Slack MCP Server

Instructions

Implementation Reference

• src/tools.ts:185-228 (handler)

  The handler function that executes the conversations_replies tool. Validates input, resolves channel ID, calls Slack conversations.replies API, filters messages, and returns formatted response.

  export async function conversationsReplies(args: any): Promise<ToolResponse> {
    try {
      const validated = ConversationsRepliesSchema.parse(args);
      const client = new WebClient(validated.accessToken);
  
      console.log('Fetching thread replies for channel:', validated.channel_id, 'thread:', validated.thread_ts);
  
      // Resolve channel name/username to ID if needed
      const channelId = await resolveChannelId(client, validated.channel_id);
  
      // Parse limit parameter
      const limitParams = parseLimit(validated.limit);
  
      // Fetch thread replies
      const result = await client.conversations.replies({
        channel: channelId,
        ts: validated.thread_ts,
        cursor: validated.cursor,
        ...limitParams
      });
  
      // Filter out activity messages if not requested
      let messages = result.messages || [];
      if (!validated.include_activity_messages) {
        messages = messages.filter((msg: any) => !msg.subtype || !['channel_join', 'channel_leave'].includes(msg.subtype));
      }
  
      return {
        success: true,
        data: {
          messages,
          has_more: result.has_more,
          cursor: result.response_metadata?.next_cursor,
          channel_id: channelId,
          thread_ts: validated.thread_ts
        }
      };
    } catch (error: any) {
      if (error.name === 'ZodError') {
        return { success: false, error: `Validation error: ${error.errors.map((e: any) => e.message).join(', ')}` };
      }
      return handleSlackError(error);
    }
  }

• src/schemas.ts:19-26 (schema)

  Zod schema defining the input parameters and validation for the conversations_replies tool.

  export const ConversationsRepliesSchema = z.object({
    accessToken: z.string().describe("Slack OAuth token (xoxp-... or xoxb-...)"),
    channel_id: z.string().describe("Channel ID (e.g., C1234567890), channel name (#general), or DM (@username)"),
    thread_ts: z.string().describe("Message timestamp in format 1234567890.123456"),
    limit: z.union([z.string(), z.number()]).optional().describe("Time range (1d, 7d, 1m, 90d) or message count (e.g., 100)"),
    cursor: z.string().optional().describe("Pagination cursor from previous response"),
    include_activity_messages: z.boolean().optional().describe("Include join/leave system messages (default: false)")
  });

• src/index.ts:100-104 (registration)

  Registers the conversations_replies tool in the MCP server's tool list, providing name, description, and input schema.

  {
    name: 'conversations_replies',
    description: 'Fetches all messages in a specific thread by channel and thread timestamp. Supports pagination.',
    inputSchema: zodToMCPSchema(ConversationsRepliesSchema)
  },

• src/index.ts:133-135 (registration)

  Dispatches execution of the conversations_replies tool in the server's callTool handler switch statement.

  case 'conversations_replies':
    result = await conversationsReplies(args);
    break;