Signal Cli

An MCP server that lets AI assistants (Claude Code) propose sending Signal messages — but nothing is ever sent without explicit human approval. The security guarantee is hard-wired into the architecture: the only path to sending a message goes through signal-client.ts, which is called only after a Decision is approved in approval-core.ts. No tool can bypass this mechanism — if the user rejects or the timeout expires, the message is never sent.

Supported client

• Claude Code — supported. You must set "timeout": 900000 in the configuration; otherwise Claude Code will cut off the call during long approvals.
• Claude Desktop — not supported. It has a hard-coded 60 s tool timeout that cannot be reconfigured.

Tools

Tool	Description
proposeSignalMessage	Proposes sending a message to an individual
proposeSignalGroupMessage	Proposes sending a message to a group
proposeSignalGroupCreation	Proposes creating a new group

Recipients, group targets, and group members may be given either as a contact/group name or as an E.164 number / group.<id>. The server resolves names against signal-cli's contacts and groups (exact, case-insensitive match); if nothing matches — or several do — the call fails with the candidates so the assistant can disambiguate. The approval GUI always shows the resolved Name (number) so you verify the real recipient before approving.

Setup

1. Start signal-cli-rest-api

docker compose up -d

The Docker Compose file is included in the repository and starts signal-cli-rest-api on port 8080.

2. Link a Signal account

Open in your browser:

http://localhost:8080/v1/qrcodelink?device_name=signal-cli-mcp

Scan the displayed QR code in the Signal app (Settings → Linked Devices). Verify the link:

curl http://localhost:8080/v1/accounts

The output should contain your phone number.

3. Build the project

npm install && npm run build

4. Configure Claude Code

Copy .mcp.json.example to .mcp.json in your project folder (Claude Code loads it from there) and edit:

• /ABSOLUTE/PATH/signal-cli-mcp/dist/index.js → the real absolute path on your machine
• SIGNAL_ACCOUNT → your phone number in E.164 format (e.g. +1234567890)

Leave the other variables as-is or adjust as needed. timeout: 900000 is required — without it Claude Code will cut off the call if approval takes longer than 60 seconds.

5. Open the approval GUI

Keep a browser tab open at http://localhost:8088. Proposed messages appear there for approval. Without the tab open approval still works, but you won't see a live preview (you'll get the result when you visit the URL).

Usage

In Claude Code, type something like: "Send John a message that I'll arrive at 6 PM."

Claude Code will call proposeSignalMessage. The proposal appears at http://localhost:8088. Click Approve to send, Reject to decline (with an optional reason), or Edit + Approve to modify the text before sending.

For a detailed walkthrough see docs/MANUAL.md.

Push notifications (optional)

So you don't have to watch the GUI tab, the server can send an ntfy push (macOS + iOS apps) whenever a proposal arrives. Set these env variables:

• NTFY_TOPIC — the ntfy topic to publish to (subscribe to it in the ntfy app). Enables notifications.
• NTFY_BASE_URL — ntfy server (default https://ntfy.sh; point this at a self-hosted server later).
• GUI_PUBLIC_URL — where you reach the GUI; used for the tap-through and the action buttons (see below).

With NTFY_TOPIC set, every new proposal triggers a push with the recipient and a text preview. When GUI_PUBLIC_URL is also set, the notification is actionable:

• tapping the notification opens the GUI directly (ntfy Click),
• Approve / Reject buttons appear in the notification and POST straight to the GUI's /action endpoint — one-tap decisions without opening anything; Open GUI is offered for edits.

Delivery is best-effort — a failed or unconfigured push never blocks approval. Notifications go to ntfy only; they never touch signal-cli.

Privacy note: on the public ntfy.sh, the topic name is a shared secret and the notification content (recipient, text preview) transits ntfy.sh. For a private setup, self-host ntfy and point NTFY_BASE_URL at it — planned as a follow-up.

Remote deployment (Docker MCP gateway + Tailscale)

When the server runs remotely (e.g. inside a Docker MCP gateway rather than launched locally by Claude Code):

• Transport: the MCP gateway exposes the server over HTTP/SSE; the server itself stays stdio — no code change. Point your MCP client at the gateway.
• Reaching the GUI: expose the GUI port over your Tailscale network, e.g. tailscale serve --bg <GUI_PORT>, and set GUI_PUBLIC_URL to the resulting MagicDNS URL (e.g. https://signal-mcp.<tailnet>.ts.net/). Tailscale is the access boundary — only your devices can reach it, so the GUI needs no extra login. Because your phone is on the tailnet too, tapping the notification (or its Approve/Reject buttons) reaches the GUI straight from the iPhone.
• Egress: the container needs outbound access to the ntfy server and to signal-cli-rest-api.

Releasing (npm)

The package is published to npm automatically by GitHub Actions (.github/workflows/publish.yml) when a version tag is pushed, using npm Trusted Publishing (OIDC) — no token secret, and provenance is generated automatically.

One-time setup on npmjs.com (package → Settings → Trusted Publisher): add a GitHub Actions publisher with organization/user jiridudekusy, repository signal-cli-mcp, and workflow filename publish.yml. The workflow already requests id-token: write and upgrades npm to ≥ 11.5.1.

To cut a release:

npm version patch    # or minor / major — bumps package.json, commits, and tags vX.Y.Z
git push --follow-tags

The workflow checks out the tag, runs npm ci, builds, runs the tests, verifies the tag matches package.json, and publishes. Once published, install with npm install -g signal-cli-mcp (the signal-cli-mcp binary can then be used as the command in .mcp.json).