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

With no annotations at all, the description carries the full burden and does a lot: it discloses the cost ($0.002 USDC/call), the payment protocol and chain (x402, eip155:8453), the data provenance (ECB fixing, or peg when applicable), and the derivation method. It does not cover failure modes (unsupported/pegged pairs, stale-fixing handling) or caching behavior, which keeps it short of a 5.

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?

A single dense sentence with the payment terms front-loaded in a bracket, followed by what is returned. Every clause carries information, though the parenthetical method enumeration makes it slightly packed for one sentence.

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?

There is no output schema, so the description must convey the return shape, and it does: rate, rate date, method, source attribution. Combined with the disclosed price and protocol, an agent has nearly everything needed; only error/edge-case behavior is absent.

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 parameterless call by fully specifying the currency pair in the tool identity.

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?

States a specific resource (the PLN/SEK reference rate) with a named authoritative source (latest ECB fixing) and the exact nature of the value (fixing or official peg). The pair is unambiguous in both name and description, so an agent can distinguish it from the hundreds of other fx_* pair tools at a glance.

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 only implied by the pair-specific name; the description never says when to prefer this over fx_convert, fx_latest, or fx_timeseries, nor does it state that this is the single-pair endpoint for a fixed currency combination. No exclusions or prerequisites are given.

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