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

Annotations cover only the safety profile (not read-only, non-destructive, open-world), while the description adds substantive behaviour: 24-hour expiry, receive-only, valid only while it exists, and a rate limit of 20 inboxes per hour per IP. That is exactly the context annotations cannot express.

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 purpose and return values are front-loaded, and every clause carries information. Slightly dense with four separate operational facts packed in, but nothing is redundant with the schema or annotations.

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 no output schema, the description still describes what is returned (an address and an inbox_token) and how to consume it. Combined with the lifecycle and rate-limit details, an agent has everything needed to call and use this tool correctly.

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% and the single optional 'review' parameter is fully documented in the schema, so the baseline of 3 applies. The description adds no extra meaning about the parameter, but none is needed.

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?

States a specific verb and resource ('Create a temporary email inbox') and immediately narrows scope to testing signup or email flows for products the user owns or may test. It also names the sibling check_inbox as the reader tool, so an agent can distinguish it from siblings without opening a schema.

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?

Gives a clear use context (testing the signup/email flow of an owned or authorised product, within terms) and routes reading to check_inbox. It stops short of explicit when-not-to-use guidance or naming other alternatives among the eleven siblings.

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