Google Says Skip llms.txt. Its Own Tool Checks for It Anyway. Here's What SEOs Should Know.

Google is sending two contradictory signals on llms.txt — and both are coming from inside the house.

On May 15, Google's Search Central published its official AI search optimisation guide. It named llms.txt directly in a mythbusting section, grouping it alongside content chunking and AI-specific schema as tactics that do not help with AI Overviews, AI Mode, or any generative AI Search feature.

Gary Illyes confirmed publicly: Google does not support llms.txt and has no plans to.

Five days later, Google shipped Lighthouse 13.3. The update added a new "Agentic Browsing" audit category — and one of its checks flags whether your site provides an llms.txt file. The Chrome team's documentation describes it as "a machine-readable summary of a website's content, specifically designed for LLMs and AI agents," warning that without it, agents may spend more time crawling your site to understand its structure. Same company. Opposite guidance.

The distinction that resolves it: these are two different surfaces. Google Search doesn't use llms.txt for rankings or citations — Googlebot renders real HTML and doesn't need a summary file.

Browser-based AI agents (the kind being standardised via WebMCP, confirmed for Chrome 149 origin trial) operate differently — they navigate pages like users, and a structured summary helps them act faster.

The practical takeaway for SEOs:

• Don't add llms.txt expecting a Google Search or AI Overview ranking boost — it won't deliver one

• Do consider it if AI agents (Anthropic, OpenAI, Perplexity) are a meaningful traffic source for your site

• Watch WebMCP closely — it's the bigger standard, and it's moving fast

The agentic web is being built in real time. This contradiction isn't confusion — it's the seam between two eras of search showing.