Slack

Slack is the hardest of the common services to set up. Read this whole page before promising the user anything — both available paths have a real prerequisite, and neither works from a stock install with no preparation.

Path A — the built-in Slack OAuth flow (source_slack_oauth_trigger)

Blocked unless Vorno was launched with SLACK_OAUTH_CLIENT_ID and SLACK_OAUTH_CLIENT_SECRET set. There is no per-source config field for these — unlike Google, where the user can put their own client ID in config.json. Without the environment variables the trigger returns “Slack OAuth not configured”.

Check before offering this path. If the variables are absent, say so plainly rather than starting a flow that cannot finish.

Why it works this way: Slack requires an HTTPS redirect URI and rejects http://localhost, so this flow cannot use the local callback server the way Google and Microsoft do. It routes through a hosted HTTPS relay that bounces back to the local port. That relay is upstream-hosted infrastructure, which is a second reason to prefer Path B where possible.

Built-in scope sets, if you do use this path (slackService in the source config):

Set	Scopes
messaging	chat:write
channels	channels:read, channels:history, groups:read, groups:history
users	users:read, users:read.email
files	files:read, files:write
full	all of the above plus reactions:read, reactions:write, im:read, im:history, im:write, mpim:read, mpim:history, search:read

full is the default when no service is named. Do not accept the default silently — it grants DM history and workspace search. Name the set that matches what the user asked for.

Path B — Slack’s official remote MCP server

Slack shipped an official MCP server, generally available since 17 February 2026:

• URL: https://mcp.slack.com/mcp
• Transport: JSON-RPC 2.0 over Streamable HTTP
• Auth: user-token OAuth. Authorization endpoint https://slack.com/oauth/v2_user/authorize, token exchange https://slack.com/api/oauth.v2.user.access.

{
  "type": "mcp",
  "name": "Slack",
  "slug": "slack",
  "provider": "slack",
  "icon": "https://a.slack-edge.com/80588/marketing/img/meta/favicon-32.png",
  "tagline": "Workspace search, channels, and messages",
  "mcp": {
    "url": "https://mcp.slack.com/mcp",
    "authType": "oauth"
  }
}

The real prerequisite: Slack requires a registered Slack app with a fixed app ID, and only directory-published apps or internal apps may use MCP. Workspace admins approve and manage MCP client connections, and see which MCP server domains each app requests. So this is not a “click approve in the browser” flow the way Linear is — an admin has to have allowed it.

Practical consequence: verify with the user whether their workspace admin has approved an MCP client before building the source. If not, that is an organizational step, not something the agent can do. Say so and offer the in-app browser as an immediate fallback for one-off tasks.

Known client-side snag: some MCP clients send no scope parameter, which mcp.slack.com rejects. If authorization fails with a scope error, that is the cause.

Scopes (Path B), per tool

These are user-token scopes. Request the row you need, not the table.

Tool	Scopes
Search messages / channels	search:read.public, search:read.private, search:read.mpim, search:read.im
Search files	search:read.files
Read files	files:read
Search emoji	emoji:read
Search users	search:read.users
Send message	chat:write
Read channel / thread	channels:history, groups:history, mpim:history, im:history
Create conversation	channels:write (public), groups:write (private), im:write (DM), mpim:write (group DM)
Add reactions	reactions:write
Canvas read / write	canvases:read, canvases:write
User profile / email	users:read, users:read.email
List channel members	channels:read, groups:read, mpim:read

Slack derives the available tool set from the scopes granted at install, so a read-only grant produces a read-only tool list — a good default for a first rollout.

Public channels only is a real, narrower option. search:read.public + channels:history + channels:read covers “find things in our team channels” without touching DMs or private groups. Offer it before anything with im: or groups: in it.

Gotchas

• A bot token (xoxb) cannot search messages. Message search requires a user token (xoxp) with the search:read.* scopes. This is the most common first-time surprise.
• Canvases require a paid Slack plan. The MCP server itself is free; capability follows the workspace’s plan.
• The agent acts as the authorizing user and can read exactly what that user can read — no more, and no less. Say this out loud when a user asks whether it can see private channels.

When to skip the source entirely

If the user wants one export, one message, or one search and Slack auth is not already working, use the in-app browser. Slack setup has more moving parts than almost any other service here and it is often not worth it for a one-off.

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Verified 2026-08-17 against Slack’s developer docs (docs.slack.dev/ai/slack-mcp-server/) and against Vorno’s own packages/shared/src/auth/slack-oauth.ts for the built-in flow’s requirements.