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

Annotations already declare readOnly/idempotent/non-destructive/openWorld, so the safety bar is low; the description adds genuinely new context: metered pricing ($0.005 USDC per successful call via x402 on Solana) and an equivalent HTTPS endpoint. It does not describe failure/refund behavior or rate limits, which matters for a paid call.

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-loads the core purpose and field list, then pricing and the alternate endpoint. Dense but each clause carries information; the pricing/endpoint sentence is slightly cluttered but not wasteful.

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?

No output schema exists, so the description responsibly enumerates return values, and it discloses cost and transport. Missing is error/empty-result behavior for invalid or unregistered domains, which would matter given the per-call charge.

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?

One required parameter with 0% schema description coverage, so the description must compensate. It implies the input is a domain but never specifies format (bare hostname vs URL vs IP) or whether an IDN/subdomain is accepted, leaving an ambiguity an agent can only resolve by trial.

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+resource ("RDAP registration age lookup") and enumerates the returned fields (registered/expiry dates, ageDays, daysToExpiry, registrar, status flags). It explicitly distinguishes itself from the sibling domain_intel as the cheaper subset, so an agent can route correctly 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?

Gives a clear selection condition: use this "when you only need age" and it is "faster/cheaper than full domain-intel." That covers the main alternative, though it does not mention domain_availability or state when-not to use the tool at all.

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