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

Annotations already cover readOnlyHint, idempotentHint, destructiveHint=false, and openWorldHint, but the description goes well beyond them: it discloses the k-anonymity mechanism (only a 5-char SHA-1 prefix leaves the server), that the password is not stored, the return signal (pwned + occurrence count and GO/HOLD/STOP), and the pricing/auth model. This is exactly the extra behavioral context an agent needs for a security-sensitive 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?

Front-loaded with the core question and resource, then layered with mechanism, exclusions, and pricing in tight fragments. It is information-dense rather than padded, though the payment details make it longer than strictly minimal.

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-param tool with an output schema, the description still adds privacy guarantees, the output signal shape, and the full payment/auth model. An agent can decide whether to call it and how to pay without consulting anything else; 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?

Only one parameter exists and schema description coverage is 100%, so the baseline is 4. The description reinforces that 'password' is the required input, but adds no format or syntax guidance beyond the schema, which is acceptable for a single unambiguous parameter.

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 opens with a specific question-form verb+resource ('Has this password appeared in a dump?') and names the exact data source and mechanism (Have I Been Pwned Pwned Passwords via k-anonymity). It explicitly distinguishes itself from the closest sibling concern by stating 'Email breach lookup not offered', so an agent can separate this from email_verify-style tools.

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 context is clear: check whether a password appears in a dump, with the exclusion of email breach lookup. It also spells out the payment conditions (x402 on Base, prepaid x-credit-token for unlimited calls, no free tier, no API key). It stops short of naming an explicit alternative tool for email breach checks, so it is not a full 5.

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