Integrations

Plays nice with your stack.

Letter sits at the centre of your lifecycle, not off to the side. Pipe contacts and events in from the tools you already run, or wire up anything you like with the API, SDKs, and webhooks.

New Run Letter from Claude, ChatGPT & Copilot

Zapier

Connect Letter to 6,000+ apps. Trigger Zaps when a contact is created or updated, and push contacts into Letter from anything Zapier touches.

Facebook Lead Ads

Pull leads from your Facebook lead forms straight into Letter and start a welcome sequence the moment they sign up.

Segment

Stream identified users and events from your Segment workspace so your campaigns fire on the data you already collect.

PostHog

Sync people and product events from PostHog to trigger lifecycle emails off real in-product behaviour.

Make

Automate workflows and route leads into Letter with Make scenarios, no code required.

Tally

Turn Tally form submissions into Letter contacts and kick off the right sequence automatically.

MCP server

Letter, inside your AI assistant.

Letter runs a remote MCP server. Add it to Claude, ChatGPT, or GitHub Copilot, sign in with your Letter account, and manage your email in plain English.

  • Write, test, and publish sequences
  • Draft, preflight, and schedule broadcasts
  • Build forms, segments, and lists
  • Look up, import, and tidy up contacts
  • Check sends, opens, and transactional deliveries
  • Edit templates, domains, and team settings
Read the MCP docs →
MCP server URL
https://mcp.letter.app/

Paste it into your assistant, then sign in with your Letter account. No API key to paste, nothing to install.

Connect it in a minute

One URL for every assistant. Pick yours:

Claude

claude.ai and Claude Desktop
  1. Open Customize → Connectors and choose Add custom connector.
  2. Name it Letter, paste the URL, and click Add.
  3. Click Connect, sign in to Letter, and approve.

Turn it on in any chat from the + menu. On Team and Enterprise, an owner adds it once in Organization settings → Connectors and members connect their own account.

ChatGPT

chatgpt.com
  1. Open Plugins, click +, and choose Add custom MCP server.
  2. Name it Letter, paste the URL as the Server URL, and pick OAuth.
  3. Click Create as a plugin, sign in to Letter, and approve.

Type @ in a chat and pick Letter. ChatGPT confirms with you before anything changes. Custom MCP servers depend on your plan and workspace settings.

GitHub Copilot

VS Code
  1. Run MCP: Add Server from the Command Palette and choose HTTP.
  2. Paste the URL and name the server letter.
  3. Sign in to Letter when VS Code opens your browser, then use it from Copilot Chat in agent mode.

Or commit it to .vscode/mcp.json so your whole team gets it:

{
  "servers": {
    "letter": {
      "type": "http",
      "url": "https://mcp.letter.app/"
    }
  }
}

Using something else? Cursor, Claude Code, and any client that supports remote MCP servers with OAuth connect the same way. In Claude Code, run this, then /mcp to sign in:

claude mcp add --transport http letter https://mcp.letter.app/
Try asking
  • Draft a three-email onboarding sequence for new trials.
  • How did last week's broadcast perform?
  • Build a segment of users who signed up but never invited a teammate.
  • Did jane@acme.com get her password reset email?
  • Add a waitlist form that drops signups into the Beta list.
Safe by design

  • Your sign-in, not a key

    You approve the connection on Letter's own consent screen. The assistant never sees an API key, can't create one, and can't touch billing.

  • Read-only if you prefer

    Choose read-only or read & write when you connect. Your role in the workspace still applies.

  • Asks before it sends

    Tools that email people or delete data are flagged, so your assistant checks with you first.

  • Disconnect anytime

    Settings → Connected apps lists every assistant you've connected. One click revokes it.

Don't see your tool?

Build it in minutes.

Letter is API-first. Identify a contact, track an event, or update a trait with a single call, then let sequences do the rest. When you'd rather react than poll, subscribe to webhooks and get pushed everything that happens.

Read the docs Browse the SDKs CLI reference

REST API

Identify contacts, track events, and manage lists from any backend.

CLI

Bootstrap your integration with npx @letterapp/cli and wire up contacts in minutes.

Typed SDKs

Official libraries so you ship in a few lines, not a few days.

Webhooks

Subscribe once and get pushed every send, open, and conversion.
Ready when you are

One hub for
every signal.

Free up to 1,000 contacts. No credit card. Connect a tool, fire an event, watch the sequence run.

Get started for free See pricing