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

Annotations already declare readOnlyHint and openWorldHint, so safety is covered; the description goes beyond them by disclosing the pricing model ($0.002 USDC per successful call, x402 on Base/Solana/Arc) and that failed calls are not charged — a genuinely material fact for an agent deciding to invoke a paid tool. It does not cover rate limits or empty-result behavior, keeping it from a 5.

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 listed and what is not, followed by cost. The parenthetical field list is slightly redundant with the output schema but remains useful for quick scanning; no filler.

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 tool with an output schema and annotations in place, the description supplies the missing pieces: scope, the email-check exclusion, and the payment requirement. The enumerated return fields duplicate the output schema, which is mild over-explanation but nothing an agent needs is absent.

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 100% with a single required `domain` parameter that the schema already documents with an example ('adobe.com'). The description adds no format or normalization guidance beyond that, so the baseline 3 for full schema coverage 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?

Specific verb+resource ('Lists the data breaches HaveIBeenPwned has recorded for a domain') with the returned fields enumerated, and it explicitly distinguishes itself from the individual-email lookup that agents might otherwise assume. Given the sibling set is almost entirely unrelated search_* tools, no further differentiation is needed.

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?

States the context (public breach catalogue for a domain) and excludes the most likely misuse case ('not a check of individual email addresses — that needs a paid key and is not offered here'). It does not name alternative security_* siblings, but none are near-duplicates of this lookup, so the exclusion is the one that matters.

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