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

Annotations already declare readOnly/idempotent/openWorld, so the safety profile is covered. The description still adds material context beyond them: the IANA bootstrap resolution step, the exact return payload, and the paid-access model ($0.01 USDC via x402 on eip155:8453), which is essential to know before calling.

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?

Three sentences, front-loaded with what is returned and followed by purpose and price. The opening clause duplicates the tool title almost verbatim, which is slight waste, but nothing else is padding.

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 usefully enumerates the returned fields, which is the right call. What is missing is failure behavior (unknown TLD, domain not found, bootstrap failure) and whether results are cached — relevant for a paid, network-dependent tool.

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 0% for the single required 'domain' parameter, so the description must carry the meaning. It only implies the parameter via 'for the TLD' and adds nothing about accepted format (bare FQDN vs URL, IDN, subdomains, maxLength 300). Adequate but leaves a real gap.

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 names a specific verb and resource ('Looks up the registry RDAP server for the TLD') and enumerates exactly what fields come back: registrar, registration/expiry dates, age, EPP status, nameservers, DNSSEC. It is clearly distinct from dns_lookup-style siblings, though it never explicitly contrasts itself with them.

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?

It offers one usage cue ('Useful for fraud and phishing checks (young domains)'), which points an agent at a legitimate scenario. There are no exclusions, no alternatives named (e.g. dns_lookup, web_metadata), and no guidance on what to do when a TLD has no RDAP server.

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