yt-slack-mcp

MCP server for Slack — read permalinks, threads, and channel history; reply to threads; add reactions.

Implements the Model Context Protocol specification: it runs over the stdio transport, speaks JSON-RPC 2.0, negotiates the protocol version on initialize, advertises tools capabilities, and describes each tool with a JSON Schema. Protocol version negotiation is handled by the @modelcontextprotocol/sdk Server class, which defaults to the latest supported version.

Tools

Read tools use the private Slack browser-session API (via xoxc / xoxd tokens), so they can pull private file contents — PDFs are downloaded and text-extracted (up to 50 pages / 100k chars), images are returned inline.

Related MCP server: Slack MCP Server

Setup

1. Obtain browser session tokens

• xoxc: Slack web localStorage token (from your logged-in browser session).

• xoxd: Slack cookie named d.

These may need refreshing when Slack rotates/invalidates the session.

2. Place the secrets

Save each token as a single-line file:

~/.config/opencode/secrets/slack-xoxc.txt
~/.config/opencode/secrets/slack-xoxd.txt

Or override the paths via the config file or env vars.

3. (Optional) Configure allowed write channels and paths

All configuration can live in a JSON config file at ~/.config/yt-slack-mcp/config.json (override with SLACK_MCP_CONFIG):

{
  "secretsDir": "~/.config/opencode/secrets",
  "xoxcPath": "~/.config/opencode/secrets/slack-xoxc.txt",
  "xoxdPath": "~/.config/opencode/secrets/slack-xoxd.txt",
  "allowedWriteChannels": ["C0123456789", "C0987654321"],
  "userAgent": "Mozilla/5.0"
}

By default the write tools (slack_reply_to_thread, slack_add_reaction) are locked down — no channel is writable. Every field is optional; a missing file just means defaults. Env vars always override the config file.

Configuration

Config resolution order: built-in defaults → config file → env vars.

MCP host config

opencode

{
  "mcp": {
    "slack": {
      "type": "local",
      "command": ["npx", "yt-slack-mcp"]
    }
  }
}

Claude Desktop

{
  "mcpServers": {
    "slack": {
      "command": "npx",
      "args": ["yt-slack-mcp"]
    }
  }
}

License

MIT