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signal-mcpl

An MCPL server bridging Signal via the signal-cli daemon (HTTP JSON-RPC + SSE).

Exposes Signal DMs and group chats as MCPL channels, plus signal_send and signal_react tools.

Conversation

Channel id

Tags

DM

signal:dm:<uuid>

chat:dm, chat:addressed, chat:from-human

Group

signal:group:<gid>

chat:ambient, chat:from-human

Reaction

(either)

chat:reaction, chat:ambient, chat:from-human

The chat:addressed / chat:ambient split is the useful part for a host: DMs are addressed to the agent and generally warrant waking it; group traffic is ambient and can be archived for continuity without spending inference on every message.

Requirements

  • Node >= 20

  • A running signal-cli daemon with the HTTP JSON-RPC + SSE interface enabled

Related MCP server: mcp-signal

Usage

signal-mcpl --stdio

Configuration

All configuration is via environment variables. Nothing is hardcoded.

Variable

Default

Purpose

SIGNAL_DAEMON_URL

http://127.0.0.1:8090

signal-cli daemon base URL

SIGNAL_ACCOUNT

(unset)

Your own E.164 number; used to detect reactions to your own messages

SIGNAL_SELF_UUID

(unset)

Your own account UUID, same purpose

SIGNAL_DM_USERS

(unset — open)

Comma-separated allowlist of UUIDs/numbers. Unset means no filtering.

SIGNAL_CONTACTS_FILE

(unset)

JSON file persisting the uuid/group -> display-name map

SIGNAL_ATTACH_DIR

$HOME/.local/share/signal-cli/attachments

Where signal-cli writes attachments

SIGNAL_ATTACH_MAX_BYTES

4000000

Max image size bridged as base64

SIGNAL_DEBUG_LOG

(unset — off)

Append-only JSONL debug log

Notes

  • Markdown bold/italic/strikethrough/code is converted to Signal text styles (BodyRange); headers, links and lists pass through as plain text.

  • Image attachments under SIGNAL_ATTACH_MAX_BYTES are bridged as base64 image blocks; anything else becomes a text note.

  • Author and group name are embedded in the message text, not just metadata, because hosts commonly render only the text — bare text would otherwise arrive anonymous.

  • Read receipts are sent for delivered messages.

License

Blue Oak Model License 1.0.0

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