Reletter MCP Server

Give AI agents and LLMs access to newsletter data from Reletter. Search 7M+ email newsletters across Substack, LinkedIn, Ghost, Beehiiv, and Kit. Fetch metadata, contacts, issues, and chart rankings.

This is a remote Model Context Protocol (MCP) server that connects AI assistants like Claude, ChatGPT, and Cursor to the Reletter API.

Use cases

• Read and analyze newsletter issues — pull the full body text of any indexed issue into your AI workflow

• Search and discover newsletters — find newsletters by topic, platform, or audience size

• Find newsletters to pitch — get your product, tool, or book featured. Filter by audience size, topic, or platform, then pull verified contact emails in one pass

• Build sponsorship, cross-promotion, and PR target lists — pull verified contacts and export them to your CRM

• Monitor brand or keyword mentions — track when your brand, competitors, or clients are mentioned across newsletters

• Track chart rankings — daily Substack / LinkedIn / Kit / Reletter chart data

Related MCP server: Ad Library MCP

Tools

• search_publications — Search for newsletters by topic, title, or author with filters

• search_issues — Full-text search across newsletter issue bodies

• autocomplete — Suggested keywords and matching newsletters for a partial query

• get_publication — Full metadata for a newsletter (subscribers, engagement, social, rankings, SEO reach)

• list_issues — Recent issues for a publication

• get_issue — A single issue with body text

• contacts — Email contacts, contact pages, social accounts for a newsletter

• chart_categories — Available chart platforms and categories

• chart_rankings — Latest chart rankings for a platform / category

• list_languages — Reference list of languages

• api_quota — Your API request quota and usage for the month

Setup

You need a Reletter API key. Get one here.

For autonomous agents that want to provision a key without a human in the loop, Reletter implements the Machine Payments Protocol. Hit POST https://api.reletter.com/api/payments/buy/ to get a 402 challenge, pay with a Stripe Shared Payment Token or with USDC on Tempo, and the response carries an API key tied to a freshly-provisioned account. Current bundle tiers: GET https://api.reletter.com/api/payments/bundles/. See https://reletter.com/llms-full.txt for the full flow.

ChatGPT

1. Go to Settings → Apps → Advanced settings and enable Developer mode

2. Click Create app

3. Enter Name: Reletter

4. Enter MCP Server URL: https://mcp.reletter.com

5. Click Create and enter your Reletter API key when prompted

Claude.ai

1. Go to Settings → Connectors

2. Click Add custom connector and enter name Reletter and MCP server URL https://mcp.reletter.com

3. Click Add and enter your Reletter API key when prompted

Claude Desktop

Add to your config file and restart Claude Desktop:

• macOS: ~/Library/Application Support/Claude/claude_desktop_config.json

• Windows: %APPDATA%\Claude\claude_desktop_config.json

{
  "mcpServers": {
    "reletter": {
      "url": "https://mcp.reletter.com"
    }
  }
}

Claude Code

Add to your project's .mcp.json:

{
  "mcpServers": {
    "reletter": {
      "type": "http",
      "url": "https://mcp.reletter.com"
    }
  }
}

Cursor

Go to Settings → MCP → Add new MCP server. Set type to URL and enter https://mcp.reletter.com.

If you want to fork or customize this MCP server for your own needs, here is how you can run or deploy it.

Prerequisites

• Node.js

• A Cloudflare account (for deployment)

Local dev

npm install
npm start

The server runs at http://localhost:8789. Test with the MCP Inspector:

npx @modelcontextprotocol/inspector@latest

Type-check

npm run type-check

Regenerate Cloudflare types

After changing wrangler.jsonc:

npm run cf-typegen