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

With all annotations false, the description carries the disclosure burden. It does describe the return behavior (fx_rates object plus rate date), which is useful, but it does not mention whether rates are freshly fetched, whether external calls/failures are possible, or that the operation has no side effects. Acceptable but not rich.

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 tight sentences with no filler. The trigger condition is front-loaded, and every phrase adds value: when to call, what not to do, and what to expect back.

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 two-parameter tool with fully documented schema, the description adds the missing context: the multi-currency invoicing scenario and the shape of the return value. With no output schema, a bit more detail on the exact fx_rates object structure could help, but the cross-reference to expense_to_invoice and the rate date is sufficient for correct invocation.

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%, including the direction semantics of currencies and the meaning of target. The description adds no parameter-level meaning beyond the schema, 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 clearly states when the tool applies (rebill/invoice spanning multiple currencies) and what it produces (the fx_rates object expense_to_invoice takes, plus the rate date). It does not name sibling alternatives, so it stops short of fully explicit differentiation, but the purpose is specific and unambiguous.

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?

It gives an explicit trigger condition — 'when a rebill or an invoice spans more than one currency' — and an explicit alternative to avoid: asking the user for rates. It does not name sibling tools like convert or rates_latest, so exclusion guidance is contextual rather than exhaustive.

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