Slack MCP Server

Instructions

Implementation Reference

• src/index.ts:219-236 (handler)

  Handler for slack_reply_to_thread: parses input with ReplyToThreadRequestSchema, posts message to Slack thread using slackClient.chat.postMessage, handles error and returns success response.

  case 'slack_reply_to_thread': {
    const args = ReplyToThreadRequestSchema.parse(
      request.params.arguments
    );
    const response = await slackClient.chat.postMessage({
      channel: args.channel_id,
      thread_ts: args.thread_ts,
      text: args.text,
    });
    if (!response.ok) {
      throw new Error(`Failed to reply to thread: ${response.error}`);
    }
    return {
      content: [
        { type: 'text', text: 'Reply sent to thread successfully' },
      ],
    };
  }

• src/schemas.ts:204-217 (schema)

  Zod input schema for slack_reply_to_thread tool defining channel_id (string), text (string), and thread_ts (string with regex validation for Slack timestamp format).

  export const ReplyToThreadRequestSchema = z.object({
    channel_id: z
      .string()
      .describe('The ID of the channel containing the thread'),
    text: z.string().describe('The reply text'),
    thread_ts: z
      .string()
      .regex(/^\d{10}\.\d{6}$/, {
        message: "Timestamp must be in the format '1234567890.123456'",
      })
      .describe(
        "The timestamp of the parent message in the format '1234567890.123456'. Timestamps in the format without the period can be converted by adding the period such that 6 numbers come after it."
      ),
  });

• src/index.ts:126-130 (registration)

  Tool registration in listTools response: defines name, description, and inputSchema for slack_reply_to_thread.

  {
    name: 'slack_reply_to_thread',
    description: 'Reply to a specific message thread in Slack',
    inputSchema: zodToJsonSchema(ReplyToThreadRequestSchema),
  },