Exchange rate

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

Annotations already declare readOnlyHint and openWorldHint, so safety is covered. The description adds genuinely new context: no credential is required, there is no call cap, and the upstream provenance (ECB via Frankfurter) is named, which matters for trusting the numbers. It does not describe the response payload, but for a read-only lookup the disclosure is solid.

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-loads the source and constraints in the first sentence, then the rationale, then the date behavior. The yen-vs-dollar illustration is slightly decorative but does real work in justifying the tool. Roughly four sentences with little waste.

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?

There is no output schema, so the description should say what comes back — a single rate, a rate plus date, an object with both currencies — and it never does. Source, cost, and date semantics are all covered, but the return shape is left to inference for a tool whose whole value is the number it produces.

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%, so the baseline is 3, and the description clears that bar by explaining the purpose of the date parameter — a historical rate is what a cross-currency return calculation requires — which is intent the schema's 'rate as of this date' does not convey. It does not restate base/quote, which the schema already documents with examples.

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 names a specific resource and verb-equivalent operation (exchange rate between two currencies) and identifies the data source (ECB daily reference rates via Frankfurter). It is unmistakable against every sibling, none of which deals in FX, so an agent can select it without opening the 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?

It gives a clear trigger condition — 'needed whenever a screen leaves the US', with a concrete example of cross-currency balance comparison — and explains when to pass a date (historical rate for return calculations). It does not state exclusions or point to an alternative, but no sibling tool overlaps in purpose, so the routing guidance is effectively complete.

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