llms.txt is a Markdown index for LLMs, placed at the site root. Where sitemap.xml is a machine-readable list of URLs, llms.txt describes — with one-line notes — what the site is and where to start reading.
In Astro you can generate it from Content Collections as an API route, so the post list never has to be hand-maintained. This post is the minimum setup for a bilingual (EN/JA) site: emit /llms.txt, /ja/llms.txt and /llms-full.txt from one renderer.
Up front: how much llms.txt actually helps AI-search traffic isn't a settled or measured thing yet. This is only about the implementation.
The minimal route
Astro's file-based API routes return text when you drop a .txt.ts file under src/pages/. Return a text/plain Response from a GET handler.
