Historical rate on a date

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

Annotations already declare readOnlyHint and openWorldHint, and the description adds real value on top by disclosing the weekend/holiday fallback semantics, which an agent could not infer. It omits the response shape and any date-range limits (e.g. ECB data start date), but the key surprising behavior is covered.

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 tightly packed sentences: purpose first, then the edge-case rule, then a concrete invocation example. No filler; the example doubles as parameter documentation.

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 simple read-only lookup the description is close to complete, but with no output schema the agent gains no picture of the returned rate structure or error behavior for out-of-range dates. The undocumented 'symbols' parameter is also left unaddressed.

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 0%, so the description carries the burden: it documents the 'on' format (YYYY-MM-DD) and demonstrates 'base' with a default of EUR via the example. The 'symbols' parameter is never mentioned, leaving one of three parameters undocumented in both schema and description.

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?

States a specific verb, resource, and source ('Get ECB reference rates for a specific past date'), which separates it from latest_rates and timeseries by temporal scope. It does not name those siblings explicitly, so the differentiation is implied rather than stated.

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?

Gives clear context for when to call it (a specific historical date) and a non-obvious usage rule: weekends/holidays resolve to the most recent prior business day. No alternatives or prerequisite conditions are named, 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.