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

Goes well beyond the readOnly/idempotent annotations: discloses the price ($0.005 per call), that the default return is a paid request spec rather than data, that invalid input is refused before any charge, and the exact auth header format for the P0 key path. This is unusually rich; only the P0 balance/failure behavior under error conditions is left implicit.

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-loaded with the use case and data contents, with the purchase mechanics and pricing following. Dense and mostly earning its place, though the full buy-URL plus key-path explanation makes it long for a single-parameter 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?

Covers everything an agent needs for a single-param, no-output-schema tool: what data comes back, that the default response is a request spec with its own schema and example, cost, and both invocation modes. Nothing material is missing.

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% and the single parameter is fully documented there (URL accepted, host-only, IPs and private names refused). The description adds no syntax or format detail beyond the schema, 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?

States a specific verb and resource ('one report on a domain') and enumerates exactly what it contains: DNS records with SPF/DMARC parsing plus RDAP registration fields. Names the siblings it is not (domain_report_batch for several domains, check_email_address for a mailbox), so the agent can route without inspecting 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?

Opens with an explicit 'Use when' trigger, then gives explicit alternatives with their selecting conditions: domain_report_batch for multiple domains, check_email_address for a mailbox. It also states the decision between buying the raw x402 request versus using a P0 key.

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