Slack MCP Server

A Model Context Protocol (MCP) server that enables LLMs to interact with Slack workspaces through OAuth 2.0 authentication.

Features

• 🔐 OAuth 2.0 Authentication: Secure Slack OAuth flow with automatic token management

• 🚀 FastMCP Framework: Built with the official MCP SDK's FastMCP framework

• 💾 Token Persistence: Tokens are saved locally or in DynamoDB for cloud deployments

• 📱 Slack Integration: Post messages and list channels in Slack workspaces

• 🔄 Dynamic Client Registration: Supports VSCode MCP extension and other clients

• ☁️ GitHub + App Runner: Deploy directly from GitHub with AWS App Runner

Prerequisites

• Python 3.11+

• Slack App with OAuth 2.0 configured

• uv (Python package manager)

Quick Start

1. Slack App Configuration

1. Create a new Slack App at https://api.slack.com/apps

2. Add OAuth Scopes in "OAuth & Permissions":

   • chat:write - Post messages

   • channels:read - List channels

3. Add Redirect URLs:

   • Local: http://localhost:8080/slack/callback

   • Production: https://your-domain.com/slack/callback

4. Copy the Client ID and Client Secret

2. Installation

3. Configuration

Create a .env file:

4. Run the Server

Usage

With VSCode MCP Extension

1. Install the MCP extension for VSCode

2. Connect to the server URL: http://localhost:8080/mcp/

3. The OAuth flow will start automatically when you first use a tool

With Claude Desktop

Add to your Claude Desktop configuration:

macOS: ~/Library/Application Support/Claude/claude_desktop_config.json
Windows: %APPDATA%\Claude\claude_desktop_config.json

Available Tools

1. list_channels: Get a list of Slack channels

   Returns: Dictionary mapping channel names to IDs

2. post_message: Post a message to a Slack channel

   Args: - channel_id: Channel ID (required) - text: Message text (required) Returns: Success/failure message

3. get_auth_status: Check authentication status

   Returns: Current authentication state and session info

Authentication Flow

1. When a tool is first used, the OAuth flow automatically starts

2. A browser window opens for Slack authorization

3. After authorization, the token is saved for future use

4. Subsequent requests use the cached token

Authentication

The server uses FastMCP's built-in OAuth 2.0 support with dynamic client registration. This allows compatibility with various MCP clients including VSCode's MCP extension.

Token Management

• OAuth tokens are mapped between MCP tokens and Slack tokens internally

• Tokens are persisted locally in memory (or DynamoDB in cloud)

• OAuth flow starts automatically when tools are first used

• Dynamic client registration supported for VSCode and other clients

Port Configuration

The server uses a single port:

• 8080: MCP server endpoint (includes health check and OAuth callback routes)

AWS App Runner Deployment (ECR-based)

The project uses ECR-based deployment with AWS App Runner for production:

App Runner provides:

• Deployment from ECR with pre-built Docker images

• Built-in HTTPS with automatic certificates

• Manual deployment control (auto-deploy disabled by default)

• Auto-scaling and simplified management

• Avoids Python 3.11 build issues with App Runner's source code deployment

Project Structure

Development

Testing

Debugging

Enable debug logging by checking server.log:

Troubleshooting

Port Already in Use

OAuth Errors

1. bad_redirect_uri: Ensure the redirect URL in Slack app matches exactly:

   • Must include the full path: http://localhost:8080/slack/callback

   • Port must be 8080 (MCP server port)

2. invalid_client_id: Verify SLACK_CLIENT_ID in .env

3. Token not found: Complete OAuth by authorizing in browser

Security Considerations

• OAuth tokens are mapped between MCP tokens and Slack tokens

• Tokens stored in memory locally, DynamoDB in production

• Dynamic client registration supports various MCP clients

• OAuth callbacks use HTTPS in production (App Runner)

Contributing

1. Fork the repository

2. Create a feature branch

3. Follow the guidelines in CLAUDE.md

4. Submit a pull request

License

MIT License - see LICENSE file for details

References

• MCP Documentation

• MCP Python SDK

• Slack API Documentation