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

With no annotations provided, the description carries the full burden of behavioral disclosure. It adds meaningful context by mentioning the 'verification window' and the fact that it bypasses the forward_to mailbox, which implies a targeted, read-oriented behavior. However, it does not explicitly state that the operation is read-only, what data it returns, or any 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?

The description is a single sentence that is front-loaded with the core action and includes a helpful example. Every word earns its place, and there is no redundant or filler content.

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?

This is a simple, single-parameter tool with no output schema. The description explains what the tool does, the scope, and even a practical use case. It could be more explicit about the returned email content or count, but for the tool's complexity it is sufficiently complete for an agent to select and invoke it 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?

The schema has one parameter 'domain' with 100% coverage, describing it as 'Domain to filter on'. The description reinforces this by saying 'for a given domain' and gives a concrete example, but does not add substantial new meaning beyond the schema. Baseline 3 applies because the schema already documents the parameter adequately.

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 uses a specific verb ('List') and clearly defines the resource ('mails received in the verification window') and scope ('for a given domain'). The example about Apple's verification code makes the purpose immediately understandable and distinguishes it from sibling tools like get_domain_verification_status and read_inbox.

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 conveys when to use the tool: to retrieve verification emails for a domain, specifically to find codes without checking the forward_to mailbox. It provides a clear use case and an implicit alternative (checking the forward_to mailbox), though it does not explicitly name sibling tools or state when not to use it.

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