AI assistants now answer questions like "who is the best plumber near me" by reading websites. An llms.txt file is a small, plain-text page at the root of your site that tells them who you are and which pages to read first.
It is an emerging convention, not a standard, and no engine has promised to use it. It takes about ten minutes, so I add one to every site I build.
The format is Markdown with four parts, in this order:
> Emergency and planned plumbing for homes in Bristol, open seven days a week.
## Services
- [Boiler repair](https://example.com/boiler-repair): Same-day repairs for gas boilers, with fixed call-out prices.
- [Bathroom fitting](https://example.com/bathrooms): Full bathroom installs, from design to tiling.
## About
- [Pricing](https://example.com/pricing): Call-out fees and hourly rates.
- [Contact](https://example.com/contact): Phone, email and service area.
https://yourdomain.com/llms.txt, with a 200 status.
An llms.txt is no use if the crawlers are blocked. Look for rules that disallow GPTBot, ClaudeBot or PerplexityBot. Some security plugins and CDN settings add these for you, so it is worth reading the file your site actually serves.
A good llms.txt helps an engine read your site. It does not make the engine recommend you. The only way to know whether you are mentioned is to ask the engines the questions your customers ask, and read the answers.
I build MentionMachine, which has a free llms.txt generator. It builds the file from what you type and can validate one you have already published. There is no account, and nothing is rewritten by a model. There is also a robots.txt checker for AI crawlers.
If you have added an llms.txt to your own site, I would like to hear whether you saw any change.