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

The description goes beyond annotations by explicitly stating that no payment or transfer is initiated and that each call appends one record to the public ledger, making the non-read-only side effect transparent. It also explains the verification mechanism (SHA-256, ledger, verify_url). There is no contradiction with the annotations: readOnlyHint=false and idempotentHint=false align with the stated append behavior.

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 front-loaded with the most important safety information and is well organized, but it repeats the same non-payment and attestation concepts in Japanese and English. It contains more sentences than necessary for the additional value it provides, though the bilingual structure may be intentional.

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?

The description covers the domain (Japan construction/renovation, JPY), the integration point (Cart Mandate before user signature), side effects (public ledger append), and verification mechanism. It provides enough context for an agent to call the tool correctly, and an output schema is present, so return-value details need not be in the description.

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%, so the baseline is 3. The description adds context for quoted_price (fair-range verdict with within/above/below) and merchant (not used in judgment), but these are also present in the schema's field descriptions. It does not meaningfully augment what the schema already provides.

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 states a specific verb and resource: it issues a FairPriceAttestation for AP2 agents and explicitly distinguishes this from payment execution. It clarifies that no funds move, which sharply separates it from any payment-related sibling. The parallel authorization/value framing makes the tool's role in the AP2 flow unambiguous.

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 tells the agent when to use the tool: before asking the user to sign a Cart Mandate, and it explains when to pass quoted_price to get a fair-range verdict. It does not explicitly name alternatives or state when not to use it, but the usage context is clear enough for an agent to select it among siblings.

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