fx_rates

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

With no annotations, the description carries the full burden. It does add useful context: data source (ECB), free availability, and the return format (units per 1 EUR with as_of). However, it does not disclose update frequency, currency coverage, or whether the data is current or historical, leaving some behavioral ambiguity.

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, information-dense sentence that front-loads the key facts: official, ECB, free, and the rate direction. There is no fluff or repetition, and every word earns its place.

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 parameterless tool with no output schema, the description gives the essential details an agent needs to understand what it returns: 'units of currency per 1 EUR' and 'with as_of'. It could be more complete by mentioning historical vs current rates or viable currency codes, but the simplicity of the tool keeps this gap minor.

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?

There are zero parameters, and schema coverage is trivially 100%. The baseline for parameterless tools is 4, and the description appropriately does not attempt to explain nonexistent parameters. No additional parameter semantics are needed.

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 identifies the resource (ECB euro reference rates) and the data format (units per EUR with as_of), which distinguishes it from convert_amount_to_eur and other siblings. It lacks an explicit verb like 'get' or 'retrieve', but the tool name and context make the action 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?

There is no explicit guidance on when to use this tool versus alternatives such as convert_amount_to_eur. The intended use is implied for fetching exchange rates, but the description provides no exclusions or comparative context to help an agent choose between related tools.

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