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slack-mcp-server

slack-mcp-server

by dudztroyer
OverviewSchemaSourceRelated ServersDiscussionsAdmin
JavaScript
Remote

Reply to Slack Thread

slack_reply_to_thread

Reply to a specific message thread in Slack. Specify the channel, the parent message's timestamp, and the reply text.

Instructions

Reply to a specific message thread in Slack. Accepts both channel names (#general, general) and channel IDs (C1234567890).

Tool call template

Replace each placeholder with a value matching the input schema. Only required parameters are included; add optional parameters as needed.

{
  "id": 1,
  "jsonrpc": "2.0",
  "method": "tools/call",
  "params": {
    "arguments": {
      "channel": "<channel>",
      "thread_ts": "<thread_ts>",
      "text": "<text>"
    },
    "name": "slack_reply_to_thread"
  }
}

Input Schema

NameRequiredDescriptionDefault
channelYesThe channel name (e.g., #general, general) or channel ID (e.g., C1234567890) 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

Schema Changelog

Changes observed during successful MCP inspections.

  1. First observedv0.0.5

TDQS

C2.9/5.0
Behavior2/5

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

With no annotations provided, the description bears full responsibility for behavioral disclosure. It explains the input (reply to a thread) but does not describe side effects (e.g., that the reply is appended to the thread, permissions required, or rate limits). For a mutation tool, this is insufficient for the agent to understand the impact.

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?

The description consists of two concise sentences covering purpose and a key detail about channel formats. It is front-loaded and contains no unnecessary words. However, it could be slightly more informative without becoming verbose (e.g., mentioning plain text vs markdown).

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 tool's simplicity (3 required params, no output schema), the description is mostly adequate but missing context about the return value (likely the message object), error cases (e.g., invalid thread_ts), or that it requires write permissions. For a well-understood action like replying to a thread, this may be sufficient, but additional context would improve completeness.

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 coverage is 100%, so the baseline is 3. The description adds no new information beyond the schema's parameter descriptions; it repeats the channel format flexibility already documented. No additional meaning or context is provided for the thread_ts or text parameters.

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 it replies to a Slack thread, specifying the resource (thread) and the action (reply). It distinguishes from siblings like slack_post_message (which sends a new message, not a reply) and slack_get_thread_replies (read-only). However, it does not differentiate from slack_reply_to_thread_markdown, which may be a markdown variant, so the purpose is slightly ambiguous regarding markdown support.

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?

The description provides no guidance on when to use this tool versus alternative sibling tools such as slack_reply_to_thread_markdown or slack_post_message. It only mentions channel name/ID acceptance, which is a parameter detail rather than usage context. Without exclusions or when-not-to-use guidance, the agent lacks decision support.

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

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