Derive Payment Address (BRC-42/29)

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

Annotations already declare readOnly, idempotent, and non-destructive hints. The description adds substantial behavioral context: determinism per invoice, on-chain unlinkability, independent computability by payer/payee, and the prerequisite of an initialized wallet. It also states the return structure (address, publicKey, invoiceNumber), which is not covered by annotations or an output schema.

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 well-structured and appropriately sized: a single-sentence summary, a short paragraph of behavioral context, a prerequisite note, and clearly labeled Args/Returns sections. Every sentence adds information; there is no fluff or repetition. The most important facts are front-loaded.

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 all necessary aspects: purpose, key behavioral traits, prerequisite, the input parameter, and the return shape. It also situates the tool within the x402 payment flow, making its use case clear. There is no obvious missing context.

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 input schema already documents the single parameter (invoice number) with a good description ('Invoice/reference string; deterministically derives a unique payment address'). The description's Args section merely restates 'invoice/reference string' without additional parameter-level detail. The prose adds context about behavior, but not about the parameter's format or constraints beyond the schema. Thus the description adds no significant value over the schema's parameter documentation.

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 opens with a specific verb ('Derive') and resource ('unique, deterministic payment address'), clearly differentiating it from sibling tools. It also names the standard (BRC-42/29) and explains the core use case (x402 payment flows), leaving no ambiguity about what the tool does.

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 provides clear context: it explains the deterministic relationship between invoice and address, the unlinkability property, and that a wallet must be initialized. It does not explicitly state 'use this instead of X' or enumerate exclusions, but the context is specific enough that an agent would know when to invoke it. The lack of explicit alternative comparison is the only gap, matching the 'clear context, no exclusions' level.

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