Slack MCP Server for Private Channels

An independently maintained Model Context Protocol (MCP) server for Slack. It supports public and private channel discovery, channel history, thread history, messages, reactions, and user profiles.

This is not the official @modelcontextprotocol/server-slack package and is not affiliated with Anthropic, Slack, or the Model Context Protocol project. It is derived from Anthropic's archived MIT-licensed Slack server; see Attribution.

Requirements

• Node.js 20 or newer

• A Slack app with a bot token (xoxb-...)

• The Slack app installed in the target workspace

• The app invited to every private channel it needs to access

Related MCP server: slack-mpm

Slack scopes

Grant only the scopes needed for the tools you intend to use:

Scopes alone do not expose private channels: invite the Slack app to each private channel first. After changing scopes, reinstall the app to the workspace.

Install

Run directly with npm:

npx -y @gustavonline/slack-mcp-server-private-channels

Or install globally:

npm install --global @gustavonline/slack-mcp-server-private-channels
slack-mcp-private-channels

MCP client configuration

{
  "mcpServers": {
    "slack-private-channels": {
      "command": "npx",
      "args": [
        "-y",
        "@gustavonline/slack-mcp-server-private-channels"
      ],
      "env": {
        "SLACK_BOT_TOKEN": "xoxb-your-bot-token",
        "SLACK_TEAM_ID": "T01234567",
        "SLACK_CHANNEL_IDS": "C01234567,G76543210"
      }
    }
  }
}

SLACK_CHANNEL_IDS is optional. When present, it is an enforced allowlist for every channel-specific tool, not merely a filter for channel listing. Leave it unset to let Slack permissions and channel membership determine access.

Never commit a real Slack token to source control. Prefer your MCP client's secret storage or an environment-injection mechanism.

Tools

• slack_list_channels — list public and private channels, with cursor pagination

• slack_get_channel_history — read messages in a channel, with cursor pagination

• slack_get_thread_replies — read a complete thread page, with cursor pagination

• slack_post_message — post a channel message

• slack_reply_to_thread — reply to a thread

• slack_add_reaction — add an emoji reaction

• slack_get_users — list workspace users, with cursor pagination

• slack_get_user_profile — read a user's detailed profile

Slack responses are returned as JSON text. Slack API failures are marked as MCP tool errors. Missing private-channel scopes include actionable guidance for groups:read or groups:history.

Environment variables

The server keeps the MCP connection available when required configuration is missing and returns a configuration error for tool calls. It does not log tokens, message text, or complete tool arguments.

Docker

Build from the repository root:

docker build -t slack-mcp-private-channels .

Run it as a stdio MCP server:

docker run --rm -i \
  -e SLACK_BOT_TOKEN \
  -e SLACK_TEAM_ID \
  -e SLACK_CHANNEL_IDS \
  slack-mcp-private-channels

The image runs as the unprivileged node user.

Development

npm ci
npm run check
npm pack --dry-run
npm publish --dry-run

Tests mock Slack's HTTP API and specifically cover private channel discovery, conversations.history, conversations.replies, scope errors, pagination, and allowlist enforcement. No real Slack credentials are required.

Release bootstrap

Publishing is intentionally separate from CI. The Publish to npm workflow runs only after a manual workflow_dispatch and targets the protected GitHub Environment npm-publish. It requests only contents: read and id-token: write, stores no npm token, verifies the package again, and publishes with npm provenance.

Before using the workflow, the package owner must:

1. Approve the exact package name and version and confirm that the version is not already present in the npm registry.

2. Establish the package under the @gustavonline scope using an owner-authorized npm first-publish/bootstrap path. If npm requires an authenticated first publication before a Trusted Publisher can be added, that one-time action must be performed explicitly by the owner; this workflow does not bootstrap ownership.

3. In npm package settings, configure a GitHub Actions Trusted Publisher for owner gustavonline, repository slack-mcp-server-private-channels, workflow filename release.yml, and environment npm-publish.

4. In GitHub repository settings, create the npm-publish Environment, limit it to the intended release branch, and add an owner as required reviewer.

5. Confirm that npm Trusted Publisher access, GitHub Environment approval, and repository push authority are all active before running the workflow.

The workflow must not be run merely to test publishing. Use npm publish --dry-run locally or in CI for payload validation. A workflow run performs a real public npm publication after the environment approval gate.

Troubleshooting private channels

If a private channel is missing or history fails:

1. Add groups:read for discovery and groups:history for channel/thread history.

2. Reinstall the Slack app after changing OAuth scopes.

3. Invite the app to the private channel.

4. If SLACK_CHANNEL_IDS is set, include that channel's ID (often starting with G).

5. Inspect the returned Slack error such as missing_scope or not_in_channel.

Security

Use the smallest practical Slack scope set and optionally configure SLACK_CHANNEL_IDS as a defense-in-depth allowlist. See SECURITY.md for private vulnerability reporting.

Attribution

This project is derived from the Slack server in the archived Model Context Protocol servers repository, originally Copyright © 2024 Anthropic, PBC and released under the MIT License. Subsequent private-channel support and maintenance are by Gustav Anderson.

The package identity, maintainer, repository, and documentation describe this fork rather than implying that it is the official upstream package. See NOTICE and LICENSE.