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

Annotations already declare readOnlyHint=true and destructiveHint=false, so safety is covered. The description adds valuable behavioral context: the is_scheduled filter behavior and the size recommendation. It does not contradict annotations. It could add more (e.g., default ordering, return format), but it transparently describes the key usage nuances.

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 extremely concise and front-loaded with the core purpose ('List a candidate's email history'), followed by two actionable usage notes. Every sentence adds value with no fluff or repetition. It is an model of brevity without sacrificing essential information.

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?

Given the tool has 5 parameters, one enum, and no output schema, the description is relatively sparse. It does not mention pagination defaults (other than the size preference), ordering, or what the response contains. While the annotations cover safety, an agent might still be uncertain about expected return structure or pagination behavior. It is adequate for a simple list operation but not fully complete, hence a 3.

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 only 40%, with id and view described in the schema. The description adds meaning for is_scheduled (filter for pending scheduled messages) and size (prefer <=10), which is helpful. However, it does not explain the 'page' parameter or further clarify any of the other parameters beyond what the schema provides. The description partially compensates for the low coverage but not fully, warranting a 3.

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 states a clear verb ('List') and resource ('candidate's email history'), which unambiguously distinguishes this from sibling tools like hires_list_messages (which is not candidate-scoped) and hires_list_candidate_activities (which covers activities, not just email). The purpose is immediately obvious and specific.

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 provides clear usage context: it names the candidate-specific scope and gives a conditional for is_scheduled ('returns only pending scheduled messages'), which tells an agent what filtering to apply. It also offers a pagination preference ('Prefer size <= 10'). However, it doesn't explicitly mention when not to use it or name alternatives, but the implicit contrast with sibling tools (like hires_list_messages) is sufficient for a 4.

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