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

Annotations already declare readOnlyHint=true and openWorldHint=true, but the description adds substantial behavioral context beyond them: it discloses the residential proxy source, the per-call cost ($0.02 USDC), the payment mechanism (x402 on Base, Solana or Arc), and the fact that failed calls are not charged. It also clarifies that only the first page of results is returned.

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 front-loads the core action and is packed with useful details, but the long enumeration of return fields is somewhat redundant given the presence of an output schema, making it slightly over-stuffed. It remains efficient overall, with no filler sentences.

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?

Given the presence of a full output schema, complete parameter descriptions, and annotations, the description supplies all the extra context an agent needs: source, proxy, pricing model, and result scope. Nothing critical is missing for correct invocation.

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 schema already documents both parameters. The description mentions the locale concept and gives a few examples, but the schema provides a fuller list and the description adds no additional semantics (e.g., no guidance on default behavior or fallback). Baseline 3 is appropriate when the schema does the heavy lifting.

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: 'Back Market refurbished-product search on a country site', and the mention of Back Market distinguishes it from sibling ecommerce tools that target other marketplaces. An agent can immediately tell what this tool does and on which source.

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 gives clear context for when to use the tool (searching refurbished products on a specific Back Market country site) and lists the supported locales. However, it does not name alternatives or when-not-to-use conditions, so it falls short of the explicit routing guidance that would earn a 5.

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