llms.txt Checker

What is an llms.txt checker?

An llms.txt checker is a tool that validates the llms.txt file on your website so AI systems can read your content correctly. The llms.txt standard, proposed in 2024, is a markdown file placed at the root of your domain that gives large language models a curated map of your most useful pages. The tool parses that file and flags anything that does not match the spec.

Because the format is still new, small mistakes are easy to make — a missing title, a broken link, or a malformed section. Running an llms.txt checker before you publish means AI crawlers and assistants get a clean, well-structured file instead of one they cannot parse. Think of it as a linter for the file that tells AI which pages on your site matter most.

How to check your llms.txt file online

You can check llms.txt two ways with the tool above:

1. Paste your file. Copy the contents of your llms.txt into the box and press “Check llms.txt”. Validation runs instantly in your browser.
2. Check by URL. Enter your domain and the checker fetches /llms.txt for you, then validates it. This is the fastest way to check llms.txt on a site that is already live.

Either way, the result shows a 0–100 health score plus a list of errors, warnings, and suggestions. If you are still wondering how to check llms.txt at all, the “Load sample” button drops in a valid example you can study and edit.

What this llms.txt validator checks

Acting as a full llms.txt validator, the tool checks every part of the file against the standard:

• H1 title. The file must start with a single # Title line naming your site or project.
• Summary blockquote. A > summary line right after the title is recommended so AI grasps your site at a glance.
• Link sections. Each ## Section should contain markdown links in the - [name](url): description format.
• Valid URLs. Every link is checked for a valid https:// URL or a site-relative path.
• Optional section. The validator confirms the ## Optional block, whose links can be skipped, comes last.

Why use an llms.txt checker?

As AI assistants become a real source of traffic, an llms.txt file helps tools like ChatGPT, Claude, Perplexity, and Gemini find and cite the right pages on your site. But a file with errors can be ignored entirely. Using the checker turns a guess into a quick, confident check that your file is correct before AI ever reads it.

The checker is also a fast way to learn the format. The health score and inline suggestions teach you what a strong file looks like, so each time you run the tool your file gets a little better — better titles, clearer summaries, and descriptive links that help AI understand your content.

When should you run the llms.txt checker?

Run a check the first time you create the file, since the format is easy to get subtly wrong. After that, re-check whenever your site changes in a way that affects the pages you point AI to — a docs restructure, a new product section, renamed URLs, or removed pages that would now leave dead links in your file. A quick check after each of these keeps the file accurate.

It is also worth checking other sites you admire: enter their domain to fetch and inspect a real, working file, then borrow the structure for your own. Many teams add a check to their release routine so the file is validated alongside the rest of the site, the same way they would lint code or test links before shipping. Treating the file as something you maintain, not set once and forget, is the difference between an llms.txt that helps AI and one that quietly rots.

llms.txt format and a sample template

A valid file is short and readable. It opens with an H1 title, an optional one-line summary blockquote, optional context, and one or more link sections. Here is the shape the checker expects:

# Example Project

> A one-sentence summary of the site for AI systems.

## Docs
- [Getting started](https://example.com/start): setup guide
- [API reference](https://example.com/api): full reference

## Optional
- [Changelog](https://example.com/changelog): release history

Paste a template like this into the checker, edit it for your own site, and re-run it until the score is clean.

llms.txt checker vs llms.txt validator

People search for an “llms.txt checker”, an “llms.txt validator”, an “llms checker”, and even an “llm.txt checker” — but they all want the same thing: confirmation that the file is correct. There is no real difference between checking and validating here. This tool does both jobs, so whether you call it a checker or a validator, you get the same thorough result.

That is why we built one page instead of separate tools. The tool validates structure and links, scores the file, and previews how it parses — covering the checker and validator use cases together.

Common llms.txt errors and fixes

The most common error the checker catches is a missing or duplicated H1 title — every file needs exactly one. Next are malformed links: a section heading with no links under it, or a link that is not written as - [name](url). Broken or relative URLs that should be absolute are flagged as errors too.

Warnings usually mean a missing summary blockquote or a section without any links, while suggestions nudge you to add descriptions to each link. Fix the errors first, then clear the warnings, and run the llms.txt checker again to confirm a clean, high score.

Is the llms.txt checker private and free?

Yes. The tool is completely free with no signup and no limit. When you paste text, validation runs entirely in your browser. When you enter a URL, only that public file is fetched server-side — nothing about your file is stored by JustTools.

Frequently Asked Questions

What is an llms.txt checker?

An llms.txt checker is a free tool that validates your llms.txt file against the official spec. Paste your file or a URL and the checker reports missing titles, broken links, and formatting issues so AI systems can read your site correctly.

How do I check my llms.txt file?

Paste the contents of your llms.txt file into the checker above, or enter your site URL to fetch it automatically. The validator parses the file instantly and shows errors, warnings, suggestions, and a 0–100 health score.

Is this llms.txt checker the same as an llms.txt validator?

Yes — "llms.txt checker" and "llms.txt validator" describe the same job: checking that your llms.txt follows the standard. This tool does both, validating structure, links, and formatting in one place.

Where should my llms.txt file live?

Place it at the root of your domain, for example https://example.com/llms.txt. That is also the path the checker fetches when you enter a URL.

Does the llms.txt checker upload my file?

When you paste text, validation runs entirely in your browser and nothing is uploaded. When you enter a URL, the tool fetches that public file server-side to avoid browser cross-origin limits, then checks it.

What does the llms.txt checker validate?

It checks for a single H1 title, a summary blockquote, properly formatted '##' link sections, valid link URLs, link descriptions, and correct placement of the optional section — then scores the file out of 100.

How is llms.txt different from robots.txt?

robots.txt tells crawlers which URLs they may access. llms.txt instead gives LLMs a curated, markdown map of your most useful content. Use this checker for llms.txt and your usual tooling for robots.txt.