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Claude Code ⇄ Slack

Claude Code ⇄ Slack

by Palgenius
OverviewSchemaSourceRelated ServersDiscussionsAdmin
TypeScript
Local

send_slack_message

Post a reply to a Slack channel or thread and get back a timestamp, so the same message can later be updated in place instead of reposting.

Instructions

Send a message to a Slack channel. Use this to reply to webhook channel incoming messages from Slack. Returns the message timestamp (ts) — pass it to update_slack_message to rewrite this message later, which is how a progress or "working on it" marker is kept to one line instead of many.

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>",
      "text": "<text>"
    },
    "name": "send_slack_message"
  }
}

Input Schema

NameRequiredDescriptionDefault
textYesThe reply, written as ordinary markdown. It is converted to Slack formatting for you — write **bold**, `code`, fenced blocks and [links](url) normally. A message over Slack's length limit is split across several posts rather than truncated.
channelYesThe Slack channel ID to send the message to (e.g. C0AMZUV0JTZ)
thread_tsNoReply inside a thread. Pass the thread_ts from the incoming message so the answer sits under the question instead of at the top of the channel. Omit only when starting a new topic.

Schema Changelog

Changes observed during successful MCP inspections.

  1. First observedv2.0.0

TDQS

A4.1/5.0
Behavior4/5

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

With no annotations, the description carries the full burden, and it delivers key behavior: it returns the message timestamp (ts) and explains the chaining pattern with update_slack_message for keeping a progress marker to one line. It omits permissions/auth needs, rate limits, and failure behavior, so it is substantive but not complete.

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?

Two sentences, front-loaded with the core action and the return-value/chaining contract. The second sentence is somewhat dense with a nested clause about the progress marker, but every part earns its place.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Completeness4/5

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

There is no output schema, so the description correctly fills the gap by naming the return value (ts) and its use. Combined with 100% schema coverage on inputs, an agent has nearly everything needed; only auth/error context is missing.

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%, so channel, text, and thread_ts are already fully documented in the schema, including markdown conversion and length-splitting. The description adds no parameter-level detail beyond that, so baseline 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?

States a specific verb+resource ('Send a message to a Slack channel') and further scopes it to replying to incoming webhook channel messages. It implicitly separates itself from update_slack_message (rewrite) and send_slack_image (images) by naming the former as the follow-up step.

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

Usage Guidelines4/5

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

Gives a clear use case ('reply to webhook channel incoming messages from Slack') and points to update_slack_message for later rewriting. It stops short of explicitly stating when NOT to use this tool (e.g., use send_slack_image for images, update_slack_message for edits), so the agent must infer the alternatives from sibling names.

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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