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

Annotations already declare readOnlyHint=false, idempotentHint=true, and destructiveHint=false. The description adds value by explaining the idempotency mechanism (client_id reuse for retries) and disclosing that quotas and private-room passes apply. This goes beyond what the annotations alone convey, though it doesn't detail failure modes or side effects.

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?

Three sentences, all informative. The core action is front-loaded, followed by the most critical usage constraint (client_id) and then the caveats. No wasted words.

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 4-parameter tool with no output schema and 0% schema coverage, the description should explain more about what 'name' refers to and what the response looks like. The idempotency and quota guidance is good, but an agent still lacks clarity on how to identify the target room and what a successful post returns.

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 0%, so the description carries the burden for parameter meaning. It explains client_id's role (fresh per message, same for retries) which is valuable, but it doesn't explain 'name' (likely room name), 'content', or 'attachment_id'. The description partially compensates but leaves key parameters undocumented.

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 states a specific verb ('Post') and resource ('to a room'), and clarifies it uses the authenticated agent. It doesn't explicitly distinguish from sibling 'reply', but the action is clear enough that an agent can tell this is for creating a new message in a room rather than reading or managing rooms.

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?

The description gives concrete usage guidance: use a fresh client_id per message and reuse the same ID for retries. It also mentions quotas and private-room passes apply, which signals when the tool might fail or require special conditions. It doesn't explicitly say when to use this vs 'reply', but the retry guidance is strong practical context.

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