MCP Server APIs

The MCP (Model Context Protocol) Server APIs provide programmatic interfaces for client libraries and applications to interact with Slack resources through a standardized protocol. For more information about MCP, see the official documentation.

Server Setup & Configuration

Before using the MCP Server APIs, you need to properly configure and deploy the server:

• 📋 Environment Configuration - Environment variables and authentication setup
• 🚀 Deployment Guide - Local, Docker, Kubernetes, and cloud deployment examples
• 🔧 CLI Reference - Complete command-line interface documentation

Deployment Modes

MCP Server supports two operational deployment modes:

1. Standalone Mode - Dedicated MCP server for client library integration
2. Integrated Mode - Combined MCP + Webhook server for complete Slack platform integration

For detailed deployment options and usage examples, see Server Modes.

Transport Options

MCP Server supports three transport mechanisms:

1. stdio - Standard input/output communication (default)
2. Server-Sent Events (SSE) - Event-based communication over HTTP
3. Streamable HTTP - HTTP-based streaming communication

For detailed transport configuration, see the CLI Reference.

Available Tools

The following MCP tools are available for Slack integration:

• ✅ Post Message - Send text messages to Slack channels
• ✅ Read Channel Messages - Retrieve message history from channels
• ✅ Read Thread Messages - Retrieve messages from specific threads
• ✅ Thread Reply - Send replies to existing threads
• ✅ Read Emojis - Get all available workspace emojis
• ✅ Add Reactions - Add emoji reactions to messages

Tool Categories

Message Operations

• slack_post_message - Send messages to channels
• slack_thread_reply - Reply to existing threads

Data Retrieval

• slack_read_channel_messages - Get channel message history
• slack_read_thread_messages - Get thread conversation history
• slack_read_emojis - Get workspace emoji information

Interactive Features

• slack_add_reactions - Add emoji reactions to messages

Authentication

All MCP tools require a valid Slack bot token set in one of the following environment variables:

• SLACK_BOT_TOKEN (recommended)
• SLACK_TOKEN (fallback)

Required OAuth Scopes

The bot must have appropriate OAuth scopes depending on the tools used:

Tool	Required Scopes
Post Message	chat:write, channels:read
Read Channel Messages	channels:history, channels:read
Read Thread Messages	channels:history, channels:read
Thread Reply	chat:write, channels:read
Read Emojis	emoji:read
Add Reactions	reactions:write, channels:read

Usage Examples

Basic Message Sending

{
  "channel": "#general",
  "text": "Hello from the MCP server!"
}

Reading Channel History

{
  "channel": "#general",
  "limit": 50
}

Adding Reactions

{
  "channel": "#general",
  "timestamp": "1234567890.123456",
  "emojis": ["thumbsup", "heart"]
}

Error Handling

MCP Server API responses follow Slack's standard format. Successful responses have "ok": true, while errors have "ok": false with error details:

{
  "ok": false,
  "error": "channel_not_found",
  "detail": "Value passed for channel was invalid."
}

Common Error Types

• Authentication Errors: invalid_auth, not_authed
• Permission Errors: not_in_channel, channel_not_found
• Rate Limiting: rate_limited
• Validation Errors: invalid_ts, msg_too_long

Rate Limiting

Slack enforces rate limits on API endpoints. The server automatically handles retries according to Slack's rate limiting headers. Consider implementing client-side rate limiting for high-frequency operations.

Best Practices

• Error Handling: Always check the ok field in responses
• Channel Format: Use channel IDs (e.g., C1234567890) for better reliability
• Token Security: Store tokens securely and never expose them in client-side code
• Rate Management: Implement appropriate delays between API calls
• Scope Minimization: Only request necessary OAuth scopes