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

With no annotations, the description carries the full behavioral burden and usefully discloses that the key is returned once and that sending starts at zero credits while receiving is free. It omits important behavior such as duplicate agentId handling, auth requirements, idempotency, and the full response shape.

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 two short sentences with no wasted words, and the core action is front-loaded. The credit and payment caveats are compact and relevant.

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 simple registration tool with no output schema, the description covers the main action, one-time key delivery, and initial credit state. It still leaves gaps around parameter meanings, duplicate registration behavior, and authentication expectations.

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 must explain the two parameters, but it does not mention agentId or name at all. An agent gets no semantic guidance on the required identifier pattern, the optional name, or how they relate to the mailbox.

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 and resource: create an agent mailbox and receive its key. It is clearly distinct from the listed siblings, which focus on email, payment, and proposal operations, though it does not explicitly differentiate itself.

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 provides useful context that the mailbox starts with zero sending credits and receiving works without payment, implying this is the setup step before receiving mail. However, it does not explicitly say when to call it versus alternatives or whether it must be called before send_email.

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