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

With no annotations, the description carries the full burden and does well: it discloses the paid cost and protocol ($0.002 USDC/call, x402, eip155:8453), the authoritative source, the peg fallback, and that the value is deterministic rather than estimated. It omits freshness guarantees, caching, and failure behavior when no fixing exists.

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 tight clauses with the cost prefix front-loaded and the source/method details following. Every phrase earns its place: cost, source, fallback, output fields, and determinism are all load-bearing.

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-parameter, annotation-free tool with no output schema, the description supplies the essential context: source, method, date field, attribution, and the peg caveat. Only the concrete return shape and error conditions are left unspecified, which is a minor 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?

The tool takes zero parameters, so the baseline of 4 applies. The description correctly implies the currency pair is fixed by the tool identity itself, requiring no further input.

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 names a specific resource (the official CZK/XAF reference rate) and its provenance (ECB fixing or official peg), so the agent knows exactly what data comes back. It does not explicitly differentiate itself from the many sibling pair tools such as fx_convert or the inverse fx_xaf_czk, leaving that inference to the naming convention.

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?

There is no when-to-use or when-not-to-use guidance, and no pointer to alternatives like fx_latest, fx_timeseries, or fx_convert despite hundreds of sibling FX tools. The note about XAF being pegged explains data behavior but not selection criteria.

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