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andygruening

Slack Message MCP

by andygruening
OverviewSchemaRelated ServersScoreDiscussions
JavaScript
Hybrid

Slack Message MCP

Tiny MCP server that exposes one tool over stdio or HTTP:

  • post_slack_message posts text to the Slack channel ID provided by the caller

Environment

Set these before starting the server:

export SLACK_BOT_TOKEN="xoxb-..."

The Slack app needs chat:write and must be allowed to post in the target channel.

Optional for the HTTP server:

export PORT="3000"

The HTTP server does not perform app-level authentication. Deploy it only where the managed agent runtime or private network controls who can reach the endpoint.

Related MCP server: Slack

Run Locally With Stdio

node server.js

Claude Code Example

claude mcp add slack-message \
  --env SLACK_BOT_TOKEN="$SLACK_BOT_TOKEN" \
  -- node /Users/agruning/Documents/MCP/slack-message-mcp/server.js

Run As Remote HTTP MCP

Claude managed agents and the Claude API MCP connector cannot connect to local stdio servers. Deploy the HTTP server behind a public HTTPS URL:

npm run start:http

The MCP endpoint is:

POST /mcp

Health check:

GET /health

Claude managed agent / Messages API shape:

{
  "mcp_servers": [
    {
      "type": "url",
      "url": "https://your-domain.example.com/mcp",
      "name": "Slack"
    }
  ],
  "tools": [
    {
      "type": "mcp_toolset",
      "mcp_server_name": "Slack",
      "default_config": {
        "enabled": false
      },
      "configs": {
        "post_slack_message": {
          "enabled": true
        }
      }
    }
  ]
}

Use the beta header required by Anthropic's MCP connector:

anthropic-beta: mcp-client-2025-11-20

Tool call arguments:

{
  "channel": "C0123456789",
  "text": "Hello from MCP"
}

Available Tools

1 tool
post_slack_messageA

Post a message to the Slack channel configured by SLACK_CHANNEL_ID.

ParametersJSON Schema
NameRequiredDescriptionDefault
textYesMessage text to post to Slack.

TDQS

A3.8/5.0
Behavior2/5

Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

No annotations are provided, so the description carries the full burden of behavioral disclosure. It only states the action (posting) but does not mention any side effects, permissions required, rate limits, or error handling. This is insufficient for a mutation tool.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Conciseness5/5

Is the description appropriately sized, front-loaded, and free of redundancy?

The description is a single, concise sentence with no extraneous information. It is well-structured and efficient.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Completeness4/5

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

For a simple tool with one parameter and no output schema, the description is adequate. It explains the action and target. However, it could be improved by mentioning what happens on success or failure.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Parameters4/5

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

The schema covers the single parameter (text) at 100%. The description adds value by clarifying that the message is posted to a specific channel configured via environment variable, which aids understanding of the parameter's effect beyond the schema.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Purpose5/5

Does the description clearly state what the tool does and how it differs from similar tools?

The description clearly states the tool's purpose: to post a message to a specific Slack channel identified by an environment variable. The verb 'post' and resource 'message to Slack channel' are specific and unambiguous.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Usage Guidelines3/5

Does the description explain when to use this tool, when not to, or what alternatives exist?

No sibling tools exist, so differentiation is not needed. However, the description does not provide any usage context, such as prerequisites (e.g., ensuring SLACK_CHANNEL_ID is set) or when to avoid using this tool. Some guidance would be helpful.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.

Install Server
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TDQS

A3.6/5.0
Disambiguation5/5

Only one tool exists, so there is no possibility of ambiguity or overlap with other tools.

Naming Consistency5/5

With a single tool, naming consistency is inherent; the tool name 'post_slack_message' is clear and follows a standard verb_noun pattern.

Tool Count2/5

Having only one tool for a communication platform like Slack feels insufficient; users would typically expect additional tools for reading, editing, or deleting messages.

Completeness1/5

The server is severely incomplete; it only supports posting messages to a single configured channel, lacking any retrieval, modification, or multi-channel capabilities.

Maintenance

ActivitySlowing
ResponsivenessSyncing

Resources

Unclaimed servers have limited discoverability.

Looking for Admin?

If you are the server author, to access and configure the admin panel.

Related MCP Connectors

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  • Slack

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  • mcp-notify

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