check_domain

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

Given the readOnlyHint annotation, the description adds substantial behavioral context beyond it: real-time RDAP data, exact response shapes for both registered and unregistered domains, fields like status and dates, potential registrar redaction for privacy, and a clean error path for malformed input. No contradiction with annotations.

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?

The description is moderately long but every sentence earns its place: purpose, usage examples, parameter format, two possible successful responses, and error behavior are each covered. It is well-organized and front-loaded with the primary purpose, making it easy for an agent to scan.

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?

For a single-parameter tool with an output schema, the description effectively explains all relevant runtime behaviors: availability, registration details, field format (ISO 8601), status codes, privacy redaction, and error handling. The output schema existence is acknowledged indirectly through the described return structures, and nothing important seems omitted.

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?

With 0% schema description coverage, the description fully compensates by precisely defining the 'domain' parameter: 'a bare domain like "example.com" — no protocol prefix, no path, no spaces.' It also clarifies that malformed inputs trigger an error rather than risking an API call. This is exactly the kind of detail the schema lacks.

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 opens with a specific verb and resource: 'Check whether a domain name is registered, using real-time RDAP data.' It further clarifies the tool's purpose with concrete example questions like 'is domain-x.com available/registered' and 'when does domain-x.com expire,' making the scope unmistakable. There are no sibling tools to differentiate from, but the description is self-sufficient.

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?

The description explicitly provides a pattern of usage: 'Use for ... style questions' with three representative examples. It also states input requirements and behavior for malformed input. However, it doesn't explicitly mention when not to use the tool or provide alternative tools (none exist in context), so it falls just short of a 5.

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