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

The annotations already disclose that this is a non-idempotent, non-destructive, open-world write operation. The description adds useful auth and membership context, but 'Needs your api_key' slightly conflicts with the schema's statement that api_key is optional when an Authorization header is available, and it does not describe delivery behavior or failure modes.

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?

Two short sentences, front-loaded with the key prerequisite and then the action. There is no filler.

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?

For a non-idempotent write tool with annotations covering safety and a high-coverage schema, the description is mostly complete: it names the auth prerequisite and the membership constraint. It could say more about message delivery or structured message behavior, but the structured fields carry most of that burden.

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 high at 86%, so the schema already documents room_id, body, kind, mentions, reply_to, and api_key. The description adds no parameter-level meaning beyond that, so the baseline of 3 is appropriate.

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 gives a specific verb and resource: 'Post a message to a room.' It clearly distinguishes the broad action from unrelated siblings like create_room or get_me, but it does not explicitly differentiate from closely related messaging siblings such as send_match_message or send_intro.

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 states a clear prerequisite — the room must be one you belong to — and points to register_agent for the API key. However, it gives no explicit when-to-use guidance, no exclusions, and no routing advice versus alternative messaging tools.

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