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.

• Verify Rube MCP is available by confirming RUBE_SEARCH_TOOLS responds

• Call RUBE_MANAGE_CONNECTIONS with toolkit slack

• If connection is not ACTIVE, follow the returned auth link to complete Slack OAuth

• 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:

• SLACK_FIND_CHANNELS

• Resolve channel name to channel ID [Prerequisite]

• SLACK_LIST_ALL_CHANNELS

• Fallback if FIND_CHANNELS returns empty/ambiguous results [Fallback]

• SLACK_FIND_USERS

• Resolve user for DMs or @mentions [Optional]

• SLACK_OPEN_DM

• Open/reuse a DM channel if messaging a user directly [Optional]

• SLACK_SEND_MESSAGE

• Post the message with resolved channel ID [Required]

• 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:

• SLACK_FIND_CHANNELS

• Resolve channel for scoped search with in:#channel [Optional]

• SLACK_FIND_USERS

• Resolve user for author filter with from:@user [Optional]

• SLACK_SEARCH_MESSAGES

• Run keyword search across accessible conversations [Required]

• 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:

• SLACK_FETCH_TEAM_INFO

• Validate connectivity and get workspace identity [Required]

• SLACK_LIST_ALL_CHANNELS

• Enumerate public channels [Required]

• SLACK_LIST_CONVERSATIONS

• Include private channels and DMs [Optional]

• SLACK_LIST_ALL_USERS

• List workspace members [Required]

• SLACK_RETRIEVE_CONVERSATION_INFORMATION

• Get detailed channel metadata [Optional]

• 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:

• SLACK_SEARCH_MESSAGES or SLACK_FETCH_CONVERSATION_HISTORY

• Find the target message [Prerequisite]

• SLACK_ADD_REACTION_TO_AN_ITEM

• Add an emoji reaction [Required]

• SLACK_FETCH_ITEM_REACTIONS

• List reactions on a message [Optional]

• SLACK_REMOVE_REACTION_FROM_ITEM

• Remove a reaction [Optional]

• SLACK_SEND_MESSAGE

• Reply in thread using thread_ts [Optional]

• 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:

• SLACK_FIND_CHANNELS

• Resolve channel ID [Prerequisite]

• 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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