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

Annotations already indicate read-only, idempotent, non-destructive behavior, and the description adds substantial behavioral detail: k-anonymity via 5-char SHA-1 prefix, password not stored, return values (pwned, occurrence count, GO/HOLD/STOP), and pricing/auth requirements. This goes well beyond what annotations alone provide.

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 core purpose and flows naturally into privacy, output, pricing, and authentication details. Although longer than average, every sentence earns its place by providing actionable information an agent needs before invoking the tool. No redundant filler is present.

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 simple one-parameter tool with an output schema, the description is fully complete: it covers purpose, privacy behavior, return values, cost model, required headers, free-tier availability, and what is not offered. An agent has all necessary context to select and invoke this tool correctly.

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?

The input schema already fully documents the single required 'password' parameter with 100% coverage, so the baseline is 3. The description restates that password is required and mentions processing behavior, but it does not add format, length, or constraint details beyond the schema. It adds no substantive new parameter semantics.

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 precise question—'Has this password appeared in a dump?'—and names the specific resource: Have I Been Pwned Pwned Passwords via k-anonymity. It clearly distinguishes itself from email breach lookup tools by stating 'Email breach lookup not offered.' This is specific, action-oriented, and differentiated from sibling 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?

The description clearly communicates when to use the tool: when a user wants to check whether a password has appeared in a known password dump. It also gives an explicit exclusion ('Email breach lookup not offered') and states the required input. It does not name alternative sibling tools explicitly, but the usage context is unambiguous.

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