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

Annotations only declare readOnlyHint=false, openWorldHint=true and idempotentHint=false; the description goes well beyond them by disclosing the exact price ($0.005, product rdap.domain), the USDC wallet billing model, budget caps, and the fact that failed/negative lookups are still charged. It also flags results as untrusted third-party data, a prompt-injection warning the annotations do not 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?

Cost and paid status are front-loaded, and the free_sample pointer lands last where it functions as a call to action. There is mild redundancy between 'Every lookup is a paid answer' and 'PAID: each call is charged', but every sentence carries a distinct operational fact.

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 two-parameter paid lookup with no output schema, the definition covers cost, billing mechanics, budget enforcement, data trust, and the free alternative. What it omits is the shape of a successful RDAP answer and what happens when a budget cap blocks the call, which would round it out.

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 schema already explains both domain and confirm_over_cap in detail, including that the flag is ignored for clients that can ask the user. The description only supplies surrounding payment context (budget caps) that makes the flag meaningful, adding little parameter-level detail of its own. Baseline 3 is appropriate.

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 and mechanism: registration data for a domain via RDAP. An agent immediately knows this returns registry/registration records rather than company profiles or market data. It does not explicitly contrast with the nearest sibling lookups, which keeps it from a 5.

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 before paying, which is the key decision for this tool. It also states that negative answers ('not registered') are still billed, which shapes when a lookup is worth making. It gives no guidance on when this beats other domain-adjacent lookups, but the primary alternative is named with its condition.

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