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

Annotations already declare readOnly, idempotent, non-destructive and openWorld, so the safety profile is covered. The description adds the meaningful context that this is a k-anonymity lookup against HIBP, implying only a partial hash leaves the client. It does not disclose the return shape (a set of hash suffixes with breach counts) or how the caller is expected to complete the comparison, which is the operationally important behavior.

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?

A single front-loaded sentence with no wasted words. It is efficient, though its brevity contributes to the gaps in workflow and return-value guidance rather than reflecting genuine completeness.

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?

There is no output schema and no explanation of what comes back. For a k-anonymity lookup this is a real omission: the caller needs to know it receives a list of suffixes and counts and must match the remainder of its hash locally. Without that, an agent could reasonably expect a boolean or a direct verdict.

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% and the schema already states 'First 5 characters of the SHA-1 password hash'. The description's 'SHA-1 hash prefix' restates the same fact without adding format, case-sensitivity, or validation details, 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: look up a SHA-1 hash prefix in the HIBP k-Anonymity database. The prefix-vs-full-password distinction does separate it from the sibling check_password, but only implicitly through the parameter wording, not through any explicit sibling differentiation in the description.

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?

There is no when-to-use guidance at all — nothing tells the agent to prefer this over check_password, or that this is the privacy-preserving variant of a password check. The agent must infer the workflow entirely from the tool name and the 5-character prefix constraint.

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