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

With no annotations, the description carries the full burden. It discloses key behaviors: alias delivery, no mailbox slot consumption, same-domain requirement, and the API endpoint. However, it does not state side effects, reversibility, required permissions, or error behavior, leaving some transparency gaps.

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, front-loaded with the primary action, followed by a practical use case and a constraint. Every sentence adds value with no redundancy or fluff.

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 additive tool with no output schema, the description provides purpose, use case, constraints, and API route. It lacks explicit return/error information, but the operation is straightforward and the existing mailbox prerequisite is implied. This is reasonably complete.

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?

Input schema covers all three parameters with clear descriptions and examples (100% coverage). The description's mention of alias formats and domain adds little beyond what the schema already provides, so the score stays at the baseline for high schema coverage.

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 clearly states the action ('Add an alias address'), the resource ('mailbox'), and the key distinguishing behavior ('delivers into an existing mailbox, without using a mailbox slot'). It also specifies a domain constraint, effectively differentiating it from create_mailbox and similar tools.

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 provides a concrete use case ('multiple public addresses... landing in one inbox') and a critical prerequisite ('must be on the same domain as the mailbox'). While it does not explicitly name alternatives, the 'without using a mailbox slot' phrasing and sibling tools like create_mailbox make the intended usage evident.

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