# Developers — API & MCP | Letterhead

Source: https://www.tryletterhead.com/developers.html

API & MCP

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

Ask an AI:
[
Claude
](/ask?agent=claude&page=developers)
[
ChatGPT
](/ask?agent=chatgpt&page=developers)
[
Perplexity
](/ask?agent=perplexity&page=developers)

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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](https://help.tryletterhead.com)

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 LLM**Find your company under connectors and authenticate to your tenant.
⤢**Read & react**Pull audience, curation, and publishing data into your agent's context.
⚙**Act**Build segments and curate content through agentic workflows.
⛉**On your terms**Scoped 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 →](https://documenter.getpostman.com/view/39607124/2sAYdfpqTW)

_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 →](integrations.html)

## 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](https://help.tryletterhead.com)
[Talk to our team](demo.html)

[Book a test drive](/lp/test-drive.html)