Slack MCP Server

Setup Guide

• Authentication Setup
• Installation
• Configuration and Usage

Environment Variables (Quick Reference)

Variable	Required?	Default	Description
SLACK_MCP_XOXC_TOKEN	Yes*	nil	Slack browser token (xoxc-...)
SLACK_MCP_XOXD_TOKEN	Yes*	nil	Slack browser cookie d (xoxd-...)
SLACK_MCP_XOXP_TOKEN	Yes*	nil	User OAuth token (xoxp-...) — alternative to xoxc/xoxd
SLACK_MCP_XOXB_TOKEN	Yes*	nil	Bot token (xoxb-...) — alternative to xoxp/xoxc/xoxd. Bot has limited access (invited channels only, no search)
SLACK_MCP_PORT	No	13080	Port for the MCP server to listen on
SLACK_MCP_HOST	No	127.0.0.1	Host for the MCP server to listen on
SLACK_MCP_API_KEY	No	nil	Bearer token for SSE and HTTP transports
SLACK_MCP_PROXY	No	nil	Proxy URL for outgoing requests
SLACK_MCP_USER_AGENT	No	nil	Custom User-Agent (for Enterprise Slack environments)
SLACK_MCP_CUSTOM_TLS	No	nil	Send custom TLS-handshake to Slack servers based on SLACK_MCP_USER_AGENT or default User-Agent. (for Enterprise Slack environments)
SLACK_MCP_SERVER_CA	No	nil	Path to CA certificate
SLACK_MCP_SERVER_CA_TOOLKIT	No	nil	Inject HTTPToolkit CA certificate to root trust-store for MitM debugging
SLACK_MCP_SERVER_CA_INSECURE	No	false	Trust all insecure requests (NOT RECOMMENDED)
SLACK_MCP_ADD_MESSAGE_TOOL	No	nil	Enable message posting via conversations_add_message by setting it to true for all channels, a comma-separated list of channel IDs to whitelist specific channels, or use ! before a channel ID to allow all except specified ones. If empty, the tool is only registered when explicitly listed in SLACK_MCP_ENABLED_TOOLS.
SLACK_MCP_ADD_MESSAGE_MARK	No	nil	When conversations_add_message is enabled (via SLACK_MCP_ADD_MESSAGE_TOOL or SLACK_MCP_ENABLED_TOOLS), setting this to true will automatically mark sent messages as read.
SLACK_MCP_ADD_MESSAGE_UNFURLING	No	nil	Enable to let Slack unfurl posted links or set comma-separated list of domains e.g. github.com,slack.com to whitelist unfurling only for them. If text contains whitelisted and unknown domain unfurling will be disabled for security reasons.
SLACK_MCP_REACTION_TOOL	No	nil	Enable reactions_add and reactions_remove tools by setting to true for all channels, a comma-separated list of channel IDs to whitelist specific channels, or use ! before a channel ID to allow all except specified ones. If empty, the tools are only registered when explicitly listed in SLACK_MCP_ENABLED_TOOLS.
SLACK_MCP_ATTACHMENT_TOOL	No	nil	Enable the attachment_get_data tool by setting to true, 1, or yes. Does not support channel-level restrictions. If empty, the tool is only registered when explicitly listed in SLACK_MCP_ENABLED_TOOLS.
SLACK_MCP_MARK_TOOL	No	nil	Enable the conversations_mark tool by setting to true or 1. Disabled by default to prevent accidental marking of messages as read.
SLACK_MCP_USERS_CACHE	No	~/Library/Caches/slack-mcp-server/users_cache.json (macOS) ~/.cache/slack-mcp-server/users_cache.json (Linux) %LocalAppData%/slack-mcp-server/users_cache.json (Windows)	Path to the users cache file. Used to cache Slack user information to avoid repeated API calls on startup.
SLACK_MCP_CHANNELS_CACHE	No	~/Library/Caches/slack-mcp-server/channels_cache_v2.json (macOS) ~/.cache/slack-mcp-server/channels_cache_v2.json (Linux) %LocalAppData%/slack-mcp-server/channels_cache_v2.json (Windows)	Path to the channels cache file. Used to cache Slack channel information to avoid repeated API calls on startup.
SLACK_MCP_LOG_LEVEL	No	info	Log-level for stdout or stderr. Valid values are: debug, info, warn, error, panic and fatal
SLACK_MCP_GOVSLACK	No	nil	Set to true to enable GovSlack mode. Routes API calls to slack-gov.com endpoints instead of slack.com for FedRAMP-compliant government workspaces.
SLACK_MCP_ENABLED_TOOLS	No	nil	Comma-separated list of tools to register. If empty, all read-only tools and usergroups tools are registered; write tools (conversations_add_message, reactions_add, reactions_remove, attachment_get_data) require their specific env var OR must be explicitly listed here. When a write tool is listed here, it's enabled without channel restrictions. Available tools: conversations_history, conversations_replies, conversations_add_message, reactions_add, reactions_remove, attachment_get_data, conversations_search_messages, channels_list, usergroups_list, usergroups_me, usergroups_create, usergroups_update, usergroups_users_update.

*You need one of: xoxp (user), xoxb (bot), or both xoxc/xoxd tokens for authentication.

Limitations matrix & Cache

Users Cache	Channels Cache	Limitations
:x:	:x:	No cache, No LLM context enhancement with user data, tool channels_list will be fully not functional. Tools conversations_* will have limited capabilities and you won't be able to search messages by @userHandle or #channel-name, getting messages by @userHandle or #channel-name won't be available either.
:white_check_mark:	:x:	No channels cache, tool channels_list will be fully not functional. Tools conversations_* will have limited capabilities and you won't be able to search messages by @userHandle or #channel-name, getting messages by @userHandle or #channel-name won't be available either.
:white_check_mark:	:white_check_mark:	No limitations, fully functional Slack MCP Server.

Debugging Tools

# Run the inspector with stdio transport
npx @modelcontextprotocol/inspector go run mcp/mcp-server.go --transport stdio

# View logs
tail -n 20 -f ~/Library/Logs/Claude/mcp*.log

claude mcp add slack -e SLACK_MCP_XOXP_TOKEN=xoxp-... -- npx -y slack-mcp-server@latest --transport stdio

{
  "mcpServers": {
    "slack": {
      "command": "npx",
      "args": [
        "-y",
        "slack-mcp-server@latest",
        "--transport",
        "stdio"
      ],
      "env": {
        "SLACK_MCP_XOXP_TOKEN": "xoxp-..."
      }
    }
  }
}

{
  "mcpServers": {
    "slack": {
      "command": "npx",
      "args": [
        "-y",
        "slack-mcp-server@latest",
        "--transport",
        "stdio"
      ],
      "env": {
        "SLACK_MCP_XOXP_TOKEN": "xoxp-..."
      }
    }
  }
}

{
  "servers": {
    "slack": {
      "type": "stdio",
      "command": "npx",
      "args": [
        "-y",
        "slack-mcp-server@latest",
        "--transport",
        "stdio"
      ],
      "env": {
        "SLACK_MCP_XOXP_TOKEN": "xoxp-..."
      }
    }
  }
}

{
  "mcpServers": {
    "slack": {
      "command": "npx",
      "args": [
        "-y",
        "slack-mcp-server@latest",
        "--transport",
        "stdio"
      ],
      "env": {
        "SLACK_MCP_XOXP_TOKEN": "xoxp-..."
      }
    }
  }
}

Slack MCP Server

Model Context Protocol (MCP) server for Slack Workspaces. The most powerful MCP Slack server — supports Stdio, SSE and HTTP transports, proxy settings, DMs, Group DMs, Smart History fetch (by date or count), may work via OAuth or in complete stealth mode with no permissions and scopes in Workspace 😏.

Important:
We need your support! Each month, over 30,000 engineers visit this repository, and more than 9,000 are already using it.

If you appreciate the work our contributors have put into this project, please consider giving the repository a star.

This feature-rich Slack MCP Server has:

• Stealth and OAuth Modes: Run the server without requiring additional permissions or bot installations (stealth mode), or use secure OAuth tokens for access without needing to refresh or extract tokens from the browser (OAuth mode).
• Enterprise Workspaces Support: Possibility to integrate with Enterprise Slack setups.
• Channel and Thread Support with #Name @Lookup: Fetch messages from channels and threads, including activity messages, and retrieve channels using their names (e.g., #general) as well as their IDs.
• Smart History: Fetch messages with pagination by date (d1, 7d, 1m) or message count.
• Unread Messages: Get all unread messages across channels efficiently with priority sorting (DMs > partner channels > internal), @mention filtering, and mark-as-read support.
• Search Messages: Search messages in channels, threads, and DMs using various filters like date, user, and content.
• Safe Message Posting: The conversations_add_message tool is disabled by default for safety. Enable it via an environment variable, with optional channel restrictions.
• DM and Group DM support: Retrieve direct messages and group direct messages.
• Embedded user information: Embed user information in messages, for better context.
• Cache support: Cache users and channels for faster access.
• Stdio/SSE/HTTP Transports & Proxy Support: Use the server with any MCP client that supports Stdio, SSE or HTTP transports, and configure it to route outgoing requests through a proxy if needed.

Analytics Demo

Add Message Demo

Tools

1. conversations_history:

Get messages from the channel (or DM) by channel_id, the last row/column in the response is used as 'cursor' parameter for pagination if not empty

• Parameters:
  • channel_id (string, required): - channel_id (string): ID of the channel in format Cxxxxxxxxxx or its name starting with #... or @... aka #general or @username_dm.
  • include_activity_messages (boolean, default: false): If true, the response will include activity messages such as channel_join or channel_leave. Default is boolean false.
  • cursor (string, optional): Cursor for pagination. Use the value of the last row and column in the response as next_cursor field returned from the previous request.
  • limit (string, default: "1d"): Limit of messages to fetch in format of maximum ranges of time (e.g. 1d - 1 day, 1w - 1 week, 30d - 30 days, 90d - 90 days which is a default limit for free tier history) or number of messages (e.g. 50). Must be empty when 'cursor' is provided.

2. conversations_replies:

Get a thread of messages posted to a conversation by channelID and thread_ts, the last row/column in the response is used as cursor parameter for pagination if not empty.

• Parameters:
  • channel_id (string, required): ID of the channel in format Cxxxxxxxxxx or its name starting with #... or @... aka #general or @username_dm.
  • thread_ts (string, required): Unique identifier of either a thread’s parent message or a message in the thread. ts must be the timestamp in format 1234567890.123456 of an existing message with 0 or more replies.
  • include_activity_messages (boolean, default: false): If true, the response will include activity messages such as 'channel_join' or 'channel_leave'. Default is boolean false.
  • cursor (string, optional): Cursor for pagination. Use the value of the last row and column in the response as next_cursor field returned from the previous request.
  • limit (string, default: "1d"): Limit of messages to fetch in format of maximum ranges of time (e.g. 1d - 1 day, 1w - 1 week, 30d - 30 days, 90d - 90 days which is a default limit for free tier history) or number of messages (e.g. 50). Must be empty when 'cursor' is provided.

3. conversations_add_message

Add a message to a public channel, private channel, or direct message (DM, or IM) conversation by channel_id and thread_ts.

Note: Posting messages is disabled by default for safety. To enable, set the SLACK_MCP_ADD_MESSAGE_TOOL environment variable. If set to a comma-separated list of channel IDs, posting is enabled only for those specific channels. See the Environment Variables section below for details.

• Parameters:
  • channel_id (string, required): ID of the channel in format Cxxxxxxxxxx or its name starting with #... or @... aka #general or @username_dm.
  • thread_ts (string, optional): Unique identifier of either a thread’s parent message or a message in the thread_ts must be the timestamp in format 1234567890.123456 of an existing message with 0 or more replies. Optional, if not provided the message will be added to the channel itself, otherwise it will be added to the thread.
  • payload (string, required): Message payload in specified content_type format. Example: 'Hello, world!' for text/plain or '# Hello, world!' for text/markdown.
  • content_type (string, default: "text/markdown"): Content type of the message. Default is 'text/markdown'. Allowed values: 'text/markdown', 'text/plain'.

4. conversations_search_messages

Search messages in a public channel, private channel, or direct message (DM, or IM) conversation using filters. All filters are optional, if not provided then search_query is required.

Note: This tool is not available when using bot tokens (xoxb-*). Bot tokens cannot use the search.messages API.

• Parameters:
  • search_query (string, optional): Search query to filter messages. Example: 'marketing report' or full URL of Slack message e.g. 'https://slack.com/archives/C1234567890/p1234567890123456', then the tool will return a single message matching given URL, herewith all other parameters will be ignored.
  • filter_in_channel (string, optional): Filter messages in a specific channel by its ID or name. Example: C1234567890 or #general. If not provided, all channels will be searched.
  • filter_in_im_or_mpim (string, optional): Filter messages in a direct message (DM) or multi-person direct message (MPIM) conversation by its ID or name. Example: D1234567890 or @username_dm. If not provided, all DMs and MPIMs will be searched.
  • filter_users_with (string, optional): Filter messages with a specific user by their ID or display name in threads and DMs. Example: U1234567890 or @username. If not provided, all threads and DMs will be searched.
  • filter_users_from (string, optional): Filter messages from a specific user by their ID or display name. Example: U1234567890 or @username. If not provided, all users will be searched.
  • filter_date_before (string, optional): Filter messages sent before a specific date in format YYYY-MM-DD. Example: 2023-10-01, July, Yesterday or Today. If not provided, all dates will be searched.
  • filter_date_after (string, optional): Filter messages sent after a specific date in format YYYY-MM-DD. Example: 2023-10-01, July, Yesterday or Today. If not provided, all dates will be searched.
  • filter_date_on (string, optional): Filter messages sent on a specific date in format YYYY-MM-DD. Example: 2023-10-01, July, Yesterday or Today. If not provided, all dates will be searched.
  • filter_date_during (string, optional): Filter messages sent during a specific period in format YYYY-MM-DD. Example: July, Yesterday or Today. If not provided, all dates will be searched.
  • filter_threads_only (boolean, default: false): If true, the response will include only messages from threads. Default is boolean false.
  • cursor (string, default: ""): Cursor for pagination. Use the value of the last row and column in the response as next_cursor field returned from the previous request.
  • limit (number, default: 20): The maximum number of items to return. Must be an integer between 1 and 100.

5. channels_list:

Get list of channels

• Parameters:
  • channel_types (string, required): Comma-separated channel types. Allowed values: mpim, im, public_channel, private_channel. Example: public_channel,private_channel,im
  • sort (string, optional): Type of sorting. Allowed values: popularity - sort by number of members/participants in each channel.
  • limit (number, default: 100): The maximum number of items to return. Must be an integer between 1 and 1000 (maximum 999).
  • cursor (string, optional): Cursor for pagination. Use the value of the last row and column in the response as next_cursor field returned from the previous request.

6. reactions_add:

Add an emoji reaction to a message in a public channel, private channel, or direct message (DM, or IM) conversation.

Note: Adding reactions is disabled by default for safety. To enable, set the SLACK_MCP_REACTION_TOOL environment variable. If set to a comma-separated list of channel IDs, reactions are enabled only for those specific channels. See the Environment Variables section below for details.

• Parameters:
  • channel_id (string, required): ID of the channel in format Cxxxxxxxxxx or its name starting with #... or @... aka #general or @username_dm.
  • timestamp (string, required): Timestamp of the message to add reaction to, in format 1234567890.123456.
  • emoji (string, required): The name of the emoji to add as a reaction (without colons). Example: thumbsup, heart, rocket.

7. reactions_remove:

Remove an emoji reaction from a message in a public channel, private channel, or direct message (DM, or IM) conversation.

Note: Removing reactions follows the same permission model as reactions_add. To enable, set the SLACK_MCP_REACTION_TOOL environment variable.

• Parameters:
  • channel_id (string, required): ID of the channel in format Cxxxxxxxxxx or its name starting with #... or @... aka #general or @username_dm.
  • timestamp (string, required): Timestamp of the message to remove reaction from, in format 1234567890.123456.
  • emoji (string, required): The name of the emoji to remove as a reaction (without colons). Example: thumbsup, heart, rocket.

8. users_search:

Search for users by name, email, or display name. Returns user details and DM channel ID if available.

Note: For OAuth tokens (xoxp/xoxb), this tool searches the local users cache using pattern matching. For browser session tokens (xoxc/xoxd), it uses the Slack edge API for real-time search.

• Parameters:

  • query (string, required): Search query - matches against real name, display name, username, or email.
  • limit (number, default: 10): Maximum number of results to return (1-100).

• Returns: CSV with fields:

  • UserID: User ID (e.g., U1234567890)
  • UserName: Slack username
  • RealName: User's real name
  • DisplayName: User's display name
  • Email: User's email address
  • Title: User's job title
  • DMChannelID: DM channel ID if available in cache (for quick messaging)

9. usergroups_list:

List all user groups (subteams) in the workspace.

• Parameters:

  • include_users (boolean, default: false): Include list of user IDs in each group.
  • include_count (boolean, default: true): Include user count for each group.
  • include_disabled (boolean, default: false): Include disabled/archived groups.

• Returns: CSV with fields: id, name, handle, description, user_count, is_external

Required OAuth scopes: usergroups:read

10. usergroups_create:

Create a new user group in the workspace.

• Parameters:

  • name (string, required): Name of the user group (e.g., "Engineering Team").
  • handle (string, optional): Mention handle without @ (e.g., "engineering"). If not provided, Slack will auto-generate one.
  • description (string, optional): Purpose or description of the group.
  • channels (string, optional): Comma-separated channel IDs for default channels where group mentions will be highlighted.

• Returns: JSON with created group details (id, name, handle, description)

Required OAuth scopes: usergroups:write

11. usergroups_update:

Update an existing user group's metadata.

• Parameters:

  • usergroup_id (string, required): ID of the user group (e.g., "S1234567890").
  • name (string, optional): New name for the group.
  • handle (string, optional): New mention handle.
  • description (string, optional): New description.
  • channels (string, optional): New default channels (comma-separated IDs). This replaces existing default channels.

• Returns: JSON with updated group details

Required OAuth scopes: usergroups:write

12. usergroups_users_update:

Update the members of a user group. This replaces all existing members.

• Parameters:

  • usergroup_id (string, required): ID of the user group (e.g., "S1234567890").
  • users (string, required): Comma-separated user IDs to set as members (e.g., "U123,U456,U789").

• Returns: JSON with updated group details including new user list

Required OAuth scopes: usergroups:write

13. usergroups_me:

Manage your user group membership: list groups you're in, join a group, or leave a group.

• Parameters:

  • action (string, required): Action to perform - list to see your groups, join to add yourself, leave to remove yourself.
  • usergroup_id (string, optional): ID of the user group (e.g., "S1234567890"). Required for join and leave actions.

• Returns:

  • For list: CSV with groups you're a member of
  • For join/leave: JSON with result message and updated group info

Required OAuth scopes: usergroups:read (for list), usergroups:read + usergroups:write (for join/leave)

14. conversations_unreads

Get unread messages across all channels efficiently. Uses a single API call to identify channels with unreads, then fetches only those messages. Results are prioritized: DMs > partner channels (Slack Connect) > internal channels.

Note: This tool works best with browser session tokens (xoxc/xoxd), which use the efficient client.counts API. For standard OAuth tokens (xoxp), a fallback method using conversations.info is used, which requires one API call per channel and may be slower for large workspaces. Not available with bot tokens (xoxb).

• Parameters:
  • include_messages (boolean, default: true): If true, returns the actual unread messages. If false, returns only a summary of channels with unreads.
  • channel_types (string, default: "all"): Filter by channel type: all, dm (direct messages), group_dm (group DMs), partner (externally shared channels), internal (regular workspace channels).
  • max_channels (number, default: 50): Maximum number of channels to fetch unreads from.
  • max_messages_per_channel (number, default: 10): Maximum messages to fetch per channel.
  • mentions_only (boolean, default: false): If true, only returns channels where you have @mentions. Note: This filter only works with browser tokens; OAuth tokens will return all unread channels.

15. conversations_mark

Mark a channel or DM as read.

Note: Marking messages as read is disabled by default for safety. To enable, set the SLACK_MCP_MARK_TOOL environment variable to true or 1. See the Environment Variables section below for details.

• Parameters:
  • channel_id (string, required): ID of the channel in format Cxxxxxxxxxx or its name starting with #... or @... (e.g., #general, @username).
  • ts (string, optional): Timestamp of the message to mark as read up to. If not provided, marks all messages as read.

16. saved_list

List saved items from Slack's "Save for Later" panel. Returns items the user has saved, with optional message content. This replaces the deprecated stars.list API (changelog).

Note: This tool requires browser session tokens (xoxc/xoxd). It is not available with standard OAuth (xoxp) or bot (xoxb) tokens.

• Parameters:
  • filter (string, default "saved"): Filter saved items: "saved" (active/in-progress), "completed" (marked done), "archived".
  • limit (number, default 50): Maximum number of items to return. Auto-paginates.
  • include_messages (boolean, default true): If true, fetches the actual saved message content. If false, returns metadata only.
  • max_messages_per_item (number, default 5): Max messages to fetch per saved item (for thread replies).

17. saved_update

Update a saved item: mark as completed, set a due date/reminder, or both. Use item_id and ts values from saved_list output. This replaces the deprecated stars.add/stars.remove APIs.

Note: This tool requires browser session tokens (xoxc/xoxd). It is not available with standard OAuth (xoxp) or bot (xoxb) tokens.

• Parameters:
  • item_id (string, required): Channel/DM ID where the saved message lives (from saved_list output).
  • ts (string, required): Message timestamp of the saved item (from saved_list output).
  • mark (string, optional): Set to "completed" to mark the item as done.
  • date_due (number, optional): Unix timestamp for due date/reminder. Set to 0 to clear.

18. saved_clear_completed

Clear all completed saved items from the "Save for Later" panel. This is a bulk operation that removes all items with state="completed".

Note: This tool requires browser session tokens (xoxc/xoxd). It is not available with standard OAuth (xoxp) or bot (xoxb) tokens.

• Parameters: None.

Resources

The Slack MCP Server exposes two special directory resources for easy access to workspace metadata:

1. slack://<workspace>/channels — Directory of Channels

Fetches a CSV directory of all channels in the workspace, including public channels, private channels, DMs, and group DMs.

• URI: slack://<workspace>/channels
• Format: text/csv
• Fields:
  • id: Channel ID (e.g., C1234567890)
  • name: Channel name (e.g., #general, @username_dm)
  • topic: Channel topic (if any)
  • purpose: Channel purpose/description
  • memberCount: Number of members in the channel

2. slack://<workspace>/users — Directory of Users

Fetches a CSV directory of all users in the workspace.

• URI: slack://<workspace>/users
• Format: text/csv
• Fields:
  • userID: User ID (e.g., U1234567890)
  • userName: Slack username (e.g., john)
  • realName: User’s real name (e.g., John Doe)

Setup Guide

• Authentication Setup
• Installation
• Configuration and Usage

Environment Variables (Quick Reference)

Variable	Required?	Default	Description
SLACK_MCP_XOXC_TOKEN	Yes*	nil	Slack browser token (xoxc-...)
SLACK_MCP_XOXD_TOKEN	Yes*	nil	Slack browser cookie d (xoxd-...)
SLACK_MCP_XOXP_TOKEN	Yes*	nil	User OAuth token (xoxp-...) — alternative to xoxc/xoxd
SLACK_MCP_XOXB_TOKEN	Yes*	nil	Bot token (xoxb-...) — alternative to xoxp/xoxc/xoxd. Bot has limited access (invited channels only, no search)
SLACK_MCP_PORT	No	13080	Port for the MCP server to listen on
SLACK_MCP_HOST	No	127.0.0.1	Host for the MCP server to listen on
SLACK_MCP_API_KEY	No	nil	Bearer token for SSE and HTTP transports
SLACK_MCP_PROXY	No	nil	Proxy URL for outgoing requests
SLACK_MCP_USER_AGENT	No	nil	Custom User-Agent (for Enterprise Slack environments)
SLACK_MCP_CUSTOM_TLS	No	nil	Send custom TLS-handshake to Slack servers based on SLACK_MCP_USER_AGENT or default User-Agent. (for Enterprise Slack environments)
SLACK_MCP_SERVER_CA	No	nil	Path to CA certificate
SLACK_MCP_SERVER_CA_TOOLKIT	No	nil	Inject HTTPToolkit CA certificate to root trust-store for MitM debugging
SLACK_MCP_SERVER_CA_INSECURE	No	false	Trust all insecure requests (NOT RECOMMENDED)
SLACK_MCP_ADD_MESSAGE_TOOL	No	nil	Enable message posting via conversations_add_message by setting it to true for all channels, a comma-separated list of channel IDs to whitelist specific channels, or use ! before a channel ID to allow all except specified ones. If empty, the tool is only registered when explicitly listed in SLACK_MCP_ENABLED_TOOLS.
SLACK_MCP_ADD_MESSAGE_MARK	No	nil	When conversations_add_message is enabled (via SLACK_MCP_ADD_MESSAGE_TOOL or SLACK_MCP_ENABLED_TOOLS), setting this to true will automatically mark sent messages as read.
SLACK_MCP_ADD_MESSAGE_UNFURLING	No	nil	Enable to let Slack unfurl posted links or set comma-separated list of domains e.g. github.com,slack.com to whitelist unfurling only for them. If text contains whitelisted and unknown domain unfurling will be disabled for security reasons.
SLACK_MCP_REACTION_TOOL	No	nil	Enable reactions_add and reactions_remove tools by setting to true for all channels, a comma-separated list of channel IDs to whitelist specific channels, or use ! before a channel ID to allow all except specified ones. If empty, the tools are only registered when explicitly listed in SLACK_MCP_ENABLED_TOOLS.
SLACK_MCP_ATTACHMENT_TOOL	No	nil	Enable the attachment_get_data tool by setting to true, 1, or yes. Does not support channel-level restrictions. If empty, the tool is only registered when explicitly listed in SLACK_MCP_ENABLED_TOOLS.
SLACK_MCP_MARK_TOOL	No	nil	Enable the conversations_mark tool by setting to true or 1. Disabled by default to prevent accidental marking of messages as read.
SLACK_MCP_USERS_CACHE	No	~/Library/Caches/slack-mcp-server/users_cache.json (macOS) ~/.cache/slack-mcp-server/users_cache.json (Linux) %LocalAppData%/slack-mcp-server/users_cache.json (Windows)	Path to the users cache file. Used to cache Slack user information to avoid repeated API calls on startup.
SLACK_MCP_CHANNELS_CACHE	No	~/Library/Caches/slack-mcp-server/channels_cache_v2.json (macOS) ~/.cache/slack-mcp-server/channels_cache_v2.json (Linux) %LocalAppData%/slack-mcp-server/channels_cache_v2.json (Windows)	Path to the channels cache file. Used to cache Slack channel information to avoid repeated API calls on startup.
SLACK_MCP_LOG_LEVEL	No	info	Log-level for stdout or stderr. Valid values are: debug, info, warn, error, panic and fatal
SLACK_MCP_GOVSLACK	No	nil	Set to true to enable GovSlack mode. Routes API calls to slack-gov.com endpoints instead of slack.com for FedRAMP-compliant government workspaces.
SLACK_MCP_ENABLED_TOOLS	No	nil	Comma-separated list of tools to register. If empty, all read-only tools and usergroups tools are registered; write tools (conversations_add_message, reactions_add, reactions_remove, attachment_get_data) require their specific env var OR must be explicitly listed here. When a write tool is listed here, it's enabled without channel restrictions. Available tools: conversations_history, conversations_replies, conversations_add_message, reactions_add, reactions_remove, attachment_get_data, conversations_search_messages, channels_list, usergroups_list, usergroups_me, usergroups_create, usergroups_update, usergroups_users_update.

*You need one of: xoxp (user), xoxb (bot), or both xoxc/xoxd tokens for authentication.

Limitations matrix & Cache

Users Cache	Channels Cache	Limitations
:x:	:x:	No cache, No LLM context enhancement with user data, tool channels_list will be fully not functional. Tools conversations_* will have limited capabilities and you won't be able to search messages by @userHandle or #channel-name, getting messages by @userHandle or #channel-name won't be available either.
:white_check_mark:	:x:	No channels cache, tool channels_list will be fully not functional. Tools conversations_* will have limited capabilities and you won't be able to search messages by @userHandle or #channel-name, getting messages by @userHandle or #channel-name won't be available either.
:white_check_mark:	:white_check_mark:	No limitations, fully functional Slack MCP Server.

Debugging Tools

# Run the inspector with stdio transport
npx @modelcontextprotocol/inspector go run mcp/mcp-server.go --transport stdio

# View logs
tail -n 20 -f ~/Library/Logs/Claude/mcp*.log

Security

• Never share API tokens
• Keep .env files secure and private

License

Licensed under MIT - see LICENSE file. This is not an official Slack product.