NewsletterFIT MCP server

Search newsletters, sponsors, topics, companies and people across 89,000+ Substack and beehiiv newsletters from any MCP client. The tools are read-only, except the Enterprise data export. Agents can read this page as Markdown.

• Endpoint: https://newsletterfit.com/mcp (streamable HTTP, JSON-RPC 2.0, stateless, POST only)
• Auth: OAuth 2.1 sign-in (Claude.ai, ChatGPT), or Authorization: Bearer nf_live_… API key
• Tools: 17

Get started

1. Use a plan with API access: Pro, Intelligence or Enterprise.
2. For a connector that signs in (Claude.ai, ChatGPT), you only need the URL. For an API key, open Billing → API access and create one; it is shown once.
3. Add the server to your client, then ask: “What tools do you have from NewsletterFIT?”

Claude.ai and Claude Desktop (connector)

Settings → Connectors → Add custom connector. Paste the URL, then sign in to NewsletterFIT and click Allow. No API key needed:

https://newsletterfit.com/mcp

ChatGPT

Add a custom connector (developer mode) with this URL and OAuth authentication, then sign in to NewsletterFIT and allow access:

https://newsletterfit.com/mcp

Claude Code

Run once in a terminal:

claude mcp add --transport http newsletterfit https://newsletterfit.com/mcp \
  --header "Authorization: Bearer nf_live_YOUR_KEY"

Cursor

Add to ~/.cursor/mcp.json (or .cursor/mcp.json in a project):

{
  "mcpServers": {
    "newsletterfit": {
      "url": "https://newsletterfit.com/mcp",
      "headers": { "Authorization": "Bearer nf_live_YOUR_KEY" }
    }
  }
}

Claude Desktop with an API key

To use an API key instead of signing in, run mcp-remote (needs Node.js). Add to claude_desktop_config.json, then restart Claude:

{
  "mcpServers": {
    "newsletterfit": {
      "command": "npx",
      "args": ["-y", "mcp-remote", "https://newsletterfit.com/mcp",
               "--header", "Authorization:Bearer nf_live_YOUR_KEY"]
    }
  }
}

Any client or curl

Streamable HTTP, JSON-RPC 2.0. Send both Accept types or the server answers 406:

curl -X POST https://newsletterfit.com/mcp \
  -H "Authorization: Bearer nf_live_YOUR_KEY" \
  -H "Content-Type: application/json" \
  -H "Accept: application/json, text/event-stream" \
  -d '{"jsonrpc":"2.0","id":1,"method":"tools/list"}'

Authentication and scopes

OAuth sign-in. Connectors discover the sign-in server from the 401 challenge (RFC 9728), register themselves (RFC 7591) and use authorization code with PKCE. You sign in to NewsletterFIT and approve the mcp:read scope, which allows every read tool on your plan but never create-export-tool. Your account needs a confirmed email. Access tokens are short-lived and bound to the /mcp resource; refresh tokens rotate.

API keys. Keys look like nf_live_<keyId>_<secret>. New keys get search:read, publications:read and entities:read, which can call every tool except create-export-tool; that one needs exports:write (or mcp:use, which allows every tool). Plan features still apply: list-alerts-tool needs a plan with alerts, and exports need Enterprise.

Limits

MCP and the REST API share one monthly quota per account, reset on the 1st (UTC). Failed tool calls are not counted. Each tool counts against one meter, shown below.

Rate limit: 90 requests a minute per key, shared with REST, reported in RateLimit-* headers. Every successful tool result includes a quota object with used, limit, remaining and resets_at.

Ids

Results use typed ids: nl_ newsletter, is_ article, sp_ sponsor, tp_ topic, en_ other entity. Tool arguments accept the typed form or the bare number.

Tools

Search

Newsletters

Articles

Sponsors, topics and entities

Your account

Data export

Errors

Guidance for agents

• Search first, then open one result: search-newsletters-tool, then get-newsletter-tool or get-newsletter-intel-tool.
• Use get-newsletter-intel-tool when comparing many newsletters; it is the smallest profile.
• Keep limit small (5–20). Ask for more pages only when the user needs them.
• Every successful result includes quota (used, limit, remaining, resets_at). Check remaining before long loops.
• Ids are typed (nl_ newsletter, is_ article, sp_ sponsor, tp_ topic, en_ entity). Pass them back exactly as returned; bare numeric ids also work.
• Audience figures are what the platform shows publicly, often rounded. Say so when you quote them.
• When a tool returns isError, read the code and message. Retrying the same call will fail the same way.

Common workflows

• Find newsletters to sponsor: search-newsletters-tool (topic) → get-newsletter-intel-tool for each candidate → get-newsletter-tool for the shortlist.
• Check who a brand sponsors: search-sponsors-tool (brand) → get-sponsor-tool (slug).
• Track a company in the press: search-entities-tool (type company) → get-entity-tool → get-article-tool for the mentions that matter.
• Map a topic: search-topics-tool → get-topic-tool → get-newsletter-intel-tool for the top newsletters.
• Spot growth: get-rising-newsletters-tool → get-newsletter-tool for the ones in the user's market.

Not supported yet

• Creating or editing alerts and watchlists; use the app.
• MCP resources and prompts; tools only.

Machine-readable

• This page as Markdown
• Tool schemas (JSON)
• Agent authentication
• Agent identity (AID)
• MCP server card
• REST API reference
• REST API reference as Markdown
• OpenAPI 3.1

Support: support@newsletterfit.com