apply_promo_code

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

No annotations exist, so the description must disclose behavior. It does not mention side effects (e.g., modifies cart total), idempotency, error conditions, or whether it is read-only. The mutation nature is implied but not explicit.

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 very short and front-loaded with the main action. It includes a structured 'Args' section, with no wasted words. However, it could be more comprehensive without losing conciseness.

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 an output schema, it is acceptable to skip return value details. However, the description lacks context about validation, constraints, or error handling, which would be useful for a mutation 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?

With 0% schema coverage, the description compensates by providing brief but clear definitions for both parameters: 'cart_id: The cart ID' and 'promo_code: The promotion code to apply'. This adds meaning beyond the schema's empty descriptions.

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 'apply a promotion code to the cart', with a specific verb and resource. It distinguishes from sibling 'apply_gift_card' by specifying 'promo code' versus gift card, but lacks explicit contrast.

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?

No guidance is provided on when to use this tool versus alternatives like 'apply_gift_card'. There are no prerequisites, restrictions, or context for usage.

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