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

The description adds substantial behavioral detail beyond the annotations: it reads no chain, sends nothing, validates the authorization against the bill's payTo and exact amount, checks the bill has not run out, and recovers a 65-byte signature to the payer. These details are consistent with the read-only, idempotent, non-destructive annotations.

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 compact and front-loads the prerequisite, then explains the result and validation behavior, and finishes with the exact next action. Every sentence earns its place with no redundant restatement of schema or annotations.

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 tool with three required parameters and no output schema, the description provides everything needed: prerequisites, output format and header names, validation behavior, and the next request step. No critical information is missing.

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 parameters are already well documented. The description adds useful semantic context by explaining that the authorization is checked against the bill's payTo and exact amount, and that the signature is recovered to its payer, though it does not further elaborate on the string/object flexibility of the parameters.

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 clearly identifies the tool's output: the x402 payment header the merchant reads, with both header name variants (PAYMENT-SIGNATURE and X-PAYMENT) and base64 JSON format. It also distinguishes this from credit_bill by framing it as the subsequent step after credit_bill and the wallet's signature.

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 states the explicit precondition ('After credit_bill and the wallet's signature') and the exact follow-up action ('Send the same request again with header.name set to header.value'), leaving no ambiguity about when and how to use the tool.

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