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

Goes well beyond the annotations by disclosing that no API key is required, that the batch cap is 50, and that batching reduces rate-limit hits — genuine operational context the readOnly/openWorld hints do not convey. It stops short of describing failure behavior for invalid or partial batches, keeping it out of the top band.

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 tight sentences, front-loaded with the key differentiators (public, no key, batch of 50) and ending on the decision rule. Every sentence earns its place with 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-shape burden itself by enumerating availability, price, renewal price, registrar, and buyUrl. Combined with the cost/auth and rate-limit context, an agent has everything needed to call and use the result.

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 the single parameter already documents its array-of-FQDNs format plus a concrete example. The description's 'up to 50 domains' restates the schema's maxItems rather than adding new syntax or constraint detail, 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?

States a specific verb and resource ('checks up to 50 domains in ONE call') and explicitly positions itself against the sibling check_domain_public. An agent can distinguish it from check_domain and check_domain_public without opening any 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?

Contains an explicit routing rule: 'ALWAYS prefer this over multiple check_domain_public calls when you have more than one candidate.' That names the alternative and the exact condition that selects it, leaving nothing to inference.

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