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

Annotations already declare a safe read-only, idempotent, open-world call, and the description adds real context beyond them: the no-website-fetch guarantee, the credit cost model (1 credit per registry-answered name, free for invalid/duplicate/unanswered), and the API-key requirement. These are exactly the operational facts an agent needs before invoking at scale.

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 short blocks: what it does, the routing advice, then the return values and cost. Purpose is front-loaded, and every sentence earns its place with no repetition of structured fields.

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?

Even though an output schema exists, the description summarizes the four possible statuses and why one appears, plus auth and billing prerequisites. Combined with the annotations and the 500-name limit, an agent has 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?

Schema description coverage is 0%, so the description must carry the parameter burden. It usefully adds the 'up to 500 domain names' cap for the names array and mentions DNS/registry sources, but the boolean `dns` parameter — its default of true and what toggling it changes — is never explained.

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 and resource — screening a list of domains for registrability — and explicitly scopes the check to registry RDAP records and DNS, plus a clarifying negative ('Nothing is fetched from the names' websites'). It is clearly distinguishable from the sibling domainReport, which it names as the follow-up rather than a substitute.

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 explicit when-to-use ('cut a long list of candidate or dropping names down to a shortlist') and names the alternative for the next step ('then run domainReport on the few that matter'), so the agent knows both the trigger and the routing.

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