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

With no annotations, the description carries the full behavioral burden. It usefully discloses that the workspace/server must already be connected by the owner and that Markdown is supported, but says nothing about failure modes (unknown channel, missing connection), permissions, rate limits, or whether posts are editable/deletable.

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

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

One compact paragraph with the core action front-loaded, followed by the reply exclusion and the `where` hint. The aside "or where it fits" is slightly loose but the whole thing stays tight.

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

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

There is no output schema or annotation coverage, so the description must stand alone; it covers target platform, addressing, message format, and the new-vs-reply distinction. Only error and permission behavior are absent, which is a modest gap for a simple send operation.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema description coverage is 100%, so the schema already documents `channel`, `text`, and `where` with examples and the uniqueness rule. The description restates the `where` disambiguation hint without adding syntax or format detail beyond what the schema provides, so the baseline 3 applies.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Does the description clearly state what the tool does and how it differs from similar tools?

The description names a specific verb and resource ("Post a message into a Slack or Discord channel") and clarifies the message type is a new post, not a reply. It does not differentiate itself from the closest sibling, mail_send, so an agent choosing between messaging surfaces gets no explicit routing help.

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

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

It gives positive context ("where they asked reports to go, or where it fits") and an explicit exclusion ("A new message, not a reply: to answer someone, just answer in the conversation"). No named alternatives are offered, but the when/when-not split is clear enough to act on.

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