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

Annotations already declare readOnly, idempotent, open-world, non-destructive, so the safety profile is covered. The description adds two things annotations cannot: the per-call cost ($0.25 USDC via x402) and the concrete return payload. It does not describe failure behavior for invalid numbers or whether partial results are returned, which keeps it below 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?

Three compact sentences, front-loaded with the core purpose and output fields, then use cases, then cost. The field enumeration is long but justified because no output schema exists. 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?

With no output schema, the description carries the return-value burden and does so thoroughly, plus adds the billing model. The only gap is error/invalid-input behavior and any rate consideration for a paid endpoint.

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 coverage is 100% and both parameters are documented in-schema (including the enum list and the note that language does not change price). The description adds nothing about accepted phone formats or default region handling, so the baseline 3 applies.

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?

"Phone number intelligence: validates a phone number and returns its normalized international form, country, region, line type, carrier, organization, time zone, and risk assessment" is a specific verb+resource with an enumerated output. That clearly distinguishes it from the nearest sibling interzoid_ip_profile (IP-based geolocation) and the email tools, which cover related but 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?

It lists target scenarios (fraud prevention, contact data verification, lead qualification, call routing), which implies when to call it. But there is no exclusion or alternative routing — nothing says what to do for email/IP/address lookups or when a cheaper sibling would suffice.

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