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

Annotations already declare readOnlyHint=true, idempotentHint=true, and destructiveHint=false, covering the safety profile. The description adds minimal behavioral context: 'currently loaded into HIBP' indicates the result reflects the current state of HIBP's data. It does not mention rate limits, error conditions, or any other operational behavior, but given the annotations, this level is acceptable.

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 a single sentence of 13 words, front-loaded with the verb and resource. There is zero waste and the key differentiator (latest breach) is immediately clear. It is appropriately sized for the tool's simplicity.

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 very simple tool with one optional parameter and a full output schema, the description is complete. The safety profile is covered by annotations, the parameter is covered by schema, and the purpose is clear. An agent has everything needed to 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 schema description coverage is 100%, so the single parameter 'response_format' is fully documented in the schema with its enum and default. The tool description adds no extra meaning to this parameter beyond what the schema already states. Baseline of 3 is appropriate.

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 clearly states the verb 'Return' and a specific resource: 'the most recently added public breach currently loaded into HIBP'. It distinguishes this tool from siblings like hibp_list_breaches (which lists all) or hibp_get_breach (which fetches by name), as it focuses on the most recent addition.

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 implies usage: if you need the most recently added breach, use this tool. However, it does not explicitly contrast with alternatives or provide when-not-to-use conditions. There is no mention of 'use instead of list_breaches' or 'only when the latest breach is needed'. The guidance is implicit rather than explicit.

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