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

Goes well beyond the readOnlyHint/openWorldHint annotations: discloses the pricing model ($0.02 USDC per call via x402), the no-charge failure condition, deterministic behavior ('No AI involved'), and TLD coverage breadth. These are material facts an agent needs before invoking a paid, open-world tool.

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?

A single dense paragraph that front-loads the returned data before moving to usage, coverage limits, and price. Every clause carries information, though the enumeration of TLDs and flags is slightly sprawling.

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, no-output-schema tool, the description covers return contents, trust-judgment purpose, supported/unsupported TLDs, pricing, and billing exemptions — everything an agent needs to decide and call correctly.

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?

Single parameter with 100% schema description coverage, so the schema already documents that it accepts a domain name or URL with an example. The description adds only TLD applicability context, not new meaning about the parameter itself; 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 verb+resource (domain age/registration lookup plus live DNS) and enumerates the exact data returned: created, expires, registrar, status, nameservers, SPF, DMARC. It is unmistakably distinct from siblings like check_doi, check_links, robots_check.

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 use case ('judge how trustworthy a site is') and documents applicability limits (works for most TLDs; no charge when the registry has no public lookup such as .de, .jp, .co). It does not explicitly name a sibling alternative, but the siblings cover entirely different resources, so no routing ambiguity remains.

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