Updated
Definition
llms.txt is an emerging web convention in which a site publishes a markdown file at its root that gives AI systems a curated summary of the site and links to its most useful content in a form language models parse cleanly.
The convention exists because HTML is a bad interface for models: navigation chrome, scripts, and layout markup dilute the content an AI system is actually trying to read. Where robots.txt tells crawlers what they may access, llms.txt tells AI systems what matters and where, in plain markdown, typically an overview plus an annotated link list, sometimes with expanded full-text companion files.
It is a convention, not a standard: adoption among AI providers is uneven and publishing the file guarantees nothing about how any given system will use it. The pragmatic case is cost and control: the file is cheap to maintain, and for API-shaped products it is a natural place to point models at documentation and machine-readable surfaces, so an assistant asked about your product summarizes from your curated map rather than from scraped page fragments.
No, the three answer different questions. robots.txt governs crawler access, sitemap.xml enumerates URLs for indexing, and llms.txt curates meaning: what the site is and which pages best explain it, in a format models ingest without HTML noise.
The cost is one maintained markdown file, and the downside is nil. For developer products the stronger argument is adjacent anyway: making your documentation genuinely machine-readable helps every AI surface that reads it, llms.txt aware or not.
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