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

Annotations already declare readOnlyHint=true and openWorldHint=true, so the safety profile is covered. The description adds no further behavioral context: nothing about what happens with an unknown/expired code, whether both codes can be supplied, or authentication needs. Adequate given the annotation coverage, but not enriching.

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 sentences, zero filler, with the core action front-loaded and the routing guidance second. Every clause carries information the agent needs.

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 an output schema present, return values need no explanation, and both parameters are documented in the schema. The only slightly under-specified point is the exactly-one-of constraint and error behavior for invalid codes, which lives in the schema rather than the description; overall complete for a simple single-item lookup.

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 100%, and the schema itself states that exactly one of code or serialized_code is required and explains the serialized-to-shared-code resolution. The description only restates the two parameter names, so baseline 3 applies.

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?

Specific verb ('Fetch one') plus resource ('KFC promotion') and the identifier it keys on ('redemption or serialized code'). It also names the sibling tools it is not, so an agent can separate this lookup from kfc_promotions (discovery) and kfc_nearby (store finder) without opening any schema.

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?

Routes the agent explicitly: use kfc_promotions to discover offers, kfc_nearby to find stores, implying this tool is for when a code is already in hand. The alternatives and the condition selecting each are stated rather than left to inference.

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