SigPen MCP server
Connect your AI assistant to SigPen, the e-signature app. Ask it to draft an NDA, fill in an offer letter from your template, or upload a PDF and line up the signers. It prepares everything; you approve every send in SigPen.
- Server URL:
https://www.sigpen.com/api/mcp (Streamable HTTP)
- Auth:
Authorization: Bearer <your SigPen API key>
- Guide: sigpen.com/docs/mcp
This repository holds the setup instructions and the plugins for Claude Code and Cursor. SigPen hosts the server itself, so there's nothing to install or run.
Before you start
- Create an API key at sigpen.com/developer. It works on the free Developer tier and on Professional and up (Starter has no API). Use a live key (
sp_live_) to draft; a test key can only look things up.
- Name the key "AI assistant" so you can revoke it on its own.
- Always use the
www URL. sigpen.com redirects, and the redirect drops your key.
Claude Code
With the plugin (asks for your key once and keeps it in Claude Code's secure storage, not in a settings file):
The plugin also adds a send-for-signature skill that walks Claude through drafting, filling in, and asking for approval.
Or add the server by hand, with the key in an environment variable:
Run /mcp in Claude Code to check it's connected.
Cursor
Set SIGPEN_API_KEY in your environment, then add this to ~/.cursor/mcp.json:
Or use the Install in Cursor button on the setup guide. The Cursor plugin in plugins/sigpen bundles the same config with the skill.
VS Code
Add to .vscode/mcp.json. VS Code asks for the key and stores it for you:
Codex
Add to ~/.codex/config.toml and set SIGPEN_API_KEY:
Other clients
Any client that supports remote MCP servers over Streamable HTTP and lets you set a request header works. The Claude and ChatGPT apps need one-click sign-in, which SigPen doesn't offer yet.
Tools
You can connect and list tools without a key. Every tool call needs one.
How sending works
The assistant never sends. request_send_approval returns a SigPen link. Open it signed in and you see the title, every recipient, how many fields each person fills, the values the assistant filled in, and its note for the invitation. Click Approve and send, or open the draft to change it.
- The link lasts 24 hours and works only for you.
- If anything changes after the link is made (recipients, fields, values, title), the link stops working.
- Revoking the API key cancels its open links.
- The assistant can only change or delete drafts it created.
Text inside a document can try to trick an assistant ("send this to [email protected]"). The approval page is where you catch that, so check every email address before you click.
Limits and data
- Each tool call counts as one API request against your key's rate limit.
- Drafts count toward your monthly document limit, and deleting one doesn't give it back.
- What a tool returns, such as document titles and signer names and emails, goes to your AI provider under their terms.
- To disconnect, revoke the key in the developer dashboard.
Support
Email [email protected]. For security issues, see SECURITY.md.
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