Sign Hosted x402 Challenge

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

Annotations (readOnlyHint=false, destructiveHint=false) are present. Description adds that it requires confirm: true and maxPriceUsd, returns a one-time header, and that the payment header is not surfaced when using the sibling. It does not elaborate on side effects beyond signing, but the annotations already cover the non-destructive nature.

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?

Two concise sentences, front-loaded with purpose, then usage guidance. No wasted words. Alternative tool named explicitly.

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 low-level helper with 6 parameters, annotations, and an output schema, the description covers purpose, usage constraints, and alternative. Could mention that it's local (already 'local helper') but otherwise complete.

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% with each parameter having a description. The description adds no further meaning beyond the schema; it only states the overall tool purpose and constraints. 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?

The description clearly states the verb ('signs a parsed x402 PaymentRequired challenge') and the resource ('returns a one-time Payment-Signature header'). It also distinguishes from the sibling tool sap_payments_call_paid_tool by noting that normal agents should prefer it.

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?

Explicitly says 'Use only when building a custom client; normal agents should prefer sap_payments_call_paid_tool' which provides clear when-to-use and when-not-to-use guidance. Also mentions requirements: 'Requires confirm: true and maxPriceUsd.'

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