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

Adds substantial behavior beyond the annotations: live RDAP lookup, exact status values, registry_status and expires_at behavior, deletion states, unknown reasons, and hourly rate-limit cost per name. It also clarifies that the tool is observation-only and does not register, store, or publish anything.

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?

Front-loaded with the core use case and the batching rule, then proceeds through status semantics and caveats. It is dense but mostly earns its length; a few clauses could be tightened without losing safety-critical meaning.

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?

Complete for this tool's complexity: the output schema can carry return details, while the description covers the safety-critical interpretation of statuses and the operational cost of each name. No important invocation or interpretation gap is left for the agent.

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?

The schema already documents the names array thoroughly, including count limits and punycode normalization. The description still adds useful invocation semantics by emphasizing a single batch call and noting that each name counts against the hourly limit.

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 candidate domain names for existing registrations. It is clearly distinguishable from siblings such as lookup_registration because it is scoped to bulk candidate-name selection and registration status.

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?

Explicitly says when to use it: while the user is choosing a domain name and wants to know which candidates are registered. It also gives hard usage rules, including batching up to 20 names in one call and never treating 'not_registered' as broadly 'available'.

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