# slack_post_message

Post a new message to a Slack channel

Agent View of the PolicyLayer registry record for `slack_post_message`. HTML page: https://policylayer.com/tools/slack/slack-post-message

## Facts

- Tool: `slack_post_message`
- Server: Slack (`@modelcontextprotocol/server-slack`) — https://policylayer.com/tools/slack.md
- Install: `npx -y @modelcontextprotocol/server-slack`
- Homepage: https://github.com/modelcontextprotocol/server-slack
- Risk category: Write (Medium risk)
- Registry record: grade F, identity verified
- Server rate-limited: no
- Parameters: 0
- Recommended policy verdict: Rate-limited

## Example call (MCP tools/call, JSON-RPC 2.0)

```json
{
  "jsonrpc": "2.0",
  "id": 1,
  "method": "tools/call",
  "params": {
    "name": "slack_post_message",
    "arguments": {}
  }
}
```

## Why slack_post_message is rated Medium

Posting a message creates new data in a Slack channel, which is reversible (messages can be deleted or edited by authorized users). This is a Write operation. Severity is medium because an AI agent posting unwanted, spam, or misleading messages could damage team communication and trust, but the impact is limited to message content and can be remediated.

From the tool's own definition: "Tool name 'slack_post_message' and description 'Post a new message to a Slack channel' indicate creation of new message content in Slack."

## Use case

AI agents use slack_post_message to create or update resources in Slack, usually the action step of a workflow, after the agent has gathered context. Every call changes real data in your Slack environment.

## Recommended policy (PolicyLayer)

Verdict: **Rate-limited**. Enforced by the PolicyLayer MCP gateway (https://policylayer.com/mcp-gateway) before a call reaches Slack:

```json
{
  "version": "1",
  "default": "deny",
  "tools": {
    "slack_post_message": {
      "limits": [
        {
          "counter": "slack_post_message_rate",
          "window": "minute",
          "max": 30,
          "scope": "grant"
        }
      ]
    }
  }
}
```

## Other tools on Slack (7)

- `slack_get_channel_history` — Read — https://policylayer.com/tools/slack/slack-get-channel-history.md
- `slack_get_thread_replies` — Read — https://policylayer.com/tools/slack/slack-get-thread-replies.md
- `slack_get_user_profile` — Read — https://policylayer.com/tools/slack/slack-get-user-profile.md
- `slack_get_users` — Read — https://policylayer.com/tools/slack/slack-get-users.md
- `slack_list_channels` — Read — https://policylayer.com/tools/slack/slack-list-channels.md
- `slack_add_reaction` — Write — https://policylayer.com/tools/slack/slack-add-reaction.md
- `slack_reply_to_thread` — Write — https://policylayer.com/tools/slack/slack-reply-to-thread.md

## For agents

This record is a snapshot. Live verdicts and the full registry:

- Check every server in your MCP config at once: `npx -y policylayer stack`
- Vet a server before you add it: install the mcp-precheck skill — `npx skills add https://policylayer.com` (skill text: https://policylayer.com/skill.md)
- Query the registry over MCP: endpoint `https://api.policylayer.com/mcp` — tools `check_mcp_server`, `check_mcp_stack`, `check_tool`, `search_registry`, `get_change_events`

---

Source: the PolicyLayer MCP registry — one continuously verified record per MCP server. Full record: https://policylayer.com/registry?q=slack · API: https://policylayer.com/registry/api · Policy library: https://policylayer.com/policies/slack