Coupon Update

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

Even with no annotations, the description discloses important behaviors: only provided fields change, the full list of editable fields, the expiry_date format, the valid value_type enums, and the return value. It does not mention permissions, reversibility, or null-field semantics, but it carries more behavioral weight than the typical update tool description.

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 compact and front-loaded: two sentences establish the core behavior and return value, then a tight list of editable fields adds the necessary detail. Every sentence earns its place; there is no fluff or repetition.

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 9 parameters, 0% schema coverage, and no annotations, the description covers the essential ground: update semantics, editable fields, validation formats, and the return. The existence of an output schema covers response shape. The remaining gaps are minor (e.g., whether providing null clears a field, error behavior if item_id not found) but do not seriously impede correct invocation.

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 0%, so the description must compensate. It lists every editable field and adds meaningful constraints: expiry_date format, value_type allowed values. It does not explain what each field represents (e.g., value vs. currency) or address how explicit nulls are handled, but it maps directly to the schema and provides more than the raw parameter names.

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 uses a specific verb ('Update') and resource ('existing item by id'), immediately distinguishing it from list, get, create, mark_used, and delete siblings. It also clarifies the partial-update semantics ('Only provided fields change'), so an agent knows exactly what this tool does and what it is not.

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 clearly conveys the context for use: updating an existing coupon by id without replacing the whole object. It does not explicitly name alternatives or exclusion conditions, but the sibling tool names make the distinction obvious and the partial-update behavior inherently separates it from create/delete. Slightly more explicit routing would earn a 5.

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