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

Annotations already declare the safety profile (readOnly, idempotent, non-destructive, open-world), so the bar is lower. The description adds genuinely useful context beyond them: the per-call price ($0.005) and a concrete sample input, which help the agent budget and format calls.

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?

Purpose is front-loaded in the first clause, followed by tightly packed pricing, sample, and return-value lists. Dense but each element earns its place; 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 compensates by enumerating the returned fields (created, age_days, age_years, newly_registered, expires, registrar, source). Combined with full schema coverage and annotations, an agent has nearly everything needed to call 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?

There is a single parameter and schema description coverage is 100%, so the schema already defines 'domain' fully. The description's sample payload corroborates the format but adds no new constraints, making the baseline 3 appropriate.

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 states a specific resource (a domain's age) plus the concrete outputs (registration date, age in days/years, newly-registered flag), so an agent knows exactly what it gets. It does not differentiate itself from closely-named siblings like domain_whois or domain_profile, which also touch registration data.

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?

Usage is only implied: noting that a newly-registered status is 'a common phishing signal' hints at when this check is valuable, but the description never says when to pick this over domain_whois or domain_profile, nor any exclusions.

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