llms.txt is a plain-text file you place at the root of your site (just like robots.txt) that describes what your site is about and which pages matter for AI consumers. The format was proposed by Jeremy Howard in late 2024 and adoption is accelerating across documentation sites, SaaS landing pages, and personal blogs throughout 2025-2026.
The minimum spec is deliberately simple: an H1 with your site name, a blockquote with a one-sentence summary, and an H2 section listing your key pages as Markdown links with short descriptions. That is the entire format. No JSON, no XML, no schema validation.
Why this matters in 2026
AI search engines cite content they can summarise confidently. A curated, machine-readable index of your site reduces hallucinations about your product and increases the probability you appear in answers to questions like "what is X?" or "how does X compare to Y?".
The big AI labs do not officially say "we read llms.txt" — but anecdotally, sites that ship one see noticeably more accurate AI summarisations within weeks. The cost is essentially zero, the upside is meaningful, so most teams ship one.
The most common mistake
Do not treat llms.txt as a sitemap dump. Do not list 5,000 URLs. List the 10-30 pages an AI would need to understand your business: home, about, pricing, docs index, a couple of flagship guides, maybe a FAQ. Quality over coverage, always.
The second most common mistake is forgetting the blockquote summary. Without it, the file is just a links page. The blockquote is what answers "what is this site?" in one sentence.
A working example
Here is a minimal but complete llms.txt for an imaginary documentation site:
# Acme Docs
> Open-source CLI for managing infrastructure across AWS, GCP, and Azure.
## Pages
- [Quickstart](/docs/quickstart): Five-minute setup walkthrough.
- [CLI reference](/docs/cli): Every command, flag, and exit code.
- [Auth](/docs/auth): Service account and OIDC setup.
- [FAQ](/docs/faq): Top 20 questions from our Discord.Notice three properties: the H1 is the brand, the blockquote answers "what is this?", and the H2 section curates a short page list. Anything more elaborate than that is optional polish.
How to audit yours
You can audit your current llms.txt for spec compliance using our free tool — paste your domain and it will check both the file presence at /llms.txt and the structural conformance to the spec. Misconfigured files (missing blockquote, no H2 sections, dump of 1,000+ URLs) get flagged with the specific fix.