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

With no annotations, the description must carry the behavioral disclosure burden. It does disclose that this is a merchant-only mutation and describes the redemption scenario. However, it does not mention idempotency, behavior if the voucher is already used, reversibility, or error conditions. For a state-changing operation, this is a moderate level of transparency but far from complete.

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 extremely concise and front-loaded: a short main clause followed by a clarifying parenthetical and a restriction. Both sentences earn their place without redundancy.

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 simple tool with two params and no output schema, the description covers purpose, usage context, and authorization restriction. It does not mention potential prerequisite checks (e.g., verifying status before marking) or failure semantics, but given the tool's simplicity and the lack of annotations, it is still reasonably complete.

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%: both voucher_id and voucher_code have clear descriptive text including the alternation between them and the format of the code. The description adds no additional parameter meaning, so baseline 3 is appropriate.

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 clearly states the action 'Mark a voucher as used' with the context 'redeemed by customer at merchant'. This specific verb+resource distinguishes it from sibling tools like check_voucher_status (read-only status check) and redeem_reward (rewards, not vouchers). The 'Merchant-only operation' qualifier adds further clarity on the intended actor.

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 indicates when to use the tool (at the point of customer redemption at a merchant) and adds a restriction ('Merchant-only operation'). However, it does not explicitly name alternatives or exclusions, such as using check_voucher_status for querying status before marking as used. The context implies the scenario but lacks explicit when-not guidance.

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