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z9905080

MCP Server for Slack

by z9905080

slack_reply_to_thread

Post replies to specific message threads in Slack channels using channel ID, thread timestamp, and reply text.

Instructions

Reply to a specific message thread in Slack

Input Schema

TableJSON Schema
NameRequiredDescriptionDefault
channel_idYesThe ID of the channel containing the thread
thread_tsYesThe 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.
textYesThe reply text

Implementation Reference

  • Executes the slack_reply_to_thread tool by validating input arguments and invoking the SlackClient.postReply method to send the reply via Slack API.
    case "slack_reply_to_thread": {
      const args = request.params
        .arguments as unknown as ReplyToThreadArgs;
      if (!args.channel_id || !args.thread_ts || !args.text) {
        throw new Error(
          "Missing required arguments: channel_id, thread_ts, and text",
        );
      }
      const response = await slackClient.postReply(
        args.channel_id,
        args.thread_ts,
        args.text,
      );
      return {
        content: [{ type: "text", text: JSON.stringify(response) }],
      };
    }
  • Defines the Tool object for slack_reply_to_thread, including name, description, and input schema with required parameters: channel_id, thread_ts, text.
    const replyToThreadTool: Tool = {
      name: "slack_reply_to_thread",
      description: "Reply to a specific message thread in Slack",
      inputSchema: {
        type: "object",
        properties: {
          channel_id: {
            type: "string",
            description: "The ID of the channel containing the thread",
          },
          thread_ts: {
            type: "string",
            description: "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.",
          },
          text: {
            type: "string",
            description: "The reply text",
          },
        },
        required: ["channel_id", "thread_ts", "text"],
      },
    };
  • SlackClient method that makes the HTTP POST request to Slack's chat.postMessage API to reply to a thread, using the provided channel_id, thread_ts, and text.
    async postReply(
      channel_id: string,
      thread_ts: string,
      text: string,
    ): Promise<any> {
      const response = await fetch("https://slack.com/api/chat.postMessage", {
        method: "POST",
        headers: this.botHeaders,
        body: JSON.stringify({
          channel: channel_id,
          thread_ts: thread_ts,
          text: text,
        }),
      });
    
      return response.json();
    }
  • index.ts:567-582 (registration)
    Registers the slack_reply_to_thread tool (as replyToThreadTool) in the list of available tools returned by the ListToolsRequest handler.
    server.setRequestHandler(ListToolsRequestSchema, async () => {
      console.log("Received ListToolsRequest");
      return {
        tools: [
          listChannelsTool,
          postMessageTool,
          replyToThreadTool,
          addReactionTool,
          getChannelHistoryTool,
          getThreadRepliesTool,
          getUsersTool,
          getUserProfileTool,
          lookupUserByEmailTool,
        ],
      };
    });
  • TypeScript interface defining the input arguments for the slack_reply_to_thread tool, used for type checking in the handler.
    interface ReplyToThreadArgs {
      channel_id: string;
      thread_ts: string;
      text: string;
    }

Schema Changelog

Changes observed during successful MCP inspections.

  1. First observed

TDQS

B3.2/5.0
Behavior2/5

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

With no annotations, the description carries full burden for behavioral disclosure. It only mentions the action 'reply' but does not disclose any traits like rate limits, formatting constraints, required permissions, or what happens on invalid thread_ts.

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

Conciseness4/5

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

Single sentence, no fluff. It is appropriately sized for a simple action, though could be more informative.

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 3 required params, no output schema, and no annotations, the description is adequate but lacks details on return value or error scenarios. It covers the basic purpose but leaves gaps.

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%; the description adds no additional meaning beyond what the schema already provides. Baseline score of 3 applies.

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 verb 'reply', the resource 'specific message thread', and the platform 'Slack'. It is specific and distinguishes from siblings like slack_post_message (for new messages) and slack_get_thread_replies (for reading).

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

Usage Guidelines2/5

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

No guidance on when to use this tool versus alternatives like slack_post_message. No mentions of prerequisites, best practices, or when not to use.

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