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Slack MCP Server

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Slack MCP Server

AgenticLedger Platform Integration Version: 1.0.0

Overview

The Slack MCP Server enables AI agents to interact with Slack workspaces through standardized Model Context Protocol (MCP) tools. This server provides access to read messages, post updates, manage threads, and discover channels while following AgenticLedger platform security and authentication standards.

Verified with real Slack data - all core features tested and working! ✅

Related MCP server: Slack MCP Server

Authentication Pattern

✅ OAuth (Direct access token)

This server uses Slack's OAuth tokens directly. The platform handles the OAuth flow and token management - the server simply receives and uses the access token.

Token Format

accessToken: "xoxb-..." // Bot token (recommended)

Required Slack Scopes

Your Slack app needs these OAuth scopes:

Required for core functionality:

  • channels:history - View messages in public channels

  • groups:history - View messages in private channels

  • im:history - View messages in direct messages

  • mpim:history - View messages in group direct messages

  • channels:read - View basic channel information

  • groups:read - View basic private channel information

  • users:read - View user information

  • chat:write - Post messages to channels and conversations

Available Tools

1. conversations_history

Description: Retrieves message history from a Slack channel, DM, or thread with pagination support

✅ Tested and working with real Slack data!

Parameters:

  • accessToken (string, required): Slack OAuth token (xoxb-...)

  • channel_id (string, required): Channel ID (e.g., C1234567890), channel name (#general), or DM (@username)

  • limit (string|number, optional): Time range (1d, 7d, 1m, 90d) or message count (e.g., 100)

  • cursor (string, optional): Pagination cursor from previous response

  • include_activity_messages (boolean, optional): Include join/leave system messages (default: false)

Example:

{
  "accessToken": "xoxb-...",
  "channel_id": "#testing",
  "limit": 10
}

Response:

{
  "success": true,
  "data": {
    "messages": [
      {
        "type": "message",
        "user": "U1234567890",
        "text": "Hello world!",
        "ts": "1234567890.123456"
      }
    ],
    "has_more": false,
    "cursor": "",
    "channel_id": "C1234567890"
  }
}

2. conversations_replies

Description: Fetches all messages in a specific thread by channel and thread timestamp

✅ Tested and working with real threads!

Parameters:

  • accessToken (string, required): Slack OAuth token

  • channel_id (string, required): Channel ID, name (#general), or DM (@username)

  • thread_ts (string, required): Message timestamp in format 1234567890.123456

  • limit (string|number, optional): Time range or message count

  • cursor (string, optional): Pagination cursor

  • include_activity_messages (boolean, optional): Include system messages (default: false)

Example:

{
  "accessToken": "xoxb-...",
  "channel_id": "#testing",
  "thread_ts": "1234567890.123456",
  "limit": 50
}

Response:

{
  "success": true,
  "data": {
    "messages": [
      {
        "type": "message",
        "user": "U1234567890",
        "text": "Thread parent message",
        "ts": "1234567890.123456",
        "thread_ts": "1234567890.123456"
      },
      {
        "type": "message",
        "user": "U9876543210",
        "text": "Thread reply",
        "ts": "1234567890.234567",
        "thread_ts": "1234567890.123456"
      }
    ],
    "has_more": false,
    "channel_id": "C1234567890",
    "thread_ts": "1234567890.123456"
  }
}

3. conversations_add_message

Description: Posts a message to a channel, thread, or DM. Supports markdown and plain text formatting.

✅ Tested and working - posts to both channels and threads!

⚠️ SAFETY NOTE: This tool is disabled by default. To enable, set the SLACK_MCP_ADD_MESSAGE_TOOL environment variable to:

  • * - Enable for all channels

  • C1234567890,C9876543210 - Enable for specific channel IDs (comma-separated)

Parameters:

  • accessToken (string, required): Slack OAuth token with chat:write scope

  • channel_id (string, required): Target channel ID, name (#general), or DM (@username)

  • thread_ts (string, optional): Thread timestamp; omit to post to channel directly

  • payload (string, required): Message content to post

  • content_type (string, optional): "text/markdown" (default) or "text/plain"

Example - Post to channel:

{
  "accessToken": "xoxb-...",
  "channel_id": "#general",
  "payload": "Hello from AI agent! 👋",
  "content_type": "text/markdown"
}

Example - Post to thread:

{
  "accessToken": "xoxb-...",
  "channel_id": "#general",
  "thread_ts": "1234567890.123456",
  "payload": "Reply in thread"
}

Response:

{
  "success": true,
  "data": {
    "ok": true,
    "channel": "C1234567890",
    "ts": "1234567890.123456",
    "message": {
      "text": "Hello from AI agent! 👋",
      "type": "message"
    }
  }
}

4. channels_list

Description: Lists workspace channels by type (public, private, DMs, group DMs) with optional popularity sorting

✅ Tested and working with real workspace data!

Parameters:

  • accessToken (string, required): Slack OAuth token

  • channel_types (string, required): Comma-separated values: mpim, im, public_channel, private_channel

  • sort (string, optional): "popularity" to sort by member count

  • limit (number, optional): Number of results (max: 999, default: 100)

  • cursor (string, optional): Pagination cursor

Example:

{
  "accessToken": "xoxb-...",
  "channel_types": "public_channel,private_channel",
  "sort": "popularity",
  "limit": 50
}

Response:

{
  "success": true,
  "data": {
    "channels": [
      {
        "id": "C1234567890",
        "name": "general",
        "topic": "Company-wide announcements",
        "purpose": "This channel is for team-wide communication",
        "member_count": 150,
        "is_private": false,
        "is_channel": true,
        "is_im": false,
        "is_mpim": false
      }
    ],
    "has_more": false
  }
}

Installation

# Install dependencies
npm install

# Build the TypeScript project
npm run build

# Run the server
npm start

Testing

# Run all tests
npm test

# Run integration tests (requires valid Slack token)
npm run test:integration

Platform Integration Notes

Environment Variables

  • SLACK_MCP_ADD_MESSAGE_TOOL - Controls message posting capability:

    • Not set (default): Message posting disabled

    • *: Enable for all channels

    • C123...,C456...: Enable for specific channel IDs

Error Handling

The server provides specific error messages for common Slack API errors:

  • channel_not_found → "Channel not found with the provided ID"

  • invalid_auth → "Invalid or expired authentication credentials"

  • not_in_channel → "Bot is not a member of this channel"

  • missing_scope → "Token is missing required Slack permissions/scopes"

  • rate_limited → "Rate limited by Slack API - please try again later"

Rate Limiting

Slack API has rate limits. The server handles rate limit errors gracefully, but consider implementing retry logic in your agent code.

Channel ID Resolution

The server automatically resolves:

  • Channel names: #general → C1234567890

  • DM usernames: @username → Opens/finds DM and returns channel ID

  • Direct IDs: C1234567890 → Used as-is

Technical Specifications

  • Node.js version: ≥18.0.0

  • Dependencies:

    • @slack/web-api - Official Slack Web API client

    • @modelcontextprotocol/sdk - MCP protocol implementation

    • zod - Schema validation

  • Language: TypeScript (ES2022)

  • Transport: Stdio (MCP standard)

Known Limitations

  1. Bot Channel Membership: Bot must be added to channels before reading messages (use /invite @bot-name in Slack)

  2. Message Posting Safety: Disabled by default - requires explicit environment variable configuration

  3. Rate Limits: Slack enforces rate limits on API calls - implement retry logic for production use

Real-World Testing Results

This server has been tested with actual Slack workspace data:

Verified Capabilities:

  • ✅ Read 5+ messages from real channels

  • ✅ Read 2-message threads successfully

  • ✅ Posted messages to channels (tested live)

  • ✅ Posted threaded replies (tested live)

  • ✅ Listed 12 real workspace channels

  • ✅ Sorted channels by popularity (614 → 143 → 23 members...)

  • ✅ All error handling tested with real errors

  • ✅ Performance under 300ms for all operations

What Works:

  • 4/4 tools fully functional with real Slack API ✅

  • All core reading and writing capabilities verified ✅

  • Channel discovery and management working ✅

See REAL_TEST_RESULTS.md for complete testing documentation.

Platform Configuration Recommendations

For AgenticLedger Integration:

  1. OAuth Setup: Configure your Slack OAuth app with the required scopes listed above

  2. Token Storage: Store tokens securely in the platform's credential management system

  3. Rate Limiting: Implement platform-level rate limiting and retry logic

  4. Error Monitoring: Monitor for authentication and permission errors

  5. Audit Logging: Log all message posting operations for compliance

Built for AgenticLedger Platform Follows MCP Server Build Guide v1.0.0 Real-world tested and verified ✅

Available Tools

4 tools
channels_listA

Lists workspace channels by type (public, private, DMs, group DMs) with optional popularity sorting. Supports pagination.

ParametersJSON Schema
NameRequiredDescriptionDefault
accessTokenYesSlack OAuth token (xoxp-... or xoxb-...)
channel_typesYesComma-separated channel types: mpim, im, public_channel, private_channel
sortNoSort by member count (popularity)
limitNoNumber of results (max: 999, default: 100)
cursorNoPagination cursor from previous response

TDQS

A3.5/5.0
Behavior3/5

Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

With no annotations provided, the description carries the full burden of behavioral disclosure. It mentions pagination and sorting, which are useful behavioral traits, but does not cover critical aspects like authentication requirements (implied by accessToken but not explained), rate limits, error handling, or what the output looks like. It adds some context but leaves significant gaps for a tool with multiple parameters and no output schema.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Conciseness5/5

Is the description appropriately sized, front-loaded, and free of redundancy?

The description is a single, well-structured sentence that efficiently covers the tool's purpose, types, and key features (sorting, pagination) without unnecessary words. It is front-loaded with the main action and resource, making it easy to scan and understand quickly.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Completeness3/5

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

Given the complexity (5 parameters, no annotations, no output schema), the description is incomplete. It covers the basic purpose and some features but lacks details on authentication, error handling, output format, and explicit differentiation from siblings. While concise, it does not fully compensate for the missing structured data, leaving the agent with insufficient context for optimal use.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Parameters3/5

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

The schema description coverage is 100%, so the schema already documents all parameters thoroughly. The description adds minimal value beyond the schema by mentioning 'popularity sorting' (implied by the sort parameter) and 'pagination' (implied by cursor), but does not provide additional syntax, format details, or usage examples. This meets the baseline for high schema coverage.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Purpose4/5

Does the description clearly state what the tool does and how it differs from similar tools?

The description clearly states the action ('Lists') and resource ('workspace channels'), specifying the types (public, private, DMs, group DMs) and optional features (popularity sorting, pagination). However, it does not explicitly differentiate from sibling tools like conversations_history or conversations_replies, which focus on message retrieval rather than channel listing, leaving some ambiguity in tool selection.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Usage Guidelines3/5

Does the description explain when to use this tool, when not to, or what alternatives exist?

The description implies usage for listing channels with type filtering and sorting, but provides no explicit guidance on when to use this tool versus alternatives like conversations_history for message access. It mentions 'optional popularity sorting' and 'pagination' as features, which hints at context but lacks clear when/when-not instructions or named alternatives.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.

conversations_add_messageA

Posts a message to a channel, thread, or DM. Supports markdown and plain text. NOTE: Disabled by default for safety - set SLACK_MCP_ADD_MESSAGE_TOOL environment variable to enable.

ParametersJSON Schema
NameRequiredDescriptionDefault
accessTokenYesSlack OAuth token (xoxp-... or xoxb-...) with chat:write scope
channel_idYesTarget channel ID, name (#general), or DM (@username)
thread_tsNoThread timestamp; omit to post to channel directly
payloadYesMessage content to post
content_typeNoContent format (default: text/markdown)

TDQS

A3.9/5.0
Behavior4/5

Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

With no annotations provided, the description carries the full burden of behavioral disclosure. It effectively communicates critical behavioral traits: the safety restriction (disabled by default requiring environment variable), the mutation nature ('Posts a message'), and format support (markdown/plain text). However, it lacks details about rate limits, error conditions, or response format that would be helpful for a write operation.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Conciseness5/5

Is the description appropriately sized, front-loaded, and free of redundancy?

The description is extremely concise with only two sentences, both of which earn their place. The first sentence establishes core functionality, the second provides critical safety information. No wasted words, and the most important information (the tool's purpose) is front-loaded.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Completeness3/5

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

For a mutation tool with no annotations and no output schema, the description provides basic but incomplete context. It covers the core action and safety restriction adequately, but lacks information about return values, error handling, permissions beyond the token scope mentioned in the schema, or how it differs from potential alternative messaging approaches. The safety note is valuable but doesn't fully compensate for missing behavioral details.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Parameters3/5

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

With 100% schema description coverage, the input schema already documents all 5 parameters thoroughly. The description adds no additional parameter semantics beyond what's in the schema - it doesn't explain parameter relationships, provide examples, or clarify edge cases. The baseline score of 3 reflects adequate but minimal value addition from the description.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Purpose5/5

Does the description clearly state what the tool does and how it differs from similar tools?

The description clearly states the specific action ('Posts a message') and target resources ('to a channel, thread, or DM'), distinguishing it from sibling tools like channels_list (listing) or conversations_history (reading). It includes additional functionality details ('Supports markdown and plain text') that further clarify its purpose beyond basic posting.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Usage Guidelines3/5

Does the description explain when to use this tool, when not to, or what alternatives exist?

The description implies usage context through the safety note about being disabled by default, but does not explicitly state when to use this tool versus alternatives. No guidance is provided on when to choose this tool over other messaging approaches or sibling tools, leaving usage decisions to inference from the purpose statement alone.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.

conversations_historyB

Retrieves message history from a Slack channel, DM, or thread. Supports pagination and filtering.

ParametersJSON Schema
NameRequiredDescriptionDefault
accessTokenYesSlack OAuth token (xoxp-... or xoxb-...)
channel_idYesChannel ID (e.g., C1234567890), channel name (#general), or DM (@username)
limitNoTime range (1d, 7d, 1m, 90d) or message count (e.g., 100)
cursorNoPagination cursor from previous response
include_activity_messagesNoInclude join/leave system messages (default: false)

TDQS

B3.2/5.0
Behavior2/5

Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

No annotations are provided, so the description carries the full burden of behavioral disclosure. It mentions 'Supports pagination and filtering,' which adds some context beyond the input schema, but it doesn't cover critical aspects like authentication needs (implied by 'accessToken' but not explained), rate limits, error handling, or what the output looks like (e.g., message format). For a tool with 5 parameters and no annotations, this is a significant gap in transparency.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Conciseness5/5

Is the description appropriately sized, front-loaded, and free of redundancy?

The description is highly concise and well-structured: two sentences that front-load the core purpose ('Retrieves message history...') and follow with key features ('Supports pagination and filtering'). Every word earns its place, with no redundancy or fluff, making it easy to scan and understand quickly.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Completeness2/5

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

Given the tool's complexity (5 parameters, no annotations, no output schema), the description is incomplete. It lacks details on authentication requirements, output format (e.g., what data is returned), error conditions, or how pagination/filtering work in practice. While it states the purpose clearly, it doesn't provide enough context for an agent to use the tool effectively without relying heavily on the input schema and external knowledge.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Parameters3/5

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema description coverage is 100%, meaning all parameters are documented in the input schema. The description doesn't add any specific parameter details beyond what's in the schema (e.g., it doesn't explain 'limit' formats or 'cursor' usage further). Since the schema handles the heavy lifting, the baseline score of 3 is appropriate, as the description provides no extra parameter semantics.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Purpose4/5

Does the description clearly state what the tool does and how it differs from similar tools?

The description clearly states the tool's purpose: 'Retrieves message history from a Slack channel, DM, or thread.' It specifies the verb ('retrieves'), resource ('message history'), and scope ('Slack channel, DM, or thread'), making it easy to understand what the tool does. However, it doesn't explicitly differentiate from sibling tools like 'conversations_replies' (which might retrieve thread-specific replies), leaving room for slight ambiguity.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Usage Guidelines3/5

Does the description explain when to use this tool, when not to, or what alternatives exist?

The description implies usage by mentioning 'Supports pagination and filtering,' which suggests it's for retrieving historical messages with optional controls. However, it doesn't provide explicit guidance on when to use this tool versus alternatives like 'conversations_replies' (for thread replies) or 'channels_list' (for listing channels). No exclusions or prerequisites are stated, leaving usage context somewhat inferred.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.

conversations_repliesA

Fetches all messages in a specific thread by channel and thread timestamp. Supports pagination.

ParametersJSON Schema
NameRequiredDescriptionDefault
accessTokenYesSlack OAuth token (xoxp-... or xoxb-...)
channel_idYesChannel ID (e.g., C1234567890), channel name (#general), or DM (@username)
thread_tsYesMessage timestamp in format 1234567890.123456
limitNoTime range (1d, 7d, 1m, 90d) or message count (e.g., 100)
cursorNoPagination cursor from previous response
include_activity_messagesNoInclude join/leave system messages (default: false)

TDQS

A3.5/5.0
Behavior3/5

Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

With no annotations provided, the description carries the full burden of behavioral disclosure. It mentions pagination support, which is valuable behavioral context. However, it doesn't disclose other important traits like rate limits, authentication requirements (though schema covers token), error conditions, or response format details.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Conciseness5/5

Is the description appropriately sized, front-loaded, and free of redundancy?

The description is extremely concise (two sentences) with zero wasted words. It's front-loaded with the core purpose and follows with important behavioral information about pagination. Every sentence earns its place.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Completeness3/5

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

For a read operation with 6 parameters and no output schema, the description provides adequate but minimal context. It covers the core purpose and pagination behavior but lacks details about response format, error handling, or how results are structured. With no annotations and no output schema, more completeness would be beneficial.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Parameters3/5

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema description coverage is 100%, so the schema already documents all 6 parameters thoroughly. The description adds minimal value beyond the schema - it mentions 'channel and thread timestamp' which maps to channel_id and thread_ts parameters, but doesn't provide additional semantic context beyond what's in the parameter descriptions.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Purpose4/5

Does the description clearly state what the tool does and how it differs from similar tools?

The description clearly states the action ('fetches all messages') and target resource ('in a specific thread by channel and thread timestamp'), providing a specific verb+resource combination. However, it doesn't explicitly differentiate from sibling tools like conversations_history, which might also fetch messages but from different contexts.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Usage Guidelines3/5

Does the description explain when to use this tool, when not to, or what alternatives exist?

The description implies usage context ('specific thread') but doesn't explicitly state when to use this tool versus alternatives like conversations_history (for channel messages) or conversations_add_message (for adding messages). No explicit exclusions or prerequisites are mentioned.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.

Tool Schema Changelog

Recent tool additions, removals, and schema changes observed during successful MCP inspections. Dates show when Glama detected each change.

  1. 4 tool updates
    • First observedchannels_list
    • First observedconversations_add_message
    • First observedconversations_history
    • First observedconversations_replies
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TDQS

B3.4/5.0
Disambiguation5/5

Each tool has a clearly distinct purpose: channels_list lists channels, conversations_add_message posts messages, conversations_history retrieves channel history, and conversations_replies fetches thread replies. There is no overlap in functionality, making it easy for an agent to select the correct tool.

Naming Consistency4/5

The tool names follow a consistent snake_case pattern and use descriptive verbs like 'list', 'add', and 'history'. However, 'channels_list' deviates slightly from the 'conversations_' prefix used by the other three tools, which is a minor inconsistency.

Tool Count3/5

With only 4 tools, the server feels thin for a Slack integration, as it lacks common operations like updating or deleting messages, managing users, or handling reactions. While the tools cover basic messaging and channel listing, the scope is limited, potentially requiring workarounds for full Slack workflows.

Completeness2/5

The tool set is significantly incomplete for a Slack server. It covers listing channels and basic message operations (posting, retrieving history, and thread replies), but misses essential CRUD actions like editing or deleting messages, user management, file handling, and event subscriptions. This will likely cause agent failures in more complex interactions.

Maintenance

ActivityInactive
ResponsivenessSyncing

Resources

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