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

Annotations already declare readOnlyHint=true and openWorldHint=true, so the safety profile is covered. The description adds one genuinely useful non-annotation trait — the $0.01 USDC cost and payment paths (x402 or credits) — but says nothing about rate limits, failure behavior, or domains without RDAP records.

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?

Two tight sentences: the capability and its returned fields come first, the pricing caveat second. Nothing is padding and the front-loading is correct.

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 single-parameter read-only lookup with no output schema, the description covers the returned fields and the cost model, which is enough to call it correctly. The unresolved overlap with lookup_domain_report and the title's unexplained 'Network Lookup' phrasing (a separate lookup_ip exists) are the remaining gaps.

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?

Only one parameter exists and schema description coverage is 100%, so the schema already documents 'domain'. The description adds no format detail (TLD requirements, IDN handling) beyond the schema, so baseline 3 applies.

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 resource — domain registration data (registrar, created/expires, status, nameservers) — and the retrieval mechanism, RDAP. However, it offers no differentiation from the closely related sibling lookup_domain_report, which an agent would need to distinguish between.

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?

There is no guidance on when to use this tool versus lookup_domain_report, lookup_dns, or lookup_ip. The only supplementary sentence covers billing, not selection or preconditions.

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