Slack Message MCP

Tiny MCP server that exposes one tool over stdio or HTTP:

• post_slack_message posts text to the Slack channel ID provided by the caller

Environment

Set these before starting the server:

export SLACK_BOT_TOKEN="xoxb-..."

The Slack app needs chat:write and must be allowed to post in the target channel.

Optional for the HTTP server:

export PORT="3000"

The HTTP server does not perform app-level authentication. Deploy it only where the managed agent runtime or private network controls who can reach the endpoint.

Run Locally With Stdio

node server.js

Claude Code Example

claude mcp add slack-message \
  --env SLACK_BOT_TOKEN="$SLACK_BOT_TOKEN" \
  -- node /Users/agruning/Documents/MCP/slack-message-mcp/server.js

Run As Remote HTTP MCP

Claude managed agents and the Claude API MCP connector cannot connect to local stdio servers. Deploy the HTTP server behind a public HTTPS URL:

npm run start:http

The MCP endpoint is:

POST /mcp

Health check:

GET /health

Claude managed agent / Messages API shape:

{
  "mcp_servers": [
    {
      "type": "url",
      "url": "https://your-domain.example.com/mcp",
      "name": "Slack"
    }
  ],
  "tools": [
    {
      "type": "mcp_toolset",
      "mcp_server_name": "Slack",
      "default_config": {
        "enabled": false
      },
      "configs": {
        "post_slack_message": {
          "enabled": true
        }
      }
    }
  ]
}

Use the beta header required by Anthropic's MCP connector:

anthropic-beta: mcp-client-2025-11-20

Tool call arguments:

{
  "channel": "C0123456789",
  "text": "Hello from MCP"
}