What it does

Lets an agent read and write Slack. Tools cover list_channels, get_channel_history, post_message, reply_to_thread, list_users, get_user_profile, and a few more. Auth is a Bot User OAuth Token issued from a Slack app you create in your workspace.

When you actually need it

Three patterns I’ve seen work:

1. Agent posts daily/weekly summaries. Agent reads a configured channel’s last 24h, summarises, posts a digest in another channel. Standalone — no human in the loop after setup.
2. Agent triages incoming threads. When a message in #support matches a pattern, the agent reads the thread context, drafts a reply, posts it in a private review channel, waits for approval, then posts publicly.
3. Agent posts decisions / changes. Used as a notification sink — when an agent does anything material (deploys, bookings, file edits), it posts a one-line “I just did X” to a #agent-log channel for human visibility.

Setup

Create a Slack app at api.slack.com/apps. Add a Bot User. Grant the minimum scopes you need (start with channels:history, chat:write). Install to workspace. Copy the Bot User OAuth Token (starts xoxb-).

"slack": {
  "command": "npx",
  "args": ["-y", "@modelcontextprotocol/server-slack"],
  "env": {
    "SLACK_BOT_TOKEN": "xoxb-…",
    "SLACK_TEAM_ID":   "T01234567"
  }
}

Then, in Slack, invite the bot user to the specific channels you want it to read/write. Don’t add it to #general or #announcements unless you genuinely need it there.

The catch

Slack’s auth model wasn’t designed for autonomous agents. Tokens are scope-based, not channel-based — chat:write writes wherever you’re invited, period. There’s no Slack-side feature that says “this bot can ONLY post in #agent-log.”

Mitigations:

• One bot per agent purpose. A summariser bot has different scopes than a triage bot. They get separate tokens.
• Curate the invite list. Treat the list of channels the bot is in as a security artifact. Audit it on the same cadence you audit IAM policies.
• Watch the workspace audit log. Anyone with admin in the workspace can see every message a bot has posted. Use it.
• Rate-limit at the prompt level. A loose prompt can trigger Slack tier 2 rate limits; if your agent is allowed to post repeatedly, add a “no more than N posts per hour” rule in the system prompt.