Pay for an x402 API

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

Annotations provide only openWorldHint, so the description carries the burden and delivers: payment is vetted by presign-guard, counts toward spending limits, over-limit triggers owner approval during which the call waits, and refusal returns an error with the reason. These side effects, gating, and error semantics go well beyond the single annotation.

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?

Front-loads the core action before detailing rails, precedence, and limits. Every sentence is substantive, though the parenthetical-heavy multi-chain exposition is dense and could be tightened.

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 but a clear statement that it 'return[s] the response,' plus full coverage of payment rails, spending limits, approval waits, error behavior, and price capping, the definition gives an agent everything needed to invoke it correctly in this open-world paid-API scenario.

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 all six parameters are already documented. The description adds only a marginal note that max_price_usd caps this call's price, largely echoing the schema, so the baseline 3 is appropriate.

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?

States a specific compound verb and resource: 'Call a URL that may answer 402 Payment Required and pay it in USDC from this wallet, then return the response.' This is clearly distinct from siblings like send_usdc (address-based transfer) and find_services, so an agent can select it without opening schemas.

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?

Gives clear context for when the tool applies (a URL that may demand 402 payment) and rich guidance on payment-rail selection with an explicit precedence order ('x402 comes first, then MPP evm, then Tempo'). It does not explicitly exclude or contrast alternatives such as send_usdc, so it stops short of full when/when-not guidance.

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