Connect your client

Every client needs the same two things: the address https://first-signal-api.fly.dev/mcp and an API key sent as Authorization: Bearer <key>. Only the file or command that holds them differs. MCP overview lists what the tools do.

Before you start

Make a key

Open API keys in the app and select New key. Choose Read unless you want the assistant to create tests or start runs. Authentication has the steps.

Copy a snippet

The Key made dialog shows snippets for Claude Code, Cursor, Claude Desktop and curl with your key filled in. The snippets below cover the same clients and more, with sig_your_key as a stand-in. Swap in your own key, and do not commit it to a repository.

Set up your client

Claude Code
Claude Desktop
Cursor
VS Code
Other clients

Run this in a terminal.

Terminal

claude mcp add --transport http signal https://first-signal-api.fly.dev/mcp \
  --header "Authorization: Bearer sig_your_key"

By default Claude Code keeps the server for you, in the current project only. Add --scope user to use it in every project. Avoid --scope project: it writes the server, key included, to a .mcp.json file that you would share through git.Check the connection with claude mcp list, or run /mcp inside Claude Code. Then ask:

Use Signal’s whoami tool and tell me what this key can do.

Claude Desktop starts MCP servers as local programs from its config file, so it reaches the hosted endpoint through mcp-remote, a widely used npm package that speaks stdio to Claude Desktop and Streamable HTTP to Signal. Signal does not make or support it. It needs Node.js. Open Settings, then Developer, then Edit Config. That opens claude_desktop_config.json:

macOS: ~/Library/Application Support/Claude/claude_desktop_config.json
Windows: %APPDATA%\Claude\claude_desktop_config.json

Add the server, keeping any servers you already have.

claude_desktop_config.json

{
  "mcpServers": {
    "signal": {
      "command": "npx",
      "args": [
        "-y",
        "mcp-remote",
        "https://first-signal-api.fly.dev/mcp",
        "--header",
        "Authorization:${SIGNAL_AUTH}"
      ],
      "env": { "SIGNAL_AUTH": "Bearer sig_your_key" }
    }
  }
}

The header value sits in env so the argument has no space in it, which some systems mishandle. This is the same snippet the Claude Desktop tab in the app shows, with your key filled in. Quit Claude Desktop completely and open it again.

Cursor reads ~/.cursor/mcp.json for every project, or .cursor/mcp.json in one project.

.cursor/mcp.json

{
  "mcpServers": {
    "signal": {
      "url": "https://first-signal-api.fly.dev/mcp",
      "headers": { "Authorization": "Bearer sig_your_key" }
    }
  }
}

In a project file that you commit, keep the key out of the file. Cursor fills in environment variables.

.cursor/mcp.json

{
  "mcpServers": {
    "signal": {
      "url": "https://first-signal-api.fly.dev/mcp",
      "headers": { "Authorization": "Bearer ${env:SIGNAL_API_KEY}" }
    }
  }
}

Open the MCP section of Cursor’s settings and check that signal is on and lists its tools. Then ask the agent to call whoami.

VS Code reads .vscode/mcp.json in a workspace. Its file uses servers, not mcpServers. The inputs block makes VS Code ask for the key the first time the server starts and keep it out of the file, which you will probably commit.

.vscode/mcp.json

{
  "inputs": [
    {
      "type": "promptString",
      "id": "signal-api-key",
      "description": "Signal API key",
      "password": true
    }
  ],
  "servers": {
    "signal": {
      "type": "http",
      "url": "https://first-signal-api.fly.dev/mcp",
      "headers": { "Authorization": "Bearer ${input:signal-api-key}" }
    }
  }
}

Select Start above the server in the file, or run MCP: List Servers from the command palette. Enter your key when asked. The tools are available in Chat in agent mode.

Any client that supports MCP servers can connect. Which of these it takes depends on the client.A client that speaks Streamable HTTP and can send a header connects to the hosted endpoint. Most use a JSON file shaped like this. The key names vary a little, so check what your client calls the URL and headers.

mcp.json

{
  "mcpServers": {
    "signal": {
      "type": "http",
      "url": "https://first-signal-api.fly.dev/mcp",
      "headers": { "Authorization": "Bearer sig_your_key" }
    }
  }
}

Windsurf reads ~/.codeium/windsurf/mcp_config.json. For a remote server it may expect serverUrl where the file above has url. Signal has not tested it in Windsurf, so check Windsurf’s current documentation if it does not connect.A client that only starts local programs can use the same mcp-remote bridge as Claude Desktop above. Give it the command npx, the arguments -y mcp-remote https://first-signal-api.fly.dev/mcp --header Authorization:${SIGNAL_AUTH}, and SIGNAL_AUTH set to Bearer sig_your_key in its environment.A client that supports only the older SSE transport cannot use the hosted endpoint. The endpoint answers GET with 405, because it keeps no session and opens no stream.To test the endpoint without a client, ask it for its tool list.

Terminal

curl -sS https://first-signal-api.fly.dev/mcp \
  -H "Authorization: Bearer $SIGNAL_API_KEY" \
  -H "Content-Type: application/json" \
  -H "Accept: application/json, text/event-stream" \
  -d '{"jsonrpc":"2.0","id":1,"method":"tools/list"}'

If it does not work

What you see	Cause and fix
`401` with `mcp_unauthorized`, or “unauthorized” in the client	The key is missing, wrong or revoked. The header must read `Bearer` followed by the key, with one space. Check the key’s row on the API keys page
The write tools are not in the list	You are using a read key on the hosted endpoint, which hides them. Make a Write key if you want them
A tool answers `agent_required`	The key is for all agents. Pass `agentId` (ask the assistant to call `list_agents` first) or make a key tied to one agent
A tool answers `403` with `key_read_only`	A read key called a write tool. The hosted endpoint hides the write tools from a read key, so this is rare. Make a Write key if you need them
A tool answers `402` with `quota_exceeded`	Your plan’s simulated test calls for the period are used up, so a run was refused whole. Run fewer tests, upgrade, or wait for the reset. See Limits and quotas
A tool answers `429`	You reached a rate limit. Wait the number of seconds in `Retry-After`. See Rate limits
Claude Desktop shows the server as failed	Node.js is not installed or not on the path, or `SIGNAL_AUTH` does not read `Bearer` followed by the key. Open the MCP log from Settings, then Developer
The client cannot connect, or reports a `405`	The client expects the older SSE transport. Use a client or bridge that speaks Streamable HTTP

If you report a problem, include the requestId from the tool error.

Next steps

MCP overview

Every tool, example requests, and what a read or write key can do.

API reference

The same operations over plain HTTP.

​Before you start

​Set up your client

​If it does not work

​Next steps