Intro

This guide walks you through connecting the Slack MCP Server to MCP Manager so your AI clients (Claude, Cursor, and others) can search messages, send messages, manage canvases, and look up users in your Slack workspace — all through a centrally managed gateway.

The setup involves two parts: creating and configuring a Slack App with the right permissions, then connecting it to MCP Manager via OAuth pre-registration.

Part 1: Create and Configure Your Slack App

Step 1: Create a New Slack App

1. Go to api.slack.com/apps
2. Click "Create New App" → "From scratch"
3. Enter an App Name (e.g., MCP Manager) and select your Workspace
4. Click "Create App"

Step 2: Enable the MCP Protocol

1. In your app's settings, navigate to Features → Agents & AI Apps
2. Toggle "Model Context Protocol" to ON

Step 3: Configure the OAuth Redirect URI

1. Go to OAuth & Permissions

2. Under Redirect URLs, add the following URL:

   https://app.mcpmanager.ai/api/v1/mcpm/inbound/oauth/callback

3. Click "Add" then "Save URLs"

Step 4: Configure OAuth Scopes

Slack MCP uses OAuth tokens to determine what actions are available and what data can be accessed. There are two types of scopes to configure: Bot Token Scopes (for actions the app takes as itself) and User Token Scopes (for actions taken on behalf of the authenticated user).

Bot Token Scopes

Add these under Scopes → Bot Token Scopes:

User Token Scopes

Add these under Scopes → User Token Scopes. These are the scopes documented by Slack as required for the MCP server's tools:

Search:

search:read
search:read.public
search:read.private
search:read.mpim
search:read.im
search:read.files
search:read.users

Messaging:

chat:write

Channel & conversation history:

channels:history
groups:history
mpim:history
im:history

Canvases:

canvases:read
canvases:write

Users:

users:read
users:read.email

Step 5: Install the App to Your Workspace

1. Navigate to Settings → Install App
2. Click "Install to Workspace"
3. Review the permission summary and approve

If you later add or change scopes, you'll need to click "Reinstall to Workspace" for the changes to take effect.

Step 6: Collect Your App Credentials

After installation, go to Basic Information → App Credentials and copy:

• Client ID
• Client Secret

You will need both of these to configure MCP Manager in the next section. Do not share the Bot Token or User OAuth Token directly — the OAuth flow in MCP Manager handles token exchange automatically.

Part 2: Connect Slack MCP to MCP Manager

Step 1: Add the Slack MCP Server

1. Log in to MCP Manager
2. Navigate to Servers → Add Server
3. Select the "Remote" tab
4. Choose the "OAuth Pre-registration" sub-tab

Step 2: Enter Server Details

Step 3: Complete the OAuth Flow

1. Click "Connect to server"
2. You'll be redirected to Slack's OAuth consent screen
3. Review the requested permissions and click "Allow"
4. You'll be redirected back to MCP Manager

If the connection is successful, the server status will show as Connected.

Step 4: Test the Connection

Open an AI client connected to MCP Manager (such as Claude Desktop, Claude.ai, or Cursor) and try a simple query like:

Search Slack for messages in #general from the last week

If results come back, your setup is working correctly.

Troubleshooting Common Issues

"Invalid Redirect URI" During OAuth

This means the redirect URL in your Slack app doesn't match what MCP Manager is sending. To fix:

1. Go to your Slack app's OAuth & Permissions settings
2. Verify the redirect URL is exactly: https://app.mcpmanager.ai/api/v1/mcpm/inbound/oauth/callback
3. Make sure there is no trailing slash
4. Save the URL and reinstall the app to your workspace

Can Read Messages but Can't Send

This typically means the authenticated user (or bot) is not a member of the target channel. Slack requires membership to post.

• The user must join the channel in Slack before they can send messages through MCP
• Alternatively, invite the bot to the channel with /invite @YourAppName
• Confirm that chat:write is present in the appropriate scope (user or bot, depending on which token is being used)

Bot Is in Channel but Messages Fail

If the bot appears in the channel member list but still can't post:

1. Verify chat:write is in the Bot Token Scopes
2. Reinstall the app to the workspace (scope changes don't take effect until reinstall)
3. Re-invite the bot to the channel after reinstalling

Search Returns No Results

If search queries return empty results even though matching messages exist:

• Confirm that the relevant search:read.* scopes are configured on the user token
• Remember that user tokens only return results from channels and conversations the user has access to in Slack
• Newly added scopes require a reinstall of the Slack app

Security Architecture

When connected through MCP Manager, the data flow works like this:

AI Client → MCP Manager (gateway) → Slack MCP Server → Slack Workspace
                   ↕
          User's OAuth Token
          (individual Slack permissions enforced)

Each user authenticates individually via OAuth. The Slack MCP Server enforces that user's actual Slack permissions — if they can't see a channel in Slack, they can't access it through MCP. MCP Manager adds an additional layer of centralized logging, access control, and observability on top of this.

Quick Reference: Recommended Scopes

Bot Token Scopes

channels:join
channels:read
chat:write
search:read.public

User Token Scopes

# Search
search:read
search:read.public
search:read.private
search:read.mpim
search:read.im
search:read.files
search:read.users

# Messaging
chat:write

# History
channels:history
groups:history
mpim:history
im:history

# Canvases
canvases:read
canvases:write

# Users
users:read
users:read.email

Additional Resources

• Slack MCP Server Documentation — Official Slack docs covering features, rate limits, and authentication
• Connect Slack MCP to Claude — Slack's guide for direct Claude integration