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

Annotations already establish read-only, idempotent, open-world behavior, and the description adds genuinely non-obvious operational context: 0.005 USDC per successful call via x402 on Base, with errors free. It does not mention wallet/auth prerequisites or rate limits, but the paid-call disclosure is meaningful value beyond the annotations.

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 sentences, both front-loaded: the capability and its modes come first, the pricing/error policy second. Every clause carries information an agent needs; no filler.

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?

With no output schema, the description carries the burden of describing results, and it does so at a high level (latest day vs. daily series) while also covering cost and error behavior. It omits response shape details and handling of invalid or unpublished currency codes, leaving a small gap for a zero-required-parameter tool.

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?

Schema coverage is 100%, so the baseline is 3, and the description earns an extra point by framing the parameters as mode selectors and adding the weekend/holiday fallback rule and the 366-day cap. It stops short of restating syntax like the ISO 4217 comma-separated format, which the schema already covers.

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?

Names a specific verb and resource (official Norges Bank exchange rates against NOK) and immediately enumerates the three supported access modes: latest business day, a single day, or a series up to 366 days. Nothing in the sibling list overlaps, so an agent can identify this tool unambiguously.

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?

Explains the conditions for each mode (one day falls back to the prior business day on weekends/holidays; a series is capped at 366 days) and states the cost model up front. It does not name an alternative tool or explicitly say when not to use it, but there is no competing sibling, so guidance is effectively complete.

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