Connect Slack to Allin with MCP

Technical preparation

1. 1

   Create an internal Slack app dedicated to Allin at api.slack.com/apps. The official MCP accepts internal apps and apps published on the Slack Marketplace; distributed unpublished apps are not accepted.

2. 2

   In OAuth & Permissions, add the exact callback URL shown below. Enable PKCE for this dedicated app; Slack states that this setting cannot be undone without their support.

3. 3

   Add the User Token Scopes search:read.public, channels:history, channels:read, groups:read, users:read and chat:write. Messages are sent as the connected user, in conversations Slack allows them to access.

4. 4

   To search and read private channels, add search:read.private and groups:history. To create direct or group messages, add im:write or mpim:write. Update scopes in both Slack and Allin, then authorize the account again.

5. 5

   From Basic Information → App Credentials, copy the Client ID and Client Secret into Allin. Save, then authorize your Slack account. Slack does not support automatic OAuth client registration.

6. 6

   Discover tools using the administrator account, then choose Allin permissions. In personal mode, each member authorizes their own account from My connections; no administrator account is used on their behalf.

OAuth redirect URL to register

MCP server address

If the connection fails

Check approval by your Slack administrator, User Token Scopes, PKCE and the callback URL. If an IP allowlist is configured, it must allow Allin’s outbound address. An internal app can only be used in its own Slack workspace.