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

With no annotations, the description carries the burden and does well: it discloses the cost ($0.005 per call over x402), the data sources (Coinbase's Bazaar, 'our index'), and the side effect of passing a payment ('the purchase completes inside this tool call'). It does not discuss rate limits or failure modes, but the main behavioral traits are covered.

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?

Two sentences with no filler: the core question is front-loaded, the returned data is compactly enumerated, and the cost/payment behavior is stated at the end. Every clause earns its place.

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 read-oriented verification tool with no output schema and no annotations, the description covers inputs, outputs, cost, and optional payment behavior. It does not define what 'real' means or how to interpret the returned metrics, but an agent has enough to invoke the tool and understand the result shape.

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 baseline is 3. The description adds real value beyond the schema by explaining the payment parameter as 'the same base64 payload you would put in the PAYMENT-SIGNATURE header' and clarifying that passing it completes the purchase within the call. The seller parameter is already well described in the schema.

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 opens with a clear question 'Is an x402 seller real?' and specifies the resource (seller host or payTo address) plus the data returned: Bazaar listings, 30-day payers/calls, repeat-buyer behavior, and Arc settlements. It is specific and actionable, though it does not explicitly contrast itself with sibling tools like x402_inspect or x402_payment_test.

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 clearly implies the use case: verifying whether an x402 seller is legitimate before engaging. It states the input forms ('a seller host or payTo address') and what data will be provided, giving clear context. However, it does not mention when not to use it or name alternative tools.

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