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

Annotations already mark the tool as idempotent and non-destructive. The description adds valuable behavioral detail that only supplied fields are changed, implying unspecified fields are preserved. It does not mention side effects or validation, but it does not contradict annotations.

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?

Two short sentences, front-loaded with the tool's purpose, and every word earns its place. There is no redundancy or unrelated detail.

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?

With a 10-parameter schema fully documented, an output schema present, and annotations covering idempotency and safety, the description is complete enough for correct invocation. The essential PATCH semantics are explicitly stated, and nothing critical is missing.

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 schema provides 100% coverage of parameter descriptions, so the description only needs to add semantics beyond that. The phrase 'Pass only the fields you want to change' clarifies that all fields except promotionId are optional and that omitted fields retain their current values, which is valuable PATCH-style guidance.

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 the specific verb 'Update' with the resource 'promotion' and clarifies 'existing promotion', distinguishing it from create_promotion, delete_promotion, and get_promotion. The instruction 'Pass only the fields you want to change' clearly identifies partial-update semantics.

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?

States this is for modifying an existing promotion, which implies it is not for creating, deleting, or validating promotions. It lacks explicit exclusions or alternatives, but the phrase 'existing promotion' plus the partial-update instruction provides clear usage context.

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