Slack Notify

This MCP server lets you post messages to Slack through either webhooks or the Slack Bot API. It provides convenient modes for simple posting or full API interactions, supports channel overrides, and handles Slack-specific mention syntax and validation to ensure reliable messaging from your MCP workflows.

How to use

You set up the server in one of two modes and then send messages through your MCP client. In webhook mode you configure a Slack webhook URL and an optional default channel. In bot mode you use a bot token and a channel ID. You can override the default username and emoji for individual messages and rely on Slack’s mention syntax for targeted notifications.

How to install

Prerequisites: you need a runtime that can execute the MCP server. This setup uses Bun as the runtime. Ensure Bun is installed on your system before proceeding.

1. Install dependencies using Bun.

2. Start the MCP server using the provided runtime command blocks for either webhook or bot mode.

Configuration and usage notes

Choose a mode and configure the MCP client with one of the following server definitions. Each definition specifies how messages are sent to Slack. Use the webhook mode for simple posting via a Slack webhook, or the bot mode for full API access with a Bot User OAuth Token.

{
  "mcpServers": {
    "slack-webhook": {
      "command": "bun",
      "args": [
        "run", 
        "src/index.ts",
        "--webhook-url",
        "https://hooks.slack.com/services/YOUR/SLACK/WEBHOOK",
        "--channel",
        "#general"
      ],
      "cwd": "/path/to/slack-webhook-mcp-server"
    }
  }
}

{
  "mcpServers": {
    "slack-bot": {
      "command": "bun",
      "args": [
        "run", 
        "src/index.ts",
        "--bot-token",
        "xoxb-YOUR-BOT-TOKEN",
        "--channel",
                  "CXXXXXXXXXX",
        "--username",
        "MCP Bot"
      ],
      "cwd": "/path/to/slack-webhook-mcp-server"
    }
  }
}

Slack-specific features and tips

This server supports Slack mentions, channel overrides, and per-message customization. Use <@USERID> to mention users, <!channel> or <!here> for channel-wide alerts, and set --username or --icon_emoji to tailor each message.

In webhook mode you reference channels by name (for example, #general). In bot mode you reference channels by ID (for example, CXXXXXXXXXX). Ensure you have the appropriate permissions for the mode you choose.

Mode comparison

Webhook Mode is simple to set up and uses a Slack webhook URL with basic messaging permissions. Bot Mode offers full API access but requires OAuth setup and channel IDs.

Error handling and validation

The server performs validation on webhook URLs and bot tokens, handles network issues, maps Slack API errors to clear messages, enforces the 4000 character limit for messages, validates channel references, and checks for malformed requests to ensure reliable operation.

Development

Development scripts include starting, watching, and building the server to production readiness. Use the provided commands to run or develop the MCP locally.

Project structure

Slack MCP server layout includes a TypeScript source, types definitions, and build artifacts. You will work with the main entry in src/index.ts and type definitions in types/slack.ts.

Error handling and troubleshooting notes

If you encounter invalid URLs, token errors, network failures, Slack API responses, or message length issues, verify your configuration, re-authenticate tokens if needed, and check that the channel references (name or ID) match your workspace setup.

Notes on security and usage

Keep your Slack credentials secure. Do not expose webhook URLs or bot tokens in public configs. Use environment-based or secret management where possible and rotate credentials if exposure is suspected.

Available tools

post_slack_message

Post a message to Slack using either webhook or bot mode, with optional overrides for channel, username, and icon.