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

With no annotations, the description carries the load and does well: it discloses the paid cost and payment protocol ($0.002 USDC, x402, eip155:8453), that the value is a deterministic official fixing rather than an estimate, and how the rate is derived (direct, EUR cross, or peg). It does not cover failure modes, e.g. what happens on a non-publication day or if the peg has changed.

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 plus a bracketed pricing tag, with the pair and source front-loaded. Every clause adds information, though the pricing preamble is slightly bureaucratic in placement and slightly disrupts the opening read.

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 source, derivation method, determinism, and the paid-call requirement, which is everything an agent needs to select and call it correctly. No return-schema explanation is owed given the tool's simplicity.

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 semantics are inherently simple; the description correctly signals that the currency pair is baked into the tool rather than passed as arguments, so an agent knows not to look for a params field. No further parameter elaboration is possible.

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 and scope: the official DKK/CZK reference rate, sourced from the ECB fixing (or official peg), and enumerates what the response carries (rate date, derivation method, attribution). An agent can distinguish this from the generic fx_convert or fx_latest siblings by the pair and the official-source framing.

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 the DKK/CZK pair, but there is no explicit guidance on when to prefer it over siblings such as fx_convert, fx_latest, or fx_timeseries, nor any note about caching or freshness expectations.

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