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

Annotations declare readOnlyHint=true, idempotentHint=true, destructiveHint=false, indicating safe read operations. The description adds the detail that the tool returns UNKNOWN when conditions are absent or manual review is required, which is a behavioral trait beyond annotations. However, it lacks disclosure of other aspects like rate limits or auth needs.

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 concise sentence that front-loads the core purpose and key behavior (UNKNOWN return). Every word adds value, with no redundancy or filler.

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 presence of a complete input schema, annotations, and an output schema (indicated), the description sufficiently covers the tool's behavior. It could mention error handling or prerequisites, but for a simple eligibility check, the UNKNOWN detail adds necessary context. Slightly incomplete for a fully comprehensive view.

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 covers all 5 parameters with 100% description coverage, providing detailed meanings for each (e.g., enums, constraints). The tool description does not add additional parameter-level context beyond what the schema already provides, so it meets the baseline with no extra value.

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 tool evaluates return eligibility for US consumer subscription purchases under versioned source-backed rules, and explicitly mentions the UNKNOWN return state. This is specific and distinguishes from sibling tools like refund_eligibility or cancellation_penalty.

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 no guidance on when to use this tool versus alternatives (cancellation_penalty, refund_eligibility, trial_terms). It does not mention prerequisites, context, or exclusions. The only implicit hint is 'US consumer subscription purchase', which is not sufficient to differentiate usage scenarios.

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