Check one email address

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

Annotations only declare readOnlyHint and openWorldHint, so the description carries the substantive behavioral load and does it well: it explains what each status means, that an 'unconfirmed' result means the mailbox itself was not verified, and how did_you_mean is populated. It stops short of noting rate limits, quota, or whether the check is real-time, but the core semantics are unusually well disclosed.

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, each carrying distinct load: what is checked, what each status means, and what did_you_mean contains. The most important content (the checked categories) is front-loaded with no filler.

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 correctly compensates by documenting the return fields (status values and did_you_mean) and the meaning of the 'unconfirmed' outcome. Nothing an agent needs in order to call and interpret this tool is missing.

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?

There is a single parameter at 100% schema description coverage, so the schema already documents it fully. The description adds no format, normalization, or trimming detail beyond the schema, which puts it at the baseline for fully covered parameters.

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 opens with a specific verb and resource ('Check one email address') and enumerates exactly what is validated (syntax, domain typos, disposable domains, role addresses, non-existent domains). The singular 'one' implicitly separates it from the sibling check_emails, so an agent can pick correctly 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?

It defines the validation use case clearly and the three status outcomes give the agent a sense of when each result type applies. However, it never explicitly names the alternative sibling check_emails or states when to prefer it, so the routing guidance stays implicit rather than stated.

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