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

Annotations are all false and do not describe the safety/side-effect profile, so the description carries the burden. It adds meaningful behavior: GET returns inbox and POST sends, empty inbox is acceptable, peer mail bodies are marked content_trust: untrusted_peer_content, and DIDs are not keys. It does not mention failure modes or recipient validation, but the disclosed caveats go well beyond the structured data.

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?

The description is compact and front-loaded with the resource and operation. Each following sentence adds a distinct caveat (authentication, empty inbox, sibling restriction, content trust). The phrase 'proven' and the abrupt DID/key statement are slightly cryptic, but the structure is efficient.

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?

With an output schema present, return-value documentation is not needed. The description explains the main operations and important security caveats. It still leaves gaps such as what 'proven' means, whether to is a DID or peer identifier, and how send failures or invalid recipients are handled, which matters for a POST tool with no required parameters.

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 covers 67% of parameters with rich descriptions for nonce, leave_token, controller_signature, and controller_public_key. The description itself does not explain to or body, which are undocumented in the schema, though 'POST send' makes their roles broadly inferable. It adds no extra parameter meaning and only partially compensates for the missing descriptions.

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 first sentence names specific operations and resource ('GET /api/message inbox (proven) or POST send'), so the agent knows this tool reads and writes mail. It also differentiates from a sibling by noting 'Look cannot write mail.' The cryptic 'proven' and the DID/key caveat add ambiguity, keeping it from a 5.

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 context for when to use GET vs POST mode and explicitly says Look cannot write mail, which implies message is the mail-writing tool. It does not, however, give clear when-to/when-not-to guidance against other sibling messaging or posting tools such as plaza_post or peers, so route selection is mostly left to inference.

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