Slack Webhook

A Model Context Protocol (MCP) server for posting messages to Slack via webhooks or bot tokens.

- Two modes of operation: Webhooks or Bot API
- Post messages to Slack channels
- Support for channel overrides
- Configurable bot username and emoji
- Slack-specific mention support (<!channel>,<!here>,<@USERID>)
- Comprehensive error handling and validation

- Go toSlack API Apps
- Create a new app or select an existing one
- Navigate to "Incoming Webhooks"
- Enable incoming webhooks
- Add a new webhook to your workspace
- Copy the webhook URL (format:https://hooks.slack.com/services/T.../B.../...)

{ "mcpServers": { "slack-webhook": { "command": "bun", "args": [ "run", "src/index.ts", "--webhook-url", "https://hooks.slack.com/services/YOUR/SLACK/WEBHOOK", "--channel", "#general" ], "cwd": "/path/to/slack-webhook-mcp-server" } } }

- Go toSlack API Apps
- Create a new app or select an existing one
- Go to "OAuth & Permissions"
- Add bot token scopes:chat:write,chat:write.public
- Install app to workspace
- Copy the "Bot User OAuth Token" (starts withxoxb-)

{ "mcpServers": { "slack-bot": { "command": "bun", "args": [ "run", "src/index.ts", "--bot-token", "xoxb-YOUR-BOT-TOKEN", "--channel", "CXXXXXXXXXX", "--username", "MCP Bot" ], "cwd": "/path/to/slack-webhook-mcp-server" } } }

- --webhook-url <url>- Slack webhook URL (required)
- --channel <channel>- Default channel name (optional, e.g., "#general")

- --bot-token <token>- Slack bot token (required, starts withxoxb-)
- --channel <channel>- Default channel ID (required, e.g., "CXXXXXXXXXX")

- --username <username>- Default bot username (optional)
- --icon-emoji <emoji>- Default bot emoji (optional, e.g., ":robot_face:")
- --help- Show help message

bun run src/index.ts \ --webhook-url "https://hooks.slack.com/services/T00000000/B00000000/XXXXXXXXXXXXXXXXXXXXXXXX" \ --channel "#general" \ --username "Assistant"

bun run src/index.ts \ --bot-token "xoxb-YOUR-BOT-TOKEN" \ --channel "CXXXXXXXXXX" \ --username "Assistant"

Post a message to your configured Slack integration.

- message(required): The message content to send (max 4000 characters)
- channel(optional): Channel to post to (overrides default)

- Webhook mode: Channel name (e.g., "#random")
- Bot mode: Channel ID (e.g., "CXXXXXXXXXX")

Please post "Hello from MCP!" to the general channel

- User mention:<@U1234567890>
- Channel notification:<!channel>
- Here notification:<!here>

- Webhook mode: Use#channel-nameformat
- Bot mode: Use channel IDs likeCXXXXXXXXXX

- bun run start- Start the server
- bun run dev- Start with file watching
- bun run build- Build for production

slack-webhook-mcp-server/ ├── package.json # Dependencies and scripts ├── src/ │ └── index.ts # Main server implementation ├── types/ │ └── slack.ts # TypeScript types and schemas └── README.md # This file

The server includes comprehensive error handling for:

- Invalid webhook URLs and bot tokens
- Network connectivity issues
- Slack API errors (different handling for webhook vs bot)
- Message length validation (4000 char limit)
- Channel ID validation (bot mode)
- Malformed requests

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