API & MCP

Tools that work the way you work, where you work.

Letterhead is API-first, with a native MCP server. Access and control every aspect of your newsletter operation through API, webhooks, AI LLMs, and Zapier — no matter your stack and how you work, Letterhead makes it easy to sync data and automate workflows.

Read the docs

curl — Letterhead v3 API

# Add or update a subscriber — all fields
curl -X POST "https://<tenant>.api.tryletterhead.com/api/v3/audience" \
  -H "Api-Key: $LH_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{ "email": "reader@example.com", "fields": { "tier": "vip" } }'

# Curate with AI by subject (beta)
curl -X POST "https://<tenant>.api.tryletterhead.com/api/v3/curate-ai" \
  -H "Api-Key: $LH_API_KEY" \
  -d '{ "subject": "local elections", "channel": "daily" }'

# …or skip the API: connect your tenant to Claude as an MCP connector.

Illustrative — see the API reference for exact endpoints. Base URL is per-tenant.

Native MCP server

Build and manage your newsletters from your LLM of choice.

Connect your Letterhead company to any MCP-compatible agent as a connector. Your AI tools authenticate to your Letterhead instance and can query data, build segments, curate content, and run many of the same operations your team uses in-app. Agentic operations, on your terms.

◈

Connect your LLMFind your company under connectors and authenticate to your tenant.

⤢

Read & reactPull audience, curation, and publishing data into your agent's context.

⚙

ActBuild segments and curate content through agentic workflows.

⛉

On your termsScoped to your tenant, behind your auth and platform controls.

REST API

Powerful, easy APIs for everything.

A versioned (v3) REST API with API-key auth. Generate keys in Settings → API Keys, and build against the data your newsletter operation runs on.

API reference →

Webhooks

Act the moment it happens.

Subscribe to the events that matter and push them anywhere.

✓Audience member created or updated ✓Audience member unsubscribed ✓Newsletter published ✓Newsletter scheduled ✓Newsletter sent ✓Curation created or updated ✓Promotion campaign created, updated, or status changed

No-code with Zapier

Not a developer? No problem.

Connect Letterhead to thousands of apps with Zapier — sync your CRM, pull content from your CMS or Slack, route survey data into audience profiles — no code required.

CRM→CMS / Slack→Letterhead

Letterhead→Survey tools→Audience profiles

Integrations

Wired into the tools your operation already runs on.

Beyond the API, MCP, webhooks, and Zapier, Letterhead works alongside your existing ESP, CRM, CMS, and content tools — Mailchimp, Iterable, HubSpot, Salesforce, SparkPost, WordPress, Slack, and more.

Explore all integrations →

Build your email operation any way you like.

Read the docs to start, or talk to us about API and MCP access and custom integration options.

Read the docs Talk to our team

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