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

Annotations cover the safety profile (readOnly, openWorld, non-destructive), and the description adds substantial context they don't carry: a per-call charge of $0.009 USDC via x402, which networks are supported, that x402 MCP clients pay automatically, a DNS fallback for TLDs lacking RDAP, and a free sample call. The payment requirement materially changes how the tool is invoked, which is exactly the disclosure that matters here.

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?

The description is front-loaded with the scope of the check and then the payment logistics, and every clause carries information. The opening sentence is dense and long, but nothing is padding; the price and sample details earn their space for a paid tool.

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 does the work of explaining the returns (0-100 score, grade, findings), the inputs, the payment flow, and the RDAP fallback, which is close to complete. It stops short of detailing rate limits or what 'findings' contain, leaving minor gaps for a tool this rich.

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% for the single 'domain' parameter, which is already documented in the schema with an example. The description adds nothing beyond restating that domain is required, so the 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 verb (check) applied to a specific resource (a domain) and enumerates the exact scope: RDAP registration data, DNS records, and email security (SPF, DMARC, DKIM). The phrase 'in one call' signals it aggregates what siblings like dns_lookup, whois, and email_verify do separately, so an agent can distinguish it without opening schemas.

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?

Usage is implied rather than stated: 'in one call' suggests this is the bundled alternative to the narrow dns_lookup/whois/email_verify siblings, but no explicit when-to-use or when-not-to-use guidance is given and no sibling is named. An agent must infer the routing itself.

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