---
title: Conformance
description: Basic, Standard, and Advanced conformance levels.
---

This document is normative.

## Conformance Levels

Three levels are defined: **Basic**, **Standard**, **Advanced**. A site claiming conformance MUST satisfy all checks at the claimed level and all checks at lower levels.

### Basic

A Basic conformant server:

- MUST serve a markdown twin at `<url>.md` for every HTML page that has one
- MUST set `Content-Type: text/markdown; charset=utf-8` on markdown responses
- MUST set `X-Markdown-Tokens` with a positive integer
- MUST set `X-Robots-Tag` containing `noindex` on markdown responses
- MUST set `Vary: Accept` on markdown responses
- MUST return a non-empty markdown body

### Standard

A Standard conformant server satisfies all Basic requirements PLUS:

- MUST honor `Accept: text/markdown` on the canonical HTML URL by serving the markdown twin
- MUST advertise the markdown twin via `Link rel="alternate" type="text/markdown"` on HTML responses
- MUST return `406 Not Acceptable` when no acceptable representation exists
- SHOULD set `Vary: Accept` on HTML responses

### Advanced

An Advanced conformant server satisfies all Standard requirements PLUS:

- MUST detect AI agent User-Agents from the [AI Agent Registry](/docs/spec/ai-bot-detection) and serve markdown to them by default
- MUST set `X-AEO-Version` advertising the implemented spec version
- SHOULD set `X-Content-Type-Options: nosniff`
- SHOULD publish `/llms.txt` per the [llms.txt extensions](/docs/spec/llms-txt-extensions)
- SHOULD include `.md` URLs in sitemap.xml OR publish `/sitemap.md`

## Test Suite

The reference test runner is [`@dualmark/cli`](/docs/packages/cli):

```bash
dualmark verify https://example.com/blog/hello
```

The runner produces a weighted score out of 100 (or 80 with `--skip-negotiation`). The score MUST be calculated as:

```
score = sum(weight for each passed check) / sum(weight for all applicable checks) * 100
```

A site is considered conformant at a given level when:

| Level | Threshold |
|---|---|
| Basic | >= 60% |
| Standard | >= 80% |
| Advanced | >= 95% |

## Check Catalogue

| ID | Description | Severity | Weight | Level |
|---|---|---|---|---|
| `md.fetch` | Markdown twin reachable (2xx) | required | 20 | Basic |
| `md.contentType` | `text/markdown; charset=utf-8` | required | 10 | Basic |
| `md.tokensHeader` | `X-Markdown-Tokens` integer >= 1 | required | 10 | Basic |
| `md.noindex` | `X-Robots-Tag` contains `noindex` | required | 10 | Basic |
| `md.vary` | `Vary` contains `Accept` | required | 10 | Basic |
| `md.body` | Non-empty markdown body | required | 10 | Basic |
| `md.aeoVersion` | `X-AEO-Version` advertised | recommended | 5 | Advanced |
| `md.nosniff` | `X-Content-Type-Options: nosniff` | recommended | 5 | Advanced |
| `html.reachable` | HTML URL reachable (2xx) | required | 5 | Standard |
| `html.linkAlternate` | HTML response has `Link rel="alternate"` | required | 10 | Standard |
| `html.vary` | HTML response `Vary: Accept` | recommended | 5 | Standard |
| `negotiation.botUa` | GPTBot UA receives markdown | recommended | 10 | Advanced |
| `negotiation.acceptHeader` | `Accept: text/markdown` receives markdown | required | 10 | Standard |
| `negotiation.notAcceptable` | Accept that excludes both -> 406 | recommended | 5 | Advanced |

## Independent Reimplementation

To verify a server conforms without relying on `@dualmark/cli`, the spec can be implemented in any language. A reference 50-line implementation in (any language) is in [the spec test suite](https://github.com/dodopayments/dualmark/tree/main/spec/conformance-tests) (forthcoming).

## Reporting Conformance

A site MAY display a conformance badge:

```
[![AEO Conformant](https://dualmark.dev/badge/standard.svg)](https://dualmark.dev/spec)
```

Badges are SHOULD-level claims. The authoritative measurement is the score from `dualmark verify`.