Get the Daily Reference Rate (16:00 London)

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

Annotations only declare readOnlyHint and openWorldHint, and the description adds substantial context beyond them: the rate is never revised, the cross is computed via USD and flagged `derived`, the latest table needs no key while a past date requires an API key on a paid plan, and it warns this is not the WM/Refinitiv fix nor a registered benchmark with a disclaimer to relay. This is exactly the auth/caveat/derivation detail the annotations do not carry.

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?

Front-loaded with the core definition, then usage, then parameter behavior, then caveats – a logical progression. It is dense with parentheticals and slightly long, but nearly every clause carries non-redundant information; little is pure 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?

With an output schema present, return values need not be explained, and the description still covers usage, sibling routing, parameter interaction, auth/plan requirements, and benchmark caveats. Nothing an agent needs to call this correctly is missing.

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% (baseline 3), but the description adds genuine semantics beyond the schema: omit source/target for the whole table vs. supply both for one pair crossed via USD and flagged `derived`, and omit date for the latest (no key) vs. supply it for a past day (API key, paid plan). This clarifies interaction and side effects the parameter docs alone do not convey.

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 ('once-a-day, never-revised mid-market rate') and defines the exact methodology (per-currency median of samples in a five-minute window at 16:00 London). It actively distinguishes this from the live-quote sibling (get_exchange_rate) and the official-rate sibling (get_official_rates), so an agent can route correctly without opening any schema.

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?

Explicit when-to-use is given with concrete scenarios ('index levels, return series, research datasets, month-end reports') plus explicit when-not-to-use via named alternatives ('rather than a live quote (get_exchange_rate) or an institution's official rate (get_official_rates)'). Nothing is left to inference.

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