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

Annotations already declare readOnly and non-destructive behavior, but the description adds important context: it never signs, changes nothing, and each call is charged (not idempotent), clarifying that 'without paying' refers to the seller, not the tool itself.

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 purpose is front-loaded and the detailed fields, example, and pricing information are relevant. The description is dense but each sentence contributes to understanding the tool's function and cost model.

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 no output schema, the description lists the decoded fields and the listing-quality criteria, which is sufficient for an agent to understand what to expect. It could be slightly more explicit about output format but is largely 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 coverage is 100% so the single url parameter is fully documented. The description adds an example URL but no extra syntax or constraints beyond what the schema 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 (decode) and resources (402 payment requirements and listing-quality score), making the tool's function clear. However, it does not differentiate itself from the sibling tool check_x402_seller, which likely serves a similar purpose.

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?

It gives explicit usage context: 'Use before buying from an unfamiliar seller or to audit your own x402 listing.' There are no when-not conditions or alternative tool recommendations.

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