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

With no annotations, the description carries the burden. It specifies what data is returned (percentage, scope, validity, sales count) but does not explicitly state that the operation is read-only or safe, nor does it mention potential limitations like pagination, filtering by active/inactive, or ordering. The verb 'Lists' implies non-mutation, but the behavioral profile is only partially disclosed.

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, efficient sentence that front-loads the main verb and resource, then lists the key output attributes. No wasted words or redundant details, making it easy to scan.

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 simple nature (0 params, output schema present, no annotations), the description covers the essential information: what is listed and what fields are included. It falls short of full completeness only by not clarifying whether inactive discounts are included or if any implicit filtering/ordering applies, but this is a minor gap for such a straightforward listing tool.

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 tool has zero parameters and the schema coverage is 100% (an empty schema). The description doesn't need to explain parameters, so the baseline 4 applies. It adds no parameter-related confusion and correctly focuses on output content.

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 a specific action ('Lists') and resource ('your discount codes'), and enumerates the included data fields (percentage, scope, validity, paid sales usage). This distinguishes it from siblings like create_promo_code and set_promo_code_active, which mutate codes rather than list them.

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 explicit guidance on when to use this tool versus alternatives. It doesn't mention that it's appropriate for reviewing existing codes or that it should not be used for creating/updating them. The context signal of sibling names implies the distinction, but the description itself offers no routing or exclusions.

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