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

With no annotations, the description usefully discloses the $0.002 USDC charge per call, x402 payment mechanism, eip155:8453 network, deterministic behavior, provenance metadata, and possible calculation methods. It does not explicitly address read-only safety, failures, rate limits, or behavior when a current fixing is unavailable, so it is informative rather than exhaustive.

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 payment prerequisite is front-loaded, followed by a compact statement of the rate, source, returned metadata, and quality guarantees. Nearly every phrase contributes invocation-cost, provenance, methodology, or interpretation information, with only minor redundancy between "sourced" and "source attribution."

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 zero-input lookup without an output schema, naming the rate date, calculation method, and source attribution covers most of what an agent needs to interpret the response. It could still specify quote units explicitly as CNY per NZD, clarify fixing freshness or publication timing, and direct historical or conversion requests to appropriate siblings.

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?

There are no input parameters, so the zero-parameter baseline of 4 applies and there is no undocumented argument burden. The fixed currency pair and latest-rate scope adequately communicate the choices that would otherwise require inputs.

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 identifies the exact resource and scope: an official, latest NZD/CNY reference rate based on an ECB fixing or a peg-derived fallback. It also distinguishes the result from an estimate, but does not explicitly differentiate this fixed-pair tool from siblings such as fx_latest, fx_convert, or fx_cny_nzd.

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 terms "latest" and "official ... reference rate" provide clear selection context for an agent needing a current authoritative fixing rather than an estimated rate. It lacks explicit when-not guidance or routing to fx_timeseries for historical data, fx_convert for amount conversion, or fx_latest for a more general latest-rate lookup.

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