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

Annotations already establish the read-only, idempotent, non-destructive profile. The description adds valuable context beyond annotations: the exact return shape ('array of {date, rate} pairs sorted ascending by date'), business-day spot-rate granularity, the SDMX EXR data source, and the fact that no auth is required. This fully covers behavior an agent would need to know.

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?

The description is compact and front-loaded: purpose first, then date specification, return format, use cases, and data source. Every sentence earns its place and no redundant or promotional content exists.

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?

The description is complete for an agent to invoke the tool correctly. It states the resource (41 currencies vs NOK), how to specify date ranges, what the output looks like, and the data source/auth status. An output schema exists, and the description appropriately covers the behavioral aspects not encoded in schema.

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%, with each parameter already documented (ISO 4217 currency code, ISO 8601 format, defaults for start and end dates). The description reinforces the date-range concept but adds no new parameter-level information beyond what the schema provides, so the baseline of 3 applies.

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 opens with a specific verb and resource: 'Retrieve a historical time series of official Norges Bank exchange rates for any of the 41 available currencies versus NOK.' It clearly distinguishes the scope (history, NOK base) and differentiates it from the sibling norgesbank.fx.latest by emphasizing the historical series.

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?

Context for use is explicitly stated with concrete scenarios: charting NOK strength, backtesting currency strategies, and computing historical hedging costs. It does not explicitly name alternatives or exclusions, but the 'historical time series' framing and the listing of use cases make the intended usage clear.

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