Connecting Clients – SignatureAPI Docs

Every MCP-compatible client needs the same two things: the server URL and a way to perform the OAuth sign-in flow. Once you provide the URL, the client handles discovery, registration, and the redirect to SignatureAPI for you.

https://mcp.signatureapi.com/mcp

The first time you connect, a browser window opens where you sign in to SignatureAPI and approve the connection. After that, the client refreshes its token automatically.

ChatGPT is the exception: SignatureAPI is a published app there, so you install it from the app directory instead of entering a URL. See ChatGPT.

Let your agent set itself up

If you already work inside an AI coding agent, you do not have to configure anything by hand. Paste this prompt into the agent and it reads this page, picks the section that matches itself, and does the setup:

Set up SignatureAPI for me. Read https://signatureapi.com/docs/ai-toolkit/mcp/connecting-clients.md
and follow the section for the agent you are running in. If I am working on a codebase, install the
SignatureAPI plugin (skills plus MCP server) rather than the MCP server alone. Ask me before opening
a browser for sign-in, and never print tokens or keys. When you are done, prove it works by listing
my 5 most recent test-mode envelopes, then tell me what you changed and how to undo it.

The prompt points at the Markdown version of this page, so the agent always gets the current instructions rather than a copy that goes stale.

One command for most coding agents

add-mcp configures the SignatureAPI MCP server in every supported agent it finds on your machine: Claude Code, Claude Desktop, Codex, Cursor, Gemini CLI, GitHub Copilot, VS Code, Windsurf, Zed, and others.

npx -y add-mcp https://mcp.signatureapi.com/mcp -g

Drop -g to configure only the current project instead of your user profile. The first time each agent uses the server, it opens the browser for sign-in.

One-click install

Install in Cursor

Opens Cursor and adds the SignatureAPI server to your MCP settings.

Install in VS Code

Opens VS Code and adds the server for Copilot agent mode.

After the client opens, confirm the server and complete the SignatureAPI sign-in when prompted.

Coding agents: install the plugin instead

An agent that writes integration code for you benefits from more than the MCP server. The SignatureAPI plugin bundles the server with three skills: one that designs how your app uses e-signatures, one that builds the signing flow end to end against test mode, and one that diagnoses a flow that misbehaves. Install the plugin and the agent gets all three in one step.

Claude Code
Codex
Cursor
Gemini CLI
Skills only

/plugin marketplace add signatureapi/skills
/plugin install signatureapi@signatureapi

The server is configured but unauthenticated until first use. When Claude Code reports Needs authentication, run /mcp and complete the sign-in flow.

Claude Code turns auto-update off for third-party marketplaces. To receive skill updates, run /plugin, open Marketplaces, select signatureapi, and choose Enable auto-update. The plugin is versioned by commit, so every change we publish is a new version. To update by hand instead:

/plugin marketplace update signatureapi
/plugin update signatureapi@signatureapi

codex plugin marketplace add signatureapi/skills
codex plugin add signatureapi@signatureapi
codex mcp login signatureapi

The last command runs the SignatureAPI sign-in in your browser. Check the result with codex mcp list.

To get the skills in any agent without configuring the MCP server:

npx skills add signatureapi/skills

This works in Claude Code, Codex, Cursor, Copilot, Amp, Antigravity, and every other agent the skills CLI supports.

Everything the plugin installs is public at github.com/signatureapi/skills, including what each skill can and cannot do.

Network access

Before configuring any client, make sure outbound HTTPS traffic to *.signatureapi.com is allowed on the network where the client runs. Corporate proxies, VPNs, firewalls, and AI sandbox environments that block these hosts will cause the connection or sign-in to fail.

Manual setup per client

Claude Desktop

Open Settings → Connectors → Add custom connector.
Name the connector “SignatureAPI” and enter the server URL above.
Save. A browser window opens for sign-in. Approve the connection.

The SignatureAPI tools become available in any conversation. You can pin frequently used envelopes from the side panel.

Claude.ai

From any chat, open Connectors → Add custom connector.
Enter the server URL above and save.
Complete the SignatureAPI sign-in when prompted.

Pure connector clients like Claude.ai do not execute code locally. When uploading documents, supply a publicly accessible URL on an allowlisted host (S3, Google Drive, Dropbox, and similar). See Uploading files.

ChatGPT

SignatureAPI is a published ChatGPT app. You install it from the app directory; there is no connector URL to paste and no developer mode to turn on.

In ChatGPT, open the app directory and search for SignatureAPI, or open the app page directly.
Click Connect and complete the SignatureAPI sign-in in the popup.

After that, mention SignatureAPI in a chat and ChatGPT calls the app’s tools.

ChatGPT cannot run a local PUT, so it does not use mint_upload_url. Attach a document to the chat and the app receives it through upload_file. You can also reference any document by a publicly accessible URL.

Claude Code

From the command line:

claude mcp add --transport http signatureapi https://mcp.signatureapi.com/mcp

Then, inside Claude Code, run /mcp and complete the sign-in flow. Envelopes become reachable through the @signatureapi resource picker.

Codex

From the command line:

codex mcp add signatureapi --url https://mcp.signatureapi.com/mcp

Then run codex mcp login signatureapi and complete the sign-in flow in your browser. Check the result with codex mcp list, which shows each server’s connection and authentication state.

Cursor

Use the one-click install above, or add the server to .cursor/mcp.json in your project (or ~/.cursor/mcp.json for every project):

{
  "mcpServers": {
    "signatureapi": {
      "url": "https://mcp.signatureapi.com/mcp"
    }
  }
}

Open Settings → MCP, and click the sign-in prompt next to the server to complete the OAuth flow.

VS Code

Use the one-click install above, or add the server to .vscode/mcp.json:

{
  "servers": {
    "signatureapi": {
      "type": "http",
      "url": "https://mcp.signatureapi.com/mcp"
    }
  }
}

Start the server from the MCP: List Servers command and complete the sign-in when VS Code asks. The tools appear in Copilot’s agent mode.

Gemini CLI

gemini mcp add --transport http signatureapi https://mcp.signatureapi.com/mcp

Then run /mcp auth signatureapi inside Gemini CLI to sign in.

Generic configuration

For any MCP client that accepts a Streamable HTTP server:

Field	Value
Transport	`http` (Streamable HTTP)
URL	`https://mcp.signatureapi.com/mcp`
Auth	OAuth 2.1 (the client handles it)

If the client does not implement OAuth Dynamic Client Registration, see Authorization for the discovery endpoints and the patterns available for service providers.

Verifying the connection

After connecting, ask the agent to call list_envelopes. A successful response with your account’s envelopes confirms the OAuth flow and account scoping are correct.

If the call returns “Application has been disconnected,” the connection was revoked from the dashboard. Reconnect by removing and re-adding the server in your client.