Get FX rate

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

Annotations already declare readOnlyHint and destructiveHint, but the description adds valuable behavioral context: the ECB publishes once per business day (daily fix), non-ECB pairs fall back to Yahoo, and rates are indicative mid-market not dealable quotes. This goes beyond the annotations to explain data freshness and reliability.

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?

The description is a single dense paragraph but every sentence earns its place. The core function is front-loaded in the first sentence, followed by data-source caveats, a crypto exclusion, and a realistic usage warning. There is no fluff or repetition of schema data.

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 tool without an output schema, the description explains the key return values: the rate, change since prior session, and converted total when amount is given. It also covers data provenance, fallback behavior, and the indicative-vs-dealable caveat, making it comprehensive for an FX converter.

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 baseline is 3. The description adds meaning by explaining that 'amount' is 'Amount of the base currency' and that when given, the converted total is returned. It reinforces the schema's parameter descriptions and clarifies the conversion direction.

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 opens with 'Convert between two currencies at the latest published reference rate', which is a specific verb and resource. It clearly distinguishes itself from siblings by stating 'Use get_crypto_price for crypto — BTC and ETH are not currencies here', and clarifies the scope to fiat/ECB/Yahoo currencies.

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?

The description gives explicit when-not guidance: 'Use get_crypto_price for crypto' and excludes BTC/ETH. It also sets expectations about the rate being a daily fix rather than a live tick, helping the agent decide if real-time data is needed. This is more than just a list of alternatives—it provides contextual exclusions.

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