Slack MCP Server — Hosted for Any AI Agent

mcp-slack — Slack MCP Server

Post messages, search conversations, and manage users in your Slack workspace.

Slack is the real-time communication hub for modern teams. This MCP server gives your AI agents the ability to post messages to any channel, read message history, search across conversations, look up user profiles, and add emoji reactions — making Slack a natural output channel for automated workflows and AI-driven notifications.

Live endpoint: https://mcp.aerostack.dev/s/aerostack/mcp-slack

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What You Can Do

• Post notifications, alerts, and summaries directly to Slack channels from any agent workflow — deploy notifications, error alerts, daily digests, and more
• Search message history to retrieve context from past conversations before an agent responds or takes action
• Look up user profiles to resolve names to user IDs or find contact details for routing
• Add emoji reactions to messages programmatically as a lightweight acknowledgment or status signal

Setup (Important — read before using)

Step 1: Create a Slack App

1. Go to api.slack.com/apps → Create New App → From scratch
2. Name it (e.g., "Aerostack Bot") and select your workspace

Step 2: Add Bot Token Scopes

Go to OAuth & Permissions → scroll to Bot Token Scopes → add these scopes:

Scope	Required For	Tools
chat:write	Required — Send messages	post_message
channels:read	Required — List channels	list_channels
channels:history	Read channel messages	get_channel_history
groups:read	List private channels	list_channels (private)
search:read	Search messages	search_messages
users:read	Look up users	get_user_info, list_users
reactions:write	Add emoji reactions	add_reaction

At minimum, add chat:write and channels:read. Add others based on which tools you need.

Step 3: Install to Workspace

Click Install to Workspace → Authorize → Copy the Bot User OAuth Token (xoxb-...).

Step 4: Invite Bot to Channels

This step is required! The bot can only post to channels it has been invited to.

In each Slack channel where you want the bot to operate:

/invite @YourBotName

Or: Click channel name → Integrations → Add apps → select your bot.

If you skip this step, you'll get a not_in_channel error when trying to post messages.

Step 5: Add to Aerostack Workspace

1. Go to your Aerostack workspace → Add Server → search "Slack"
2. Paste your SLACK_BOT_TOKEN (xoxb-...) when prompted
3. Click Test to verify the connection

Available Tools

Tool	Description	Required Scopes
list_channels	List public/private channels in the workspace	channels:read, groups:read
post_message	Post a message to a channel or thread	chat:write
get_channel_history	Get recent messages from a channel	channels:history
search_messages	Search messages across the workspace	search:read
get_user_info	Get profile info for a specific user	users:read
list_users	List all users in the workspace	users:read
add_reaction	Add an emoji reaction to a message	reactions:write

Configuration

Variable	Required	Description
SLACK_BOT_TOKEN	Yes	Slack Bot User OAuth Token (starts with xoxb-)

Troubleshooting

Error	Cause	Fix
missing_scope	Bot token doesn't have the required scope	Add the scope in Slack API dashboard → OAuth & Permissions → Reinstall the app → update token in Aerostack
not_in_channel	Bot hasn't been invited to the channel	Type /invite @YourBotName in the channel
channel_not_found	Wrong channel name or ID	Use channel ID (e.g., C6GK6DHPY) instead of #name
invalid_auth	Token is expired or wrong	Re-copy the token from Slack API dashboard

Example Prompts

"Post a message to #engineering saying the database migration completed successfully"
"Search Slack for any messages about the payment gateway outage from last week"
"List all users in the workspace and find the user ID for sarah@company.com"

Direct API Call

curl -X POST https://mcp.aerostack.dev/s/aerostack/mcp-slack \
  -H 'Content-Type: application/json' \
  -H 'X-Mcp-Secret-SLACK-BOT-TOKEN: xoxb-your-bot-token' \
  -d '{"jsonrpc":"2.0","id":1,"method":"tools/call","params":{"name":"post_message","arguments":{"channel":"#general","text":"Hello from Aerostack!"}}}'

License

MIT