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

Description discloses the k-anonymity mechanism, that only a 5-character SHA-1 prefix is sent, and that the full password still travels in the URL. This adds valuable behavioral and privacy context beyond the annotations, which already declare read-only, idempotent, and non-destructive. No contradiction.

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?

Two tight sentences with the core behavior front-loaded and the sibling distinction second. No filler; each sentence earns its place.

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?

The agent gets everything needed to select and call the tool: purpose, privacy caveat, alternative tool guidance, and sufficient output meaning (existence and count). Annotations cover the safety profile, and the single parameter is fully documented.

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 fully documents the single parameter, including transmission mechanics and the warning to prefer password_check for real passwords. The description reinforces this with concrete terms like 'only a 5-character SHA-1 hash prefix' and 'k-anonymity', going beyond a bare type declaration.

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 action (checks breach appearance and count) against a named resource (HIBP). Explicitly distinguishes itself from password_check as breach-only. An agent can identify its function without opening the schema.

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?

Directly names password_check as the alternative and gives the deciding factor: password_check adds strength scoring and uses POST. Also warns that real passwords should not be sent in the URL, telling the agent when to prefer the sibling.

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