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

Annotations already provide readOnlyHint, idempotentHint, and destructiveHint, covering safety and side effects. The description adds that it returns one or more time series with period/value pairs, which is useful beyond the schema. However, it does not disclose potential pagination, rate limits, or other behavioral traits. With strong annotations, the description's additional value is moderate; a 3 is appropriate.

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 two well-structured sentences. It front-loads the core purpose, includes a helpful parenthetical with concrete examples, and ends with expected return format. No fluff or redundancy; every clause adds value.

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?

Given the tool's moderate complexity (4 params, output schema present), the description covers the source series, scope, return format, and rate definition. It references the monthly nature and series ID. The output schema handles return structure, and the description gives sufficient context for an agent to call it correctly without missing critical information.

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 description coverage is 100%, with each parameter (country, start_period, end_period, max_series) documented in detail, including examples and defaults. The tool description does not add significant parameter-level semantics beyond the schema, though it does contextualize the country code within the BIS reference-area list. Per the rubric, since coverage is high, baseline is 3.

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 states a specific verb ('Fetch'), a clear resource (central bank policy interest rates from the BIS monthly series WS_CBPOL), and gives concrete examples (Federal Funds rate, ECB refi rate). It distinguishes itself from sibling tools like exchange_rates and property_prices, and clarifies the scope ('Covers dozens of central banks worldwide').

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?

The description implies when to use it: for central bank policy rates across many countries, citing the BIS as a broad source. It gives context on what the rate represents and the series ID, but does not explicitly name alternatives (e.g., specific central bank endpoints) or state when to prefer those. The broad-coverage phrase is helpful but not an explicit routing instruction.

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