Slack Webhook MCP Server

A Model Context Protocol (MCP) server that enables sending messages to Slack through webhooks. This server provides a single tool send_message for sending formatted messages to Slack channels.

Features

• Send messages to Slack via webhook URLs
• Support for channel override, custom usernames, and icons
• Markdown formatting support
• Comprehensive error handling
• Docker support with multi-stage builds

Prerequisites

• Go 1.23 or later
• A Slack webhook URL (see Slack's documentation for setup)
• Docker (optional, for containerized deployment)

Installation

From Source

git clone <repository-url>
cd mcp-slack-webhook
go mod download
go build -o mcp-slack-webhook .

Using Docker

docker build -t mcp-slack-webhook .
docker run -e SLACK_WEBHOOK_URL="https://hooks.slack.com/services/YOUR/WEBHOOK/URL" mcp-slack-webhook

Usage

Running the Server

First, set the required environment variable:

export SLACK_WEBHOOK_URL="https://hooks.slack.com/services/YOUR/WEBHOOK/URL"

Then run the server:

./mcp-slack-webhook

The server will start and listen for MCP protocol messages on stdin/stdout.

Tool: send_message

The server provides a single tool called send_message with the following parameters:

Required Parameters

• text (string): The message text to send

Required Environment Variable

• SLACK_WEBHOOK_URL: The Slack webhook URL to send messages to

Optional Parameters

• channel (string): The channel to send the message to (overrides webhook default)
• username (string): Username to display as the sender
• icon_emoji (string): Emoji to use as the icon (e.g., :robot_face:)
• icon_url (string): URL to an image to use as the icon
• markdown (boolean): Whether to enable markdown formatting (default: true)

Example Tool Call

First, set the environment variable:

export SLACK_WEBHOOK_URL="https://hooks.slack.com/services/YOUR/WEBHOOK/URL"

Then call the tool:

{
  "jsonrpc": "2.0",
  "id": "1",
  "method": "tools/call",
  "params": {
    "name": "send_message",
    "arguments": {
      "text": "Hello from MCP! This is a *test* message.",
      "channel": "#general",
      "username": "MCP Bot",
      "icon_emoji": ":robot_face:",
      "markdown": true
    }
  }
}

Configuration

Slack Webhook Setup

1. Go to Slack API: Incoming Webhooks
2. Create a new webhook for your workspace
3. Copy the webhook URL for use with this server

Environment Variables

Required

• SLACK_WEBHOOK_URL: The Slack webhook URL for sending messages

Optional

You may also want to configure:

• Logging levels
• Authentication (not implemented in this basic version)

Docker Deployment

The included Dockerfile uses a multi-stage build for optimal image size:

# Build the image
docker build -t mcp-slack-webhook .

# Run the container
docker run -i -e SLACK_WEBHOOK_URL="https://hooks.slack.com/services/YOUR/WEBHOOK/URL" mcp-slack-webhook

For production use, you might want to:

# Run with environment file
docker run -i --env-file .env mcp-slack-webhook

# Or run with secrets management
docker run -i -e SLACK_WEBHOOK_URL="$(cat /path/to/webhook_url_secret)" mcp-slack-webhook

Development

Project Structure

mcp-slack-webhook/
├── main.go           # Main application code
├── go.mod            # Go module dependencies
├── go.sum            # Go dependency checksums
├── Dockerfile        # Multi-stage Docker build
└── README.md         # This file

Dependencies

• github.com/mark3labs/mcp-go v0.32.0 - MCP protocol implementation

Building

# Regular build
go build -o mcp-slack-webhook .

# Cross-compile for Linux
GOOS=linux GOARCH=amd64 go build -o mcp-slack-webhook-linux .

Testing

# Run tests (when available)
go test ./...

# Test Docker build
docker build -t mcp-slack-webhook-test .

Slack Message Format

Messages sent to Slack follow the webhook format:

{
  "text": "Your message text",
  "channel": "#channel-name",
  "username": "Bot Name",
  "icon_emoji": ":robot_face:",
  "icon_url": "https://example.com/icon.png",
  "mrkdwn": true
}

Error Handling

The server handles various error conditions:

• Invalid webhook URLs
• Missing required parameters
• Slack API errors
• Network connectivity issues

All errors are returned as MCP tool result errors with descriptive messages.

Security Considerations

• Webhook URLs are securely stored as environment variables and not exposed in tool calls
• Webhook URLs should never be logged or exposed in debug output
• Consider implementing authentication for production use
• Validate input parameters to prevent injection attacks
• Use HTTPS webhook URLs only
• In production, use secure secret management systems instead of plain environment variables

License

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Contributing

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