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Slack MCP

Status

Owner: TBD · Status: draft · Canonical source: flezi.app.frontend.main/src/components/mcp-servers/slack/, flezi.app.api.backend/app/integrations/slack/

Who is this for?​

Administrators enabling Slack MCP for an organization and members who want Agents to act in Slack with their own user permissions.

How it works​

The Slack connector uses Slack's hosted MCP endpoint and user-centric OAuth:

MCP endpoint: https://mcp.slack.com/mcp
Authorization: https://slack.com/oauth/v2_user/authorize
Token endpoint: https://slack.com/api/oauth.v2.user.access

The flow uses OAuth 2.0 PKCE. Flezi Galaxy stores tokens per connector + user and never substitutes a bot token for a user token.

Administrator setup​

  1. Open the Slack app and enable the Slack MCP Server capability.

  2. Add the user scopes required by the tools your organization needs.

  3. Register the exact redirect URL:

    https://<api-host>/api/v1/integrations/slack/callback

    Use the URI returned by backend connector status; <api-host> is the API host and is not necessarily the SPA origin.

  4. In Slack MCP setup, enter the Slack Client ID and Slack Client Secret. The secret is stored server-side and never returned in status responses.

  5. Ensure the Slack workspace admin approves the integration when required.

Managing app credentials requires System Admin, Org Admin, or Workspace Admin. A Client ID may be saved first, but authorization cannot start until a server-side Client Secret is available.

Connect an account​

  1. Open MCP Servers and select the Slack connector.
  2. In Account & OAuth, review the requested user scopes.
  3. Click Sign in with Slack and approve the permissions.
  4. Verify the workspace, Slack user ID, and Connected status.
  5. Run Test Connection to discover tools.

Each member authorizes separately. Disconnecting your account removes only your token for that connector.

Tools and scopes​

Tools shown in Tools Explorer depend on the endpoint and scopes Slack grants. Common groups include:

  • Searching and reading messages or threads.
  • Listing channels and conversations.
  • Sending messages to channels or threads.
  • Accessing users, files, canvases, or lists when the corresponding scope is granted.

Keep scopes minimal for organizational needs. Backend deployments may narrow the list with SLACK-OAUTH-SCOPES.

Troubleshooting​

  • Client Secret required: Add the secret in setup; Slack's code exchange needs it server-side.
  • Needs OAuth: Authorize the current account before Test Connection.
  • Bot token rejected: This connector requires a user token from the user OAuth flow, not an xoxb- bot token.
  • 403 or missing tools: Check user scopes, the Slack MCP capability, and workspace-admin approval.
  • OAuth returns without Connected: Only backend oauth_result=success confirms success; mcp_connected=1 alone is not sufficient.