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

With zero annotations the description carries the full burden. It helpfully discloses that the lookup is free and registry-sourced and interprets the new-registration flag as a fraud signal, but says nothing about failure modes (unregistered or invalid domains), rate limits, or whether results are cached — material gaps for a read-only external lookup.

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 waste. 'Free.' is front-loaded as the first thing an agent needs to know, followed by the returned field list and then the interpretation of the risk flags.

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?

There is no output schema, so the description correctly compensates by enumerating the returned fields and explaining what the flags mean. Only the absence of error/edge-case behavior and cost/rate context keeps it from being fully complete.

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 at 100% schema description coverage ('Domain, for example stripe.com'), so the schema already fully documents it. The description adds no constraint on format (apex vs subdomain, IDN, trailing dot), so 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?

The description names the exact resource (RDAP registration data for one domain) and enumerates the returned fields: registration date and age, expiry, registrar, status codes, nameservers, DNSSEC. That is specific enough to separate it from the DNS-oriented sibling inspect_domain_dns without opening either schema.

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 implied rather than stated: 'a strong spam and fraud signal' suggests due-diligence and abuse-triage scenarios, and 'about to expire' hints at renewal monitoring. But there is no explicit when-to-use/when-not, no prerequisites, and no named alternative among the ten siblings.

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