slack-fast-mcp

A Slack MCP server built with FastMCP that gives AI assistants tools to read, search, and interact with Slack workspaces. Python 3.13+, fully async.

Features

Read tools (always available):

• conversations_history — Get messages from a channel or DM

• conversations_replies — Get a thread of messages

• conversations_search_messages — Search messages with filters (requires user token)

• channels_list — List channels

• users_search — Search users by name, email, or display name

• attachment_get_data — Download file attachments (up to 5MB)

Write tools (disabled by default, opt-in via env vars):

• conversations_add_message — Post a message to a channel or DM

• reactions_add / reactions_remove — Add or remove emoji reactions

Resources:

• slack://{workspace}/users — User directory

• slack://{workspace}/channels — Channel directory

Related MCP server: Slack MCP Server

Authentication

Three authentication methods are supported, in priority order:

1. User token (recommended)

Requires a Slack app with user token scopes. Supports all features including message search.

export SLACK_MCP_XOXP_TOKEN=xoxp-...

2. Bot token

Requires a Slack app with bot token scopes. Cannot search messages.

export SLACK_MCP_XOXB_TOKEN=xoxb-...

3. Browser cookie auth (no app install required)

Uses your existing Slack browser session. No Slack app installation or workspace admin approval needed — useful when your workspace restricts app installs.

export SLACK_MCP_XOXC_TOKEN=xoxc-...
export SLACK_MCP_XOXD_TOKEN=xoxd-...

Both values must be set together. To extract them:

1. Open your Slack workspace in a browser and log in

2. Open DevTools (F12)

3. xoxc token — paste this in the browser console:

   JSON.parse(localStorage.localConfig_v2).teams[document.location.pathname.match(/^\/client\/([A-Z0-9]+)/)[1]].token

4. xoxd token — go to Application > Cookies > https://app.slack.com, copy the value of the cookie named d

Caveats:

• Tokens are tied to your browser session and will expire when you log out or Slack rotates sessions. You'll need to re-extract them periodically.

• All API calls appear as your user account, not a bot.

• This uses standard Slack API endpoints with session cookies — it does not use undocumented internal APIs.

Installation

uv sync --all-extras

Usage

export SLACK_MCP_XOXP_TOKEN=xoxp-...  # or xoxb/xoxc+xoxd (see above)
uv run python -m slack_fast_mcp

Claude Desktop / Claude Code

Add to your MCP config:

{
  "mcpServers": {
    "slack": {
      "command": "uv",
      "args": ["run", "--project", "/path/to/slack-fast-mcp", "python", "-m", "slack_fast_mcp"],
      "env": {
        "SLACK_MCP_XOXP_TOKEN": "xoxp-..."
      }
    }
  }
}

Configuration

All configuration is via environment variables.

Token (required — one of)

Write tool gating (optional)

Write tools are disabled by default. Enable them with these env vars. Each accepts:

• "true" or "1" — enable for all channels

• Comma-separated channel IDs — allowlist (e.g. C001,C002)

• !-prefixed channel IDs — blocklist (e.g. !C003,!C004)

Other options

Development

make build       # Install dependencies
make test        # Run unit tests
make format      # Format code (ruff)
make lint        # Lint code (ruff)