer documentation.

This also aligns with the Agentic Engine Optimization concept proposed by Google Cloud's Addy Osmani in April. This includes clean semantic structure, token-efficient content, Markdown delivery, and llms.txt.