The Thirdraft MCP server

More and more of what goes out under your name is written by an agent: emails, docs, Slack updates, PR descriptions. The Thirdraft MCP server lets your agent run that text through your own voice before it goes out. Your voice is learned from things you actually wrote. Facts, names and numbers stay as they were.

You need a Thirdraft account with a few writing samples. Free accounts get 3 rewrites a week to try it, shared with the website and the Chrome extension.

Server URL

https://api.thirdraft.com/mcp

It works with Claude (desktop and web), Claude Code, Cursor, VS Code, and any MCP client that supports remote servers with OAuth. Each one signs you in to Thirdraft in your browser the first time, and you click Allow. No keys to copy.

Connect Claude

In Claude, open Settings, then Connectors, then Add custom connector. Name it Thirdraft, paste the server URL above, and click Connect.

Connect Cursor or VS Code

Or add it yourself, in ~/.cursor/mcp.json:

{
  "mcpServers": {
    "thirdraft": { "url": "https://api.thirdraft.com/mcp" }
  }
}

Connect Claude Code

Run this once, then type /mcp in Claude Code and sign in:

claude mcp add --transport http thirdraft https://api.thirdraft.com/mcp

Other clients and API keys

Any MCP client that supports remote servers with OAuth can connect to the server URL. If yours can't sign in, create an API key under Connect an agent at thirdraft.com/app and send it as Authorization: Bearer <key>.

Zapier, Make and n8n

Automations call Thirdraft with a web request and an API key. Create a key under Connect an agent at thirdraft.com/app, then add a step. In Zapier that's Webhooks by Zapier, Custom Request. In Make it's the HTTP module. In n8n it's the HTTP Request node.

Method: POST. URL:

https://api.thirdraft.com/mcp

Headers:

Authorization: Bearer YOUR_API_KEY
Content-Type: application/json
Accept: application/json, text/event-stream

Body (put your earlier step's text in text):

{"jsonrpc":"2.0","id":1,"method":"tools/call","params":{"name":"rewrite_in_my_voice","arguments":{"text":"TEXT TO REWRITE","context":"email to a client"}}}

The rewrite comes back at result.content[0].text. Use it in your next step, like a Gmail draft or a Slack message.

Each run uses one rewrite from your plan. Text with quotes or line breaks has to be escaped for JSON. Make and n8n do that for you if you build the body as JSON fields instead of raw text.

Tools

Agents can't delete your samples or read them back out. You manage samples at thirdraft.com/app.

How the voice profile works

Your samples

It all starts from things you wrote yourself: emails, messages, docs, PR descriptions. When you save a sample, Thirdraft labels it with the kind of writing and who it's for. It also stores an embedding of it so it can find similar writing later.

The closest samples for each draft

When your agent sends a draft, Thirdraft labels the draft the same way and picks the 5 samples of yours closest to it in that situation. A Slack message to a coworker gets your messages to coworkers, not your design docs. If nothing fits, it uses your newest samples.

A short style guide

Once you have about a page of samples (around 2,500 characters), Thirdraft boils them down into a short style guide: sentence length and rhythm, word choice, punctuation habits, tone and phrases you repeat. Every rewrite gets the guide and the closest samples together.

Careful updates

The guide isn't rebuilt on every rewrite. It only gets rebuilt after about 8,000 more characters of new samples, so one odd email doesn't change how you sound. Agent rewrites are never saved as samples, so your agent's writing never teaches Thirdraft what you sound like. Samples an agent adds are marked "via agent" so you can review them.

Make it automatic

Agents use Thirdraft when they're told to. Add this to your agent's instructions, like Claude Code's CLAUDE.md, a Cursor rule, or a Claude project's instructions:

Before publishing anything you write for me (emails, docs, messages, posts, PR descriptions), run it through Thirdraft's rewrite_in_my_voice tool and use the result.

Then try something like:

Draft an email to Dana at Northwind: the launch is moving from May 12 to May 19 because our payments vendor is running late. The pilot stays at 50 seats, and we'll cover the extra week of support at no cost. Keep it short and honest, then run it through Thirdraft so it sounds like me before I send it.

New to Thirdraft? Give it your voice first:

Here are three emails I wrote. Add them to Thirdraft as writing samples: ...

Limits

• 150 rewrites a week on Personal and 375 on Pro, shared with the website and extension. Up to 10 a minute through agents, and up to 8,000 characters each.
• 20 samples a day through agents, up to 2,000 characters each.
• Rewrites reset every Monday, samples at midnight UTC. See pricing and fair use.

Your data

Text your agent sends is handled exactly like text you rewrite yourself. It's sent to Anthropic to write the rewrite and to Voyage AI to find your closest samples, and it isn't stored. Full details are in the privacy policy.

If something doesn't work

• "Thirdraft doesn't know this person's voice yet": add a few things you've written, at thirdraft.com/app or with add_writing_sample.
• "Used its 3 free rewrites for this week": they come back on Monday, or see pricing.
• Sign-in doesn't finish: remove Thirdraft from your agent, add it again, and sign in with the same account you use on the website.
• To disconnect, remove Thirdraft in your agent's settings. API keys can be revoked at thirdraft.com/app.

Anything else: support@thirdraft.com. For a walkthrough using it on pull requests, see AI PR descriptions that sound like you. For why this isn't a humanizer, see Thirdraft vs AI humanizers.

Questions