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

Annotations already declare readOnlyHint=true, idempotentHint=true, destructiveHint=false and openWorldHint=false, so the safety profile is fully covered. The description adds the return content (validity, balance, expiry), which is somewhat useful given there is no output schema, but it says nothing about behavior for an unknown/invalid code or any rate limits, so the added value is modest.

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?

A single front-loaded sentence with the verb first and the payoff ('whether it is valid, its balance and expiry date') at the end — no wasted prose. The inline format example is slightly redundant with the schema pattern, which keeps it from being a 5.

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 one-parameter read tool with no output schema, the description supplies the essential missing piece — what the call returns — while annotations cover safety. The only gap is behavior on an unrecognized code, which is minor for a tool this simple.

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?

With 0% schema description coverage, the description must carry parameter meaning, and it does name the format explicitly (FSF-XXXX-XXXX), matching the schema pattern in a human-readable way. It also clarifies that the single input may be a gift voucher or a studio credit code, which the schema does not distinguish; only a formal error-case explanation is missing.

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 gives a specific verb ('Checks') plus the resource ('gift voucher or studio credit code') and enumerates what the check yields (validity, balance, expiry date). This clearly separates it from the sibling buy_gift_voucher, which creates rather than inspects a voucher.

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 use case is only implied: an agent infers it should call this to verify a voucher before redeeming or accepting one. There is no explicit when-to-use statement, no mention of prerequisites (e.g., that the booking flow may need this first), and no named alternative or exclusion.

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