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

Annotations only flag readOnlyHint=false, openWorldHint=true, idempotentHint=false; the description goes well beyond by disclosing the exact price ($0.005), the currency and funding source (USDC from a configured wallet), budget-cap behavior, that failed/'not registered' lookups are still billed, and a prompt-injection warning that results are third-party data not instructions. This is exactly the context the annotations cannot carry.

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 purpose, then cost, then the payment/warning details, then the free alternative; every sentence carries operational information. Slight redundancy between 'Every lookup is a paid answer' and 'PAID: each call is charged in USDC', but nothing is wasted.

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 must cover return expectations, and it does state that even 'not registered' yields a billed answer, so the agent knows to expect a result rather than an error. It is close to complete for a paid lookup, though it does not characterize the fields returned.

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 both parameters are documented in the schema, including the nuanced confirm_over_cap semantics, so the baseline of 3 applies. The description's mention of budget caps adds context but no syntax or format detail beyond what the schema already supplies.

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 resource (registration data for a domain) and the mechanism (RDAP), which separates it from the other *_lookup siblings that query unrelated datasets. An agent can identify the capability without opening the 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?

Explicitly routes the agent to free_sample as a free preview before paying, which is actionable alternative guidance. It does not, however, state the conditions under which a paid domain-registration lookup is the right choice versus a free sample or another lookup tool, so it stops short of full when/when-not coverage.

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