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

Annotations disclose side effects (not read-only, idempotent, not destructive), and the description adds important behavioral context: it fails closed for JWS, AP2-shaped SD-JWT, and TAP-shaped evidence, and creates only a short RESERVED authorization with cumulative-budget allocation. It further clarifies it never executes payment, aligning with openWorldHint=false and idempotentHint=true.

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 three dense sentences, each carrying distinct information: usage constraints, validation behavior, and side-effect/processing boundary. There is no filler or repetition, and the front-loaded 'Use only for' immediately anchors the agent on the correct use case.

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 highly complex tool with deep nested schema and an output schema, the description adequately covers success behavior (qualifying ALLOW creates RESERVED authorization), failure behavior (fail closed for unsupported evidence), and the external processor flow. It is complete enough to position the tool within a broader payment pipeline without needing to explain return values.

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?

The schema description coverage for the tool description is 0%, and the description does not directly explain the 'envelope' or 'evidence' parameters. It provides high-level prerequisites like registered mandate and exact final purchase, but these are not mapped to the actual parameters, leaving the agent to rely solely on the schema for field-level meaning.

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 purpose: a production pre-payment authority gate that verifies cryptographic payment evidence. It distinguishes itself from sibling tools by explicitly scoping out full AP2 checkout/delegate-chain and Visa TAP structured-field/trust-store processing as external, making its role as the fail-closed evidence verifier unambiguous.

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 begins with 'Use only for a production pre-payment authority gate after...' and lists precise preconditions (registered mandate, pinned issuer key, fresh challenge, VERIFY-scoped key, exact final purchase, supported signed evidence). It explicitly states what remains external and clarifies that the tool never executes payment, directing the agent to a separate trusted gateway for the processor step.

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