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

Goes well beyond the annotations by disclosing that no authentication is required, no credits are consumed, no wallet or token data is exposed, and that the response carries valid/invalid status with a reason. Those are exactly the operational facts an agent needs and that readOnlyHint/idempotentHint cannot convey.

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?

Four short sentences, front-loaded with the action and resource, then use context, then return shape and cost/safety guarantees. Every sentence carries distinct information with no 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?

With one fully documented parameter and no output schema, the description supplies the missing pieces itself: it describes the return value (valid/invalid plus reason) and the auth/credit profile. Nothing needed to invoke or interpret the call is absent.

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 coverage is 100% and the single parameter already documents the INSR-XXXXX format with a matching regex pattern. The description restates the format but adds no syntax, casing, or normalization detail beyond the schema, so the 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?

States a specific verb and resource ("Validate an INSR-XXXXX discount code") and scopes it to merchant backends during ACP/UCP checkout. It does not, however, distinguish itself from the sibling tool insumer_check_discount, which an agent could easily confuse it with.

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?

Gives a clear situational context: use it from merchant backends during ACP/UCP checkout to confirm validity, discount percent, and expiry. It stops short of naming alternatives or stating when not to use it (e.g. vs insumer_check_discount).

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