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

With no annotations provided, the description does the work of disclosing behavior: it is a read-only, non-probing validation, and the explicit 'no SMTP check' line rules out the most likely false expectation. It also enumerates the outputs (flags, typo suggestion, risk score), which substitutes for a missing output schema. Rate limits, cost, or latency are unmentioned, but this is a substantial disclosure for an unannotated tool.

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?

Two sentences, no filler: the capability list comes first and the limitation follows as a tight qualifier. The feature enumeration is dense but every item is a distinct output an agent needs to know about.

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?

For a one-parameter read-only validator with no annotations and no output schema, the description covers what is checked, what is not checked, and what kinds of values come back. It does not describe the response shape in detail (e.g., field names or error behavior for malformed input), which keeps it short of a 5.

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 required parameter with 100% schema description coverage including an example, so the schema already carries the parameter burden. The description adds only the 'domain level' framing, which is more about scope than about the input format. Baseline 3 is appropriate when the schema does the heavy lifting.

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 names a specific verb (validate) and resource (email address) and enumerates exactly what is checked — syntax, domain/MX health, disposable-domain and role-account flags, typo suggestion, and a 0-100 risk score. That enumeration also implicitly separates it from siblings like validate_card or validate_vat, which act on entirely different identifiers.

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 gives a clear positive context (domain-level email validation) plus one explicit exclusion: it does not probe whether the mailbox exists and performs no SMTP check. This is an important boundary because an agent might otherwise expect deliverability verification. It stops short of naming alternatives or stating prerequisites, so it is strong but not exhaustive.

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