Slack Automation via Rube MCP

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

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)

When to Use

This skill is applicable to execute the workflow or actions described in the overview.