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

Adds substantial behavior beyond the annotations: money moves (buyer pays before the supplier), VIA relays delivery and retains margin, there is no automatic signing or financial retry, and the retry must be identical. This matters because destructiveHint=false and idempotentHint=false alone would not tell an agent that a real charge occurs or that retries are unsafe.

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-loaded with the action and then the payment protocol; every clause carries operational weight (offer phase, retry identity, funding exclusions). Dense phrasing ('retains its margin', 'eligible external supplier') is compressed but not padding.

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 paid, open-world, non-idempotent tool with no output schema, the description covers the offer-phase return value and the payment protocol. It does not say what a successful execution returns or how delivery/status is retrieved (e.g., via_one_call_status), leaving a small gap.

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 67% and already documents maxUsdc and orderId, but the description adds the retry contract (identical task, maxUsdc, orderId) and the location of the buyer-signed payload in params._meta['x402/payment'] — a field that is not in the schema at all despite additionalProperties=false. That extra detail is valuable but slightly at odds with 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?

States a specific verb and resource: execute a VIA toll operation via the One-Call payment/delivery handler, and describes the two-phase x402 offer-then-pay flow. It is distinguishable from most siblings, though the first-call-returns-offer behavior overlaps with the sibling via_one_call_quote, which is never named.

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 a clear procedural context: first call without payment, then retry with an identical body after buyer approval. It also states exclusions ('Only supported tasks/suppliers', 'No automatic signing or financial retry', 'Prepaid comparison credits do not fund this tool'). It stops short of explicitly routing to via_one_call_quote or via_one_call_status by name.

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