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 behavioral traits: it runs the same checks as send_email, does not send an email, and does not consume quota. This reassures the agent that it is a non-mutating preflight, though it does not explicitly state all side-effect-free behavior or auth requirements.

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: first states the core function, second gives usage context, third provides the endpoint. No fluff or redundancy, and key information is front-loaded.

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?

The description provides good usage context but does not explain what the check returns or how to interpret the result, especially since there is no output schema. Additionally, the API endpoint's address concept is not reconciled with the domain/slug parameters, leaving a minor gap for an agent trying to 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?

Schema description coverage is 100%, so the baseline is 3. The description does not add meaning beyond the schema; the API path uses an '{address}' placeholder while the schema requires separate 'domain' and 'slug' fields, which could cause slight confusion but does not break understanding since the schema descriptions are clear.

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 tool's function: running the same deliverability and abuse-safety checks as send_email, but without sending or consuming quota. This specific verb+resource+scope distinguishes it from the sibling send_email tool and other email-related 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?

It gives explicit guidance on when to use: 'before authentication, payment, onboarding, or high-volume messages.' It also implies when not to use (when you want to actually send) by noting it does not send. However, it does not explicitly name alternative tools or provide exclusion scenarios.

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