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

With no annotations present, the description carries the full burden and does well: it discloses the paid x402 gate and price ($0.002 USDC/call on eip155:8453), the upstream source (ECB), how the rate is derived (direct, cross via EUR, or peg-derived), and that results are deterministic with no estimation. It stops short of stating freshness/caching guarantees or stale-fixing behaviour on non-publication days.

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 dense sentences with no filler, and the core purpose is stated immediately after the payment tag. The bracketed pricing prefix front-loads cost and protocol details ahead of what the tool actually does, which slightly delays the agent's recognition of the resource.

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, no-output-schema lookup, the description covers the essential unknowns: what value is returned, its provenance, the derivation method, the date field, and the payment cost. An agent has everything needed to decide to call it and to interpret the response fields.

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 there is nothing for the description to disambiguate; the baseline of 4 applies. The description correctly implies a fixed pair with no date or amount input, which is the right expectation to set for a parameterless tool.

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 the exact resource (the CZK/PLN reference rate) and its provenance (latest ECB fixing, or official peg), so an agent knows precisely which currency pair and which fixing this returns. It does not, however, distinguish itself from adjacent siblings such as fx_pln_czk (inverse), fx_czk_eur, fx_convert, fx_latest or fx_timeseries, so the pair must be inferred from the tool name alone.

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?

Usage is implied rather than stated: an agent can infer this is the tool for a single CZK/PLN spot reference rate. There is no explicit when-to-use/when-not guidance, no mention that fx_convert should be used for conversion math or fx_timeseries for history, and no note about what to do if the pair is the wrong direction.

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