mcp-slack

MCP server for Slack integration, built with FastMCP. Provides tools for listing channels, reading messages, and posting to Slack.

Install

pip install -e ".[dev]"

Environment Variables

Variable	Required	Description
SLACK_BOT_TOKEN	Yes	Bot User OAuth Token (xoxb-...)
SLACK_DEFAULT_CHANNEL	No	Fallback channel for slack_post_message

Copy .env.example to .env and fill in your values.

Tools

Tool	Description
slack_list_channels	List all channels accessible by the bot
slack_read_channel(channel, limit?)	Read last N messages from a channel (default: 20, max: 100)
slack_post_message(channel, text)	Send a message to a channel

The channel parameter accepts either a channel name (without #) or a Slack channel ID.

Slack App Setup

1. Go to api.slack.com/apps and create a new app

2. Under OAuth & Permissions, add the required Bot Token Scopes for the tools you want to use:

   Tool	Required Bot Scopes
   slack_list_channels	channels:read, groups:read
   slack_read_channel	channels:history, groups:history
   slack_post_message	chat:write

   Note: Private-channel access (groups:*) and DM scopes are only needed if the bot operates outside public channels.

3. Install the app to your workspace

4. Copy the Bot User OAuth Token (xoxb-...) to SLACK_BOT_TOKEN

5. Invite the bot to channels it should access: /invite @your-bot-name

Troubleshooting: missing_scope Error

If a tool fails with a missing_scope error, it means the bot doesn't have the necessary permissions to perform that action. Check the error message to see which scope is missing, cross-reference it with the table above, and add the missing scope in your Slack App's OAuth & Permissions page. (Remember to reinstall the app to your workspace after changing scopes!)

Usage

Standalone

mcp-slack

Claude Desktop config

{
  "mcpServers": {
    "slack": {
      "command": "mcp-slack",
      "env": {
        "SLACK_BOT_TOKEN": "xoxb-your-token"
      }
    }
  }
}

Development

pip install -e ".[dev]"
ruff check src/ tests/
ruff format src/ tests/
pytest

License

MIT