Slack Automation via Rube MCP

Automate Slack workspace operations including messaging, search, channel management, and reaction workflows through Composio's Slack toolkit.

Toolkit docs: composio.dev/toolkits/slack

Prerequisites

• Rube MCP must be connected (RUBE_SEARCH_TOOLS available)
• Active Slack connection via RUBE_MANAGE_CONNECTIONS with toolkit slack
• Always call RUBE_SEARCH_TOOLS first to get current tool schemas

Setup

Get Rube MCP: Add https://rube.app/mcp as an MCP server in your client configuration. No API keys needed — just add the endpoint and it works.

1. Verify Rube MCP is available by confirming RUBE_SEARCH_TOOLS responds
2. Call RUBE_MANAGE_CONNECTIONS with toolkit slack
3. If connection is not ACTIVE, follow the returned auth link to complete Slack OAuth
4. Confirm connection status shows ACTIVE before running any workflows

Core Workflows

1. Send Messages to Channels

When to use: User wants to post a message to a Slack channel or DM

Tool sequence:

1. SLACK_FIND_CHANNELS - Resolve channel name to channel ID Prerequisite]
2. SLACK_LIST_ALL_CHANNELS - Fallback if FIND_CHANNELS returns empty/ambiguous results Fallback]
3. SLACK_FIND_USERS - Resolve user for DMs or @mentions Optional]
4. SLACK_OPEN_DM - Open/reuse a DM channel if messaging a user directly Optional]
5. SLACK_SEND_MESSAGE - Post the message with resolved channel ID Required]
6. SLACK_UPDATES_A_SLACK_MESSAGE - Edit the posted message if corrections needed Optional]

Key parameters:

• channel: Channel ID or name (without '#' prefix)
• markdown_text: Preferred field for formatted messages (supports headers, bold, italic, code blocks)
• text: Raw text fallback (deprecated in favor of markdown_text)
• thread_ts: Timestamp of parent message to reply in a thread
• blocks: Block Kit layout blocks (deprecated, use markdown_text)

Pitfalls:

• SLACK_FIND_CHANNELS requires query param; missing it errors with "Invalid request data provided"
• SLACK_SEND_MESSAGE requires valid channel plus one of markdown_text/text/blocks/attachments
• Invalid block payloads return error=invalid_blocks (max 50 blocks)
• Replies become top-level posts if thread_ts is omitted
• Persist response.data.channel and response.data.message.ts from SEND_MESSAGE for edit/thread operations

2. Search Messages and Conversations

When to use: User wants to find specific messages across the workspace

Tool sequence:

1. SLACK_FIND_CHANNELS - Resolve channel for scoped search with in:#channel Optional]
2. SLACK_FIND_USERS - Resolve user for author filter with from:@user Optional]
3. SLACK_SEARCH_MESSAGES - Run keyword search across accessible conversations Required]
4. SLACK_FETCH_MESSAGE_THREAD_FROM_A_CONVERSATION - Expand threads for relevant hits Required]

Key parameters:

• query: Search string supporting modifiers (in:#channel, from:@user, before:YYYY-MM-DD, after:YYYY-MM-DD, has:link, has:file)
• count: Results per page (max 100), or total with auto_paginate=true
• sort: 'score' (relevance) or 'timestamp' (chronological)
• sort_dir: 'asc' or 'desc'

Pitfalls:

• Validation fails if query is missing/empty
• ok=true can still mean no hits (response.data.messages.total=0)
• Matches are under response.data.messages.matches (sometimes also response.data_preview.messages.matches)
• match.text may be empty/truncated; key info can appear in matches[].attachments[]
• Thread expansion via FETCH_MESSAGE_THREAD can truncate when response.data.has_more=true; paginate via response_metadata.next_cursor

3. Manage Channels and Users

When to use: User wants to list channels, users, or workspace info

Tool sequence:

1. SLACK_FETCH_TEAM_INFO - Validate connectivity and get workspace identity Required]
2. SLACK_LIST_ALL_CHANNELS - Enumerate public channels Required]
3. SLACK_LIST_CONVERSATIONS - Include private channels and DMs Optional]
4. SLACK_LIST_ALL_USERS - List workspace members Required]
5. SLACK_RETRIEVE_CONVERSATION_INFORMATION - Get detailed channel metadata Optional]
6. SLACK_LIST_USER_GROUPS_FOR_TEAM_WITH_OPTIONS - List user groups Optional]

Key parameters:

• cursor: Pagination cursor from response_metadata.next_cursor
• limit: Results per page (default varies; set explicitly for large workspaces)
• types: Channel types filter ('public_channel', 'private_channel', 'im', 'mpim')

Pitfalls:

• Workspace metadata is nested under response.data.team, not top-level
• SLACK_LIST_ALL_CHANNELS returns public channels only; use SLACK_LIST_CONVERSATIONS for private/IM coverage
• SLACK_LIST_ALL_USERS can hit HTTP 429 rate limits; honor Retry-After header
• Always paginate via response_metadata.next_cursor until empty; de-duplicate by id

4. React to and Thread Messages

When to use: User wants to add reactions or manage threaded conversations

Tool sequence:

1. SLACK_SEARCH_MESSAGES or SLACK_FETCH_CONVERSATION_HISTORY - Find the target message Prerequisite]
2. SLACK_ADD_REACTION_TO_AN_ITEM - Add an emoji reaction Required]
3. SLACK_FETCH_ITEM_REACTIONS - List reactions on a message Optional]
4. SLACK_REMOVE_REACTION_FROM_ITEM - Remove a reaction Optional]
5. SLACK_SEND_MESSAGE - Reply in thread using thread_ts Optional]
6. SLACK_FETCH_MESSAGE_THREAD_FROM_A_CONVERSATION - Read full thread Optional]

Key parameters:

• channel: Channel ID where the message lives
• timestamp / ts: Message timestamp (unique identifier like '1234567890.123456')
• name: Emoji name without colons (e.g., 'thumbsup', 'wave::skin-tone-3')
• thread_ts: Parent message timestamp for threaded replies

Pitfalls:

• Reactions require exact channel ID + message timestamp pair
• Emoji names use Slack's naming convention without colons
• SLACK_FETCH_CONVERSATION_HISTORY only returns main channel timeline, NOT threaded replies
• Use SLACK_FETCH_MESSAGE_THREAD_FROM_A_CONVERSATION with parent's thread_ts to get thread replies

5. Schedule Messages

When to use: User wants to schedule a message for future delivery

Tool sequence:

1. SLACK_FIND_CHANNELS - Resolve channel ID Prerequisite]
2. SLACK_SCHEDULE_MESSAGE - Schedule the message with post_at timestamp Required]

Key parameters:

• channel: Resolved channel ID
• post_at: Unix timestamp for delivery (up to 120 days in advance)
• text / blocks: Message content

Pitfalls:

• Scheduling is limited to 120 days in advance
• post_at must be a Unix timestamp, not ISO 8601

Common Patterns

ID Resolution

Always resolve display names to IDs before operations:

• Channel name -> Channel ID: SLACK_FIND_CHANNELS with query param
• User name -> User ID: SLACK_FIND_USERS with search_query or email
• DM channel: SLACK_OPEN_DM with resolved user IDs

Pagination

Most list endpoints use cursor-based pagination:

• Follow response_metadata.next_cursor until empty
• Set explicit limit values (e.g., 100-200) for reliable paging
• De-duplicate results by id across pages

Message Formatting

• Prefer markdown_text over text or blocks for formatted messages
• Use <@USER_ID> format to mention users (not @username)
• Use \n for line breaks in markdown_text

Known Pitfalls

• Channel resolution: SLACK_FIND_CHANNELS can return empty results if channel is private and bot hasn't been invited
• Rate limits: SLACK_LIST_ALL_USERS and other list endpoints can hit HTTP 429; honor Retry-After header
• Nested responses: Results may be nested under response.data.results[0].response.data in wrapped executions
• Thread vs channel: SLACK_FETCH_CONVERSATION_HISTORY returns main timeline only; use SLACK_FETCH_MESSAGE_THREAD_FROM_A_CONVERSATION for thread replies
• Message editing: Requires both channel and original message ts; persist these from SEND_MESSAGE response
• Search delays: Recently posted messages may not appear in search results immediately
• Scope limitations: Missing OAuth scopes can cause 403 errors; check with SLACK_GET_APP_PERMISSION_SCOPES

Quick Reference

| Task | Tool Slug | Key Params | |------|-----------|------------| | Find channels | SLACK_FIND_CHANNELS | query | | List all channels | SLACK_LIST_ALL_CHANNELS | limit, cursor, types | | Send message | SLACK_SEND_MESSAGE | channel, markdown_text | | Edit message | SLACK_UPDATES_A_SLACK_MESSAGE | channel, ts, markdown_text | | Search messages | SLACK_SEARCH_MESSAGES | query, count, sort | | Get thread | SLACK_FETCH_MESSAGE_THREAD_FROM_A_CONVERSATION | channel, ts | | Add reaction | SLACK_ADD_REACTION_TO_AN_ITEM | channel, name, timestamp | | Find users | SLACK_FIND_USERS | search_query or email | | List users | SLACK_LIST_ALL_USERS | limit, cursor | | Open DM | SLACK_OPEN_DM | user IDs | | Schedule message | SLACK_SCHEDULE_MESSAGE | channel, post_at, text | | Get channel info | SLACK_RETRIEVE_CONVERSATION_INFORMATION | channel ID | | Channel history | SLACK_FETCH_CONVERSATION_HISTORY | channel, oldest, latest | | Workspace info | SLACK_FETCH_TEAM_INFO | (none) |

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