---
title: llms.txt validator — 10 checks against the llmstxt.org spec
description: The most thorough llms.txt validator. 10 checks against the llmstxt.org specification — including HTTP Content-Type and the llms-full.txt companion that most validators skip.
last_updated: 2026-05-11
canonical_url: https://agent-ready.dev/llms-txt-checker
---

# llms.txt validator — 10 checks against the llmstxt.org spec

> The most thorough llms.txt validator on the web. 10 checks against the llmstxt.org specification — including the HTTP Content-Type header and the llms-full.txt companion file that most validators skip.

## What is llms.txt?

A Markdown file served at `/llms.txt` that gives AI systems a curated, plain-text map of a website's most important content. Acts as a machine-readable index — similar to `sitemap.xml` for search engines, but optimised for AI agents and language models. Proposed by Jeremy Howard (Answer.AI) in late 2024.

## Why should I add llms.txt to my site?

Without `/llms.txt`, LLMs scrape and guess at what your site is for, which hurts citation accuracy. With it, ChatGPT-style agents get a curated, link-rich index to the pages you actually want them to cite — cheaper than rewriting your whole site for LLM-friendly navigation, and the only standard currently in wide use across docs sites.

## What does the llms.txt validator check?

Ten checks against the llmstxt.org specification:

- File accessible at `/llms.txt` (HTTP 200)
- Starts with an H1 heading (project/site name)
- Contains valid, parseable Markdown
- Has a blockquote summary directly below the H1
- Includes H2 sections with file lists
- Links use the `[name](url)` format
- Linked URLs are accessible
- Optional section format used correctly
- Content-Type is `text/plain`
- `llms-full.txt` companion file is available

## How does this compare to other llms.txt validators?

The [llmstxt.org spec](https://llmstxt.org) describes eight structural rules, plus implied HTTP semantics. Most validators in circulation — including [llmstxtchecker.net](https://llmstxtchecker.net) — cover the structural rules and follow the linked URLs. Agent Ready does that too, and adds two checks the spec implies but most tools skip: the HTTP `Content-Type` header and the `llms-full.txt` companion file.

| Check | Agent Ready | Typical other validators |
|---|---|---|
| File accessible at /llms.txt | yes | yes |
| H1 heading present | yes | yes |
| Valid, parseable markdown | yes | yes |
| Blockquote summary | yes | yes |
| H2 sections with file lists | yes | yes |
| Link format [name](url) | yes | yes |
| Linked URLs return 200 | yes | yes |
| Optional section used correctly | yes | varies |
| **Content-Type: text/plain** | **yes** | rarely checked |
| **llms-full.txt companion** | **yes** | rarely checked |
| **Folded into full agent-readability scan** | **yes** | no |

Information based on the public copy at [llmstxtchecker.net](https://llmstxtchecker.net) as of 2026-05-11. The Content-Type and llms-full.txt checks are part of our 10 llms.txt rules ([methodology](https://agent-ready.dev/methodology#llmstxt-checks)); the full-site scan adds 49 more checks across page metadata, site discovery files, and agent-protocol manifests.

## Minimal valid example

```markdown
# Acme Cloud Widgets

> Widgets-as-a-service for serverless apps. Deploy in one command.

## Docs

- [Getting Started](https://acme.dev/docs/start.md): Zero to deployed in 60s
- [API reference](https://acme.dev/docs/api.md): REST endpoints and auth

## Examples

- [Node.js quickstart](https://acme.dev/examples/node.md)
```

H1 title, blockquote summary, H2 sections with `[name](url)` links. That's the whole spec.

## Specification

- [llmstxt.org](https://llmstxt.org) — proposal by Jeremy Howard (Answer.AI)
- [Format reference](https://llmstxt.org/#format)

---

Validate your llms.txt: <https://agent-ready.dev/llms-txt-checker>

Step-by-step guide: [How to add an llms.txt file to a Next.js site](https://agent-ready.dev/how-to-add-llms-txt-to-nextjs)

## Sitemap

See the full [sitemap](https://agent-ready.dev/sitemap.md) for all pages on agent-ready.dev.