Convert an amount between currencies

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

With no annotations, the description carries the full burden and adds real value: it discloses the plan requirement ('Starter plan and above') and the returned fields (rate used, given amount, converted amount). It does not cover failure behavior (invalid currency code, out-of-range date), which is the remaining gap for a no-annotation tool.

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?

Three short sentences, front-loaded with the action, then the return contract, then the access requirement. Nothing is redundant and no sentence could be dropped without losing information.

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 four-parameter tool with no output schema, the description covers the operation, the date variant, the return contents, and plan gating — enough to call it correctly. Only error/edge-case behavior is left unstated.

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%, so all four parameters — including the YYYY-MM-DD pattern for 'date' and the exclusiveMinimum on 'amount' — are already documented in the schema. The description's mention of the date conditional restates rather than extends the schema, so the baseline 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 gives a specific verb and resource ('converts an amount from one currency to another') plus the basis for the conversion (latest rate or a past date's rate). It implicitly separates itself from the rate-listing siblings (get_latest_rates, get_historical_rates) by returning a converted amount, but never names or contrasts them explicitly.

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 clearly states the condition that selects the historical behavior: supply 'date' for a past day's rate, omit it for the latest rate. There are no explicit exclusions or named alternative tools for the rate-only lookups, so it stops short of full routing guidance.

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