robots.txt vs llms.txt: What AI Crawlers Actually Read
Two small text files, both meant to sit at the root of a domain, both aimed at automated visitors rather than humans — it's easy to assume llms.txt is just a newer version of robots.txt, or that having one makes the other redundant. They're not related that way. One is about permission, the other is about comprehension, and a site benefits from having both for entirely different reasons.
robots.txt: can a crawler visit this page at all
robots.txt is a decades-old convention, and it answers exactly one question: is this specific automated visitor allowed to request this specific URL? It says nothing about what the page contains — a search engine crawler, an AI training crawler, and a security scanner all read the same file and get the same yes-or-no answer for each path, based purely on the user-agent making the request.
llms.txt: what is this site actually about
llms.txt is a much newer, community-driven convention that answers a different question entirely: once a model is allowed to look at this site, what's the fastest, cleanest way for it to understand what's here? Instead of a page-by-page permission list, it's a single markdown file — a name, a short description, and a categorized index of the site's key pages, each with its own one-line summary. It's written for AI models specifically, not for traditional search crawlers, and it doesn't grant or restrict access to anything; a page can be freely crawlable and still not appear in an llms.txt index, or vice versa.
Why a model would prefer llms.txt over crawling normally
A model with a limited context window pays a real cost every time it has to fetch and parse a full HTML page — navigation markup, scripts, ads, and layout all take up space that could otherwise hold actual content. An llms.txt file front-loads a clean summary of the whole site in one small file, so a model can get oriented cheaply before deciding whether it's worth fetching any specific page in more depth. This is the same basic motivation as a sitemap helping a search engine discover pages faster — just optimized for a different kind of reader with a different kind of constraint.
Where AI-specific rules show up in robots.txt
robots.txt has picked up a secondary use recently: several AI companies' training crawlers respect specific named user-agents — GPTBot, ClaudeBot, Google-Extended, and others — which sites can Disallow individually if they want to opt out of that company's AI training crawl specifically, without affecting their regular search engine crawling. This is still squarely a permission decision, the same kind of rule robots.txt has always handled, just with a newer category of visitor.
Do you need both?
They're not redundant with each other. robots.txt is worth having on essentially every site, AI-focused or not, since it governs basic crawler access regardless of what's reading the file. llms.txt is worth adding once you actually want AI models to understand and reference your content well — a documentation site, a knowledge base, a product with an API — since its whole value is making that specific kind of comprehension cheaper and more accurate.
Generate both
FreeToolDev's robots.txt generator covers standard crawl rules plus one-click AI-crawler blocking, and the llms.txt generator turns a simple pasted list of your pages into a properly formatted, categorized index — both free, no signup, generated entirely in your browser.