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

Annotations cover the safety profile (non-readonly, open-world, idempotent, non-destructive), and the description adds genuinely useful behavior: codes are single-use, no expiry, offered in en or ja, and 'treat codes like cash' warns of value-loss risk. The payment/x402 mechanics themselves live in the schema rather than the description, which is acceptable given annotation coverage.

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 that leads with the core offer and packs pricing, unit count, languages, expiry, and a cautionary note efficiently. Dense but readable; nothing wasted.

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 not be explained, and the description covers pricing, unit economics, language options, and expiry. The only minor gap is that the actual acquisition/payment flow is delegated entirely to the schema, but that is reasonable here.

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?

There is only one optional parameter and schema coverage is 100%, so the x_payment semantics (omit to receive payment requirements without being charged) are already fully documented. The description's '$19.90 payment' ties loosely to that parameter but adds no syntax or format 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 resource and verb-act: purchasing a volume bundle of credit codes for style_report at $19.90 for 10 units. It names the sibling product (style_report) and contrasts unit pricing ($1.99 vs $2.99 single), so an agent can distinguish this pack purchase from the single-report tool.

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 price comparison ($1.99/unit vs $2.99 single) implies 'use this when buying multiple reports', but there is no explicit when-to-use or when-not-to-use statement, nor a named alternative. Usage is left to inference from the pricing hint.

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