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

The annotations already provide readOnly, idempotent, and non-destructive hints. The description goes beyond that by disclosing an important edge behavior: 'Refuses rather than guessing when a registry publishes no RDAP.' It also discloses that the output is aggregated into a single verdict and explains the underlying protocol (RDAP), which helps set expectations.

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 dense but every clause carries useful information: purpose, output, use case, refusal behavior, required input, and pricing/access. It is front-loaded with the core function and only later covers commercial details, making it easy for an agent to scan for selection and invocation.

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 one-parameter, read-only tool with an output schema and clear annotations, the description is remarkably complete. It covers the domain input, the source protocol, edge-case refusal, the combined verdict shape, and the access model. An agent has enough context to decide when to call it and what to expect.

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 100% for the single 'domain' parameter, so the schema already documents the input. The description only repeats 'Required input: domain' and does not add format examples, normalization details, or accepted variations. It meets the baseline but adds no parameter-level meaning beyond the schema.

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 direct question and then specifies the resource and outputs: 'Registration age, expiry and registry status for any domain' plus days to registration, days to expiry, registrar, EPP status codes, nameservers, and DNSSEC as one verdict. This is a specific verb+resource pairing and the GO/HOLD/STOP verdict clearly separates it from generic lookup tools.

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 grounds usage in a fraud-detection context: 'Domain age is the strongest cheap signal in invoice and vendor-impersonation fraud.' This tells an agent when this tool is the right call. It does not name alternative sibling tools or state when not to use it, but the use case is specific enough.

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