phone_validate

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

No annotations are provided, so the description carries the full burden, and it does so well: it discloses the exact cost ($0.0045 USDC per call) and p99 latency (50ms), plus enumerates return fields and line_type values. It stops short of describing error/failure behavior or auth requirements, keeping it below 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?

A single dense paragraph that is well front-loaded: purpose first, then return shape, then the country_code hint, then cost/latency. Every clause earns its place, though the return-field enumeration is somewhat lengthy for a short description.

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 annotations and no output schema, the description compensates by explaining the return fields (is_valid, e164, national_format, country_code, line_type), cost, and latency. It is nearly complete for a simple validation tool; only error-case behavior is unaddressed.

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 fully documented in the schema, making 3 the baseline. The description's country_code hint ('for local numbers without country prefix') largely restates the schema wording rather than adding new syntax or format detail.

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?

States a specific verb ('parse and validate') and resource ('any phone number worldwide'), and names the underlying engine (libphonenumber). An agent can distinguish it at a glance from the many other validation siblings (email_validate, vat_validate, iban_validate) since it is unambiguously phone-specific.

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?

Gives a clear conditional instruction: 'Provide country_code hint (e.g. DE) for local numbers without country prefix,' which tells the agent when the optional parameter matters. It lacks explicit when-to-use/when-not-to-use framing versus alternatives, but no competing phone tool exists among the siblings, so the gap is minor.

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