@markdown-for-agents/fastify

Fastify plugin for markdown-for-agents — a runtime-agnostic HTML to Markdown converter built for AI agents.

markdown-for-agents converts HTML to clean, token-efficient Markdown for AI agents — typically saving 80–90% of tokens. This package adds automatic content negotiation to your Fastify app via Accept: text/markdown. Try the playground to see the core conversion in action.

Add one line to your Fastify app and AI agents get clean, token-efficient Markdown instead of HTML. Normal browser requests pass through untouched.

How it works

The plugin uses content negotiation. When a client sends Accept: text/markdown, HTML responses are automatically converted to Markdown. The response includes:

• Content-Type: text/markdown; charset=utf-8
• x-markdown-tokens header with the token count
• ETag header with a content hash for cache validation
• Vary: Accept header so CDNs cache HTML and Markdown separately
• content-signal header with publisher consent signals (when configured)

Install

npm install @markdown-for-agents/fastify markdown-for-agents

markdown-for-agents is a peer dependency — you may already have it installed.

Usage

import Fastify from 'fastify';
import { markdown } from '@markdown-for-agents/fastify';

const fastify = Fastify();
fastify.register(markdown({ extract: true }));

fastify.get('/', async (request, reply) => {
    reply.type('text/html');
    return '<h1>Hello</h1>';
});

fastify.listen({ port: 3000 });

# Normal HTML response
curl http://localhost:3000

# Markdown response for AI agents
curl -H "Accept: text/markdown" http://localhost:3000

Full working example: See examples/fastify/ for a complete Fastify app with integration tests.

Options

Accepts all markdown-for-agents options:

fastify.register(
    markdown({
        // Strip nav, ads, sidebars, cookie banners
        extract: true,

        // Resolve relative URLs
        baseUrl: 'https://example.com',

        // Remove duplicate content blocks
        deduplicate: true,

        // Custom token counter (e.g. tiktoken)
        tokenCounter: text => ({ tokens: enc.encode(text).length, characters: text.length, words: text.split(/\s+/).filter(Boolean).length }),

        // Publisher consent signal header
        contentSignal: { aiTrain: true, search: true, aiInput: true }
    })
);

Other frameworks

| Package | Framework | | -------------------------------------------------------------------------------------------- | -------------------------------------------- | | @markdown-for-agents/express | Express | | @markdown-for-agents/hono | Hono | | @markdown-for-agents/nextjs | Next.js | | @markdown-for-agents/web | Web Standard (Cloudflare Workers, Deno, Bun) |

License

MIT