x402_compare

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

With no annotations, the description carries the full burden for behavioral transparency. It adds useful context such as 'from live data' (indicating dynamic pricing) and 'every rail the server offers' (indicating completeness). However, it does not disclose potential side effects, permissions, rate limits, or whether external network calls are made. For a non-destructive pricing query, this is a moderate gap, so a score of 3 is appropriate.

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 a single sentence that front-loads the core purpose (pricing) and includes a practical use case with a concrete action. Every word contributes value, making it highly concise and well structured.

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 tool's core purpose and use case, and the output schema handles return values. The main gap is parameter semantics, but given the tool's simplicity (3 params, one required) and the presence of an output schema, the description is reasonably complete. It loses one point for not compensating for missing annotations and schema descriptions.

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 0%, so the description must compensate. The phrase 'same API call' hints that url, method, and json_body define the call, but it does not explain each parameter or their expected formats. The parameter names are self-explanatory, but the description provides minimal additional meaning beyond the schema, which is insufficient for 0% coverage.

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 uses a specific verb ('Price') and clearly identifies the resource: the same API call across every rail the server offers. It lists example rails (Base/Solana USDC, Lightning, XNO), which distinguishes it from sibling tools like x402_quote and x402_pay by focusing on cross-rail comparison.

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 explicitly states when to use the tool: 'use this to verify which rail is cheapest instead of trusting documentation.' This provides clear use-case context. It does not explicitly name alternative tools, but the 'every rail' scope implicitly contrasts with single-rail quote tools, earning a score of 4 rather than 5.

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