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

Beyond the read-only/idempotent/non-destructive annotations, the description discloses substantial behavioral context an agent cannot infer: closed-beta status with possible 401/403 refusal until enabled, a 1-credit cost that applies even to failed requests, and the required Exchange Rates API key. This is exactly the auth/cost/error disclosure the dimension rewards.

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?

Purpose is front-loaded in the first sentence, followed by the caveats that matter most. The prose is slightly choppy ('Exchange Rates API.' is a bare fragment) and could be tightened, but nothing is padding.

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 read-only lookup with fully documented parameters and an annotations set covering the safety profile, the description is nearly complete, adding beta, auth and cost context. It does not describe the response shape, which matters slightly more here since there is no output schema, but the omission is modest.

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 all three parameters (base, date, target) documented including patterns and examples, so the baseline is 3. The description adds no syntax, format, or edge-case meaning beyond what the schema already conveys.

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 and resource: fetching exchange rates for a base currency on a past date. The 'past date' scoping implicitly distinguishes it from the current-rates sibling get_exchange_rates, but it never names that sibling or any other alternative, so differentiation is left to inference.

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 via the 'past date' framing and the closed-beta caveat. The description never says when to prefer this over get_exchange_rates or convert_currency, nor does it name an alternative — but the beta and credit-cost notes do inform whether an agent should call it at all.

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