mcp-slack-crunchtools

Secure MCP server for Slack workspaces. Provides Claude Code (and other MCP clients) with read access to your Slack channels, messages, users, and files, and can send a message on your behalf.

Features

• Mostly read: 15 of the 17 tools only read and publish readOnlyHint: true. The other two send a message and cancel a scheduled one; nothing edits or deletes existing content.
• Secure: 6-layer security model (input validation, token handling, client hardening, output sanitization, runtime protection, supply chain security).
• User OAuth Token: Uses xoxp- tokens for user-scoped access to your workspace.
• No SDK dependency: Uses httpx directly for minimal, auditable HTTP calls.

Quick Start

Using uvx (Recommended)

claude mcp add mcp-slack-crunchtools \
    --env SLACK_USER_TOKEN=xoxp-your-token \
    -- uvx mcp-slack-crunchtools

Using Container

claude mcp add mcp-slack-crunchtools \
    --env SLACK_USER_TOKEN=xoxp-your-token \
    -- podman run -i --rm -e SLACK_USER_TOKEN quay.io/crunchtools/mcp-slack

Local Development

claude mcp add mcp-slack-crunchtools \
    --env SLACK_USER_TOKEN=xoxp-your-token \
    -- uv run mcp-slack-crunchtools

Setup

See CLAUDE.md for detailed instructions on creating a Slack app and obtaining a User OAuth Token.

Configuration

Authentication uses one of two mutually exclusive modes. The server picks cookie mode when both cookie variables are set, and token mode otherwise.

Which auth mode to use

Cookie mode is the working path for this deployment. Token mode requires a Slack app to be created and approved in the workspace; where that approval is not available, cookie mode is the only way to authenticate at all.

Cookie mode borrows an existing browser session rather than holding a credential issued to an application. That has consequences worth stating plainly:

• Both values are live session credentials. Anything holding them can act as you in Slack, with your full access. Treat them exactly as you would your password.
• They expire when the browser session does, so cookie mode needs periodic re-extraction. A sudden wave of auth failures usually means the session rotated, not that the server broke.
• Slack does not issue these for programmatic use and can invalidate them at any time. Cookie mode is a workaround for the absence of an approved app, not a supported integration path.

Prefer SLACK_USER_TOKEN whenever a Slack app can actually be installed.

Tools

The two write tools need the chat:write scope in token mode.

Security

See SECURITY.md for the full security design document.

License

AGPL-3.0-or-later