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 model ($0.002 USDC per call, x402, eip155:8453), the authoritative source (ECB), the derivation method (direct, cross via EUR, or peg-derived), and asserts determinism with no estimation. It stops short of failure/availability behavior (e.g., what happens on non-fixing days or if OMR's peg changes), which is the only notable gap.

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, front-loaded with the payment meter and then the core purpose, followed by the return components. Every clause (source, method, date, attribution, determinism) maps to something the agent actually needs; the bracketed pricing token is slightly noisy but justified for a paid endpoint.

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 tool this is close to complete: because there is no output schema, the description usefully enumerates what comes back (rate, rate date, method, source attribution) and warns that the value is deterministic rather than estimated. Only operational edge cases (weekend/holiday fixings, peg revaluation) are unaddressed.

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 is 4. The description correctly implies a parameterless call by naming the fixed currency pair and adds that the response carries a rate date and method, which helps the agent interpret the result even though no parameter meaning is needed.

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 precise verb+resource: the official NOK/OMR reference rate, and further narrows it to the latest ECB fixing or the official peg. The currency pair in the name plus this sentence leaves no ambiguity about what value is returned, and it is trivially distinguishable from the hundreds of sibling pair tools and from fx_convert.

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: the agent can infer this is the tool to call for a NOK/OMR spot reference rate. It never names alternatives such as fx_convert (for arbitrary conversion), fx_latest (for multi-pair snapshots) or fx_timeseries (for history), and gives no when-not conditions, so routing between the fx family is left to inference from naming.

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