MCP Slack

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.

Variable	Required	Default	Description
SLACK_USER_TOKEN	token mode	—	User OAuth token (xoxp-...) from a Slack app installed in the workspace.
SLACK_COOKIE_TOKEN	cookie mode	—	Browser session token (xoxc-...). Must be paired with SLACK_COOKIE_D.
SLACK_COOKIE_D	cookie mode	—	Value of the d cookie (xoxd-...) from the same browser session. Sent as a Cookie: header alongside SLACK_COOKIE_TOKEN.
SLACK_ADD_MESSAGE_DELAY	no	3m	How far ahead outgoing messages are scheduled, giving you a window to cancel one. Duration string: 30s, 5m, 2h, or a bare integer for seconds. Set to 0, 0s, none, or false to disable scheduling and post immediately.

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

Tool	Description
slack_auth_test	Test connection and get token owner info
slack_list_channels	List workspace channels
slack_get_channel_info	Get channel details
slack_get_channel_history	Read channel messages
slack_get_thread_replies	Read thread replies
slack_list_channel_members	List channel members
slack_search_messages	Search messages
slack_get_reactions	Get message reactions
slack_list_reactions	List user's reactions
slack_list_stars	List starred items
slack_get_user_info	Get user details
slack_list_users	List workspace members
slack_get_user_profile	Get user profile
slack_list_files	List files (metadata only)
slack_get_file_info	Get file metadata
slack_send_message	Schedule a message SLACK_ADD_MESSAGE_DELAY ahead, or post it immediately when the delay is 0 (write)
slack_cancel_scheduled_message	Cancel a scheduled message before it sends (write)

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