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

Annotations already cover the safety profile (readOnly, idempotent, non-destructive, open-world), but the description adds useful behavioral detail beyond them: no email is sent, MX/A lookup is null-MX aware, disposable-domain coverage is roughly 10k domains, typo correction is included, and pricing is $0.005 USDC per successful call via x402 on Solana. It does not cover rate limits or failure-charging semantics, so it falls short of a 5.

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 definition is front-loaded with the core purpose and immediately follows with the checks performed, then pricing and the HTTPS alternative. Every clause carries useful information, and there is 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?

Given that there is no output schema, the description does a good job listing the checks and the overall verdict. It is nearly complete for calling the tool, but it does not describe the shape of the verdict or how the individual flags are returned.

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 both parameters are already well documented in the schema. The description mentions MX/A lookup and the overall check suite, but it does not add parameter-specific semantics beyond what the schema already says.

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 gives a specific verb and resource (validate an email address) and enumerates the exact checks performed, including syntax, MX/A lookup, disposable-domain detection, role/free-provider flags, typo suggestion, and verdict. This scope distinguishes it from narrower sibling tools like mx_check and email_auth by making clear it is a comprehensive validator.

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 phrase 'without sending mail' gives implicit usage context, and the checks listed imply when the tool is appropriate. However, it does not explicitly say when to use this instead of siblings such as mx_check or email_auth, nor does it state exclusions or prerequisites.

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