Verify an email address

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

Annotations already declare readOnlyHint=false, openWorldHint=true and idempotentHint=false, and the description adds the reason behind the non-idempotency: every repeated check of the same address is charged again, and unknown results are free. That credit accounting is exactly the kind of context annotations cannot express. It does not cover latency, SMTP timeout behavior, or auth requirements, which a live SMTP probe would plausibly have.

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 tight sentences: purpose first, then the return payload, then billing. The dense field enumeration earns its length because there is no output schema, and nothing is repeated from 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 correctly substitutes by enumerating status values and flags, and it explains the credit model. The one meaningful gap is operational: a live SMTP/MX check is slow and can time out, and nothing tells the agent what to expect or how errors surface.

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?

One required parameter at 100% schema description coverage, so the schema already fully documents `email`. The description adds no format, normalization, or casing guidance beyond it, which is the expected baseline when the schema carries the burden.

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?

Opens with a specific verb+resource ("Verify a single email address") and the word "single" implicitly marks the boundary against the sibling verify_emails_bulk. The return-field list further pins down what the tool produces. It stops short of naming the bulk sibling explicitly, so the differentiation is inferred rather than stated.

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?

"Single email address" hints that bulk verification belongs to verify_emails_bulk, but no sentence says when to use this versus that tool. Prerequisites, batch alternatives, and failure contexts are left to inference.

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