Slack MCP Server

A Model Context Protocol (MCP) server that posts notifications to Slack via an Incoming Webhook. AI agents call tools instead of shelling out to curl.

Features

• send_message — plain text and optional Block Kit blocks
• send_payload — pre-built payload object or multi-part array (rate-limit aware)
• send_markdown — Markdown → Block Kit conversion with Slack size limits and splitting
• STDIO and SSE transports
• Works with Claude Code, Cursor, OpenCode, and other MCP clients

Installation

git clone https://github.com/rokej/slack-mcp-server.git
cd slack-mcp-server
pip install -e ".[dev]"

Or install a release wheel:

pip install https://github.com/rokej/slack-mcp-server/releases/download/v0.1.0/slack_mcp_server-0.1.0-py3-none-any.whl

Configuration

Copy .env.example to .env (or export the variable):

export SLACK_WEBHOOK_URL="https://hooks.slack.com/services/T…/B…/…"

Create a webhook at Slack API — Your Apps → Incoming Webhooks.

Usage

# STDIO (default) — for MCP clients
slack-mcp-server

# SSE transport
slack-mcp-server --transport sse --port 8080

Claude Code / Cursor / OpenCode

{
  "mcpServers": {
    "slack-webhook": {
      "command": "slack-mcp-server",
      "env": {
        "SLACK_WEBHOOK_URL": "${SLACK_WEBHOOK_URL}"
      }
    }
  }
}

In Agent Swarm, add Slack Webhook from the workspace MCP catalog — Swarmer injects SLACK_WEBHOOK_URL into sandboxes.

Agent container images

Pin a release wheel the same way as jira-mcp-server:

ARG SLACK_MCP_VERSION=0.1.0
RUN curl -fsSL -o /tmp/slack_mcp_server-${SLACK_MCP_VERSION}-py3-none-any.whl \
      "https://github.com/rokej/slack-mcp-server/releases/download/v${SLACK_MCP_VERSION}/slack_mcp_server-${SLACK_MCP_VERSION}-py3-none-any.whl" \
    && python3 -m pip install --no-cache-dir /tmp/slack_mcp_server-*.whl \
    && rm -f /tmp/slack_mcp_server-*.whl \
    && slack-mcp-server --help | head -5

Tools

Tool	Purpose
send_message	Post plain text + optional Block Kit blocks
send_payload	Post a pre-built JSON payload (object or array)
send_markdown	Convert Markdown to Block Kit and send

Development

pip install -e ".[dev]"
make test
make lint

Releasing

1. Bump version in pyproject.toml and __version__ in slack_mcp_server/__init__.py
2. Commit, then tag and push:

   git tag v0.1.0
   git push origin v0.1.0
   

3. The Release workflow builds slack_mcp_server-X.Y.Z-py3-none-any.whl and attaches it to the GitHub Release

License

Apache License 2.0 — see LICENSE.