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

With no annotations at all, the description carries the full burden; it does disclose two valuable traits: the call is destructive (the voucher is marked spent) and it is not repeatable (a second call yields ALREADY_SPENT). It omits auth/permission requirements, success return shape, and other error conditions, and "sandbox true" is ambiguous since no sandbox parameter appears in the schema.

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?

It is short and front-loads the mutation, which is good, but the telegraphic sentence fragments ("Merchant check.") cost clarity and the closing "sandbox true means no service is owed" is cryptic enough to require a re-read. Nothing is wasted, but compression has produced ambiguity rather than precision.

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?

For a destructive, unannotated, no-output-schema mutation, the definition is thin: it says nothing about success response, authorization, or where 'sandbox' originates, and one of two parameters is undocumented. Only the ALREADY_SPENT retry rule makes it partially usable.

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% and there are two parameters, so the description must compensate and largely does not: 'token' is never mentioned and 'merchant' is only hinted at by the word "Merchant check". An agent gets no explanation of token format, where it comes from, or whether merchant is optional.

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 phrase "Marks the voucher spent" gives a specific verb (marks spent) and resource (voucher), and it usefully corrects the misleading name 'verify' by revealing that this is the redemption step rather than a checksum check. The opening fragment "Merchant check" is vague on its own and no sibling (e.g. issue_voucher) is named, so an agent must infer that this is the opposite end of the lifecycle.

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?

There is no explicit statement of when to use this versus alternatives; the only conditional given is a retry outcome ("A second call is ALREADY_SPENT"), which is idempotency behavior, not usage guidance. The word "Merchant" implies a merchant-side redemption context, but that is inference rather than stated guidance.

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