yt-slack-mcp

A host-agnostic Model Context Protocol server for Slack. It communicates over stdio and can be used with any MCP client that launches local servers.

Features

• Read Slack channel history and thread replies.
• Read message permalinks from channels, DMs, and group DMs.
• Return image attachments inline, extract text from PDFs, and return text/* attachment contents inline.
• Retrieve private attachment contents through the authenticated Slack browser session.
• Reply to a thread, add a reaction, or upload local files only in explicitly allowed channel IDs.

Attachment limits: images and text files are limited to 10 MB; text attachments are truncated at 100,000 characters. PDFs are limited to 20 MB, 50 pages, and 100,000 extracted characters.

Tools

| Tool | Description | |------|-------------| | slack_read_permalink | Read a message or thread from a channel, DM, or group-DM permalink, including supported attachments. | | slack_get_replies | Read replies for a thread by channel ID and timestamp. | | slack_get_history | Read recent channel history. | | slack_reply_to_thread | Reply to a thread; restricted to allowed channels. | | slack_add_reaction | Add a reaction; restricted to allowed channels. | | slack_upload_files | Upload up to 10 local files to a channel or thread, with an optional initial comment; returns file and message permalinks; restricted to allowed channels. |

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. Store the secrets

Save each token as a single-line file:

~/.config/yt-slack-mcp/secrets/slack-xoxc.txt
~/.config/yt-slack-mcp/secrets/slack-xoxd.txt

The server reads these paths by default. Override them with the config file or environment variables if your MCP host manages secrets elsewhere.

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

By default the write tools (slack_reply_to_thread, slack_add_reaction) and slack_upload_files are locked down — no channel is writable. Each upload is limited to 10 MB. 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.

| Config file key | Env var | Default | Description | |-----------------|---------|---------|-------------| | secretsDir | SLACK_MCP_SECRETS_DIR | ~/.config/yt-slack-mcp/secrets | Directory holding the token files | | xoxcPath | SLACK_MCP_XOXC_PATH | $SECRETS_DIR/slack-xoxc.txt | Path to the xoxc token | | xoxdPath | SLACK_MCP_XOXD_PATH | $SECRETS_DIR/slack-xoxd.txt | Path to the xoxd token | | allowedWriteChannels | SLACK_MCP_ALLOWED_WRITE_CHANNELS | (none) | Channel IDs allowed for write tools (comma-separated in env) | | userAgent | SLACK_MCP_USER_AGENT | Mozilla/5.0 | HTTP User-Agent header | | (config file path) | SLACK_MCP_CONFIG | ~/.config/yt-slack-mcp/config.json | Path to the JSON config file |

MCP host configuration

Configure your MCP host to run yt-slack-mcp over stdio. The host-specific configuration varies, but the command is:

npx yt-slack-mcp

For example, Claude Desktop uses:

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

License

MIT