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

Annotations already declare readOnlyHint=true, idempotentHint=true, and destructiveHint=false, so the safety profile is covered. The description adds valuable behavioral context: it is a paid endpoint ($0.001 USDC), it performs a preflight check, and POST probes require explicit opt-in due to possible side effects. This goes beyond the annotations and helps the agent understand cost and side-effect nuances.

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 two sentences and front-loads the most critical information: the paid nature and the verify-before-pay purpose. The second sentence adds a necessary safety caveat. It is efficient, though the title already conveys some of the same information, slightly reducing the marginal value.

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 single-parameter tool with no output schema, the description covers the purpose, the cost, the safety profile, and the side-effect caveat. It does not describe the return format or what a successful verification looks like, but given the tool's simplicity and the annotations, the description is largely complete for an agent to decide whether to call it.

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 description implies the 'url' parameter is the endpoint to inspect, but it does not explicitly map the parameter to the behavior or explain URL format requirements beyond the schema's 'uri' format. With only one parameter, the gap is small, but the description could have explicitly stated that 'url' is the target endpoint.

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 names a specific verb ('verify-before-pay endpoint safety check') and a precise resource ('x402 payment preflight + PayTo verification'), and it enumerates the exact dimensions checked (payTo verification, quote price, network, asset, resource binding, x402 challenge compliance). This clearly distinguishes it from generic HTTP or resolution tools in the sibling list.

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 states when to use it: before an agent authorizes spend, and it explicitly warns that POST probes require caller opt-in because of potential side effects. It does not name specific sibling alternatives or exclusions, but the context is clear enough for an agent to select it over generic tools like resolve or url_parse.

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