Frankfurter — Latest ECB Exchange Rates

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

Annotations already declare readOnly/idempotent/openWorld/no-destructive, so safety is covered. The description adds genuinely useful behavioral context beyond them: update cadence (~16:00 CET each business day), no auth required, public-domain ECB data, and the 33-currency coverage. It stops short of describing response shape or pagination, which the output schema presumably handles.

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?

Purpose, source, cadence, and parameters are front-loaded and each sentence carries information. The trailing 'Ideal for FX dashboards, invoicing, and multi-currency apps' is mild filler that doesn't guide behavior, keeping it just under a 5.

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?

With annotations covering safety and an output schema covering returns, the description supplies the remaining context an agent needs: data provenance, freshness cadence, auth-free access, and base/amount/symbols capabilities. Only the absence of sibling routing guidance leaves a small gap.

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 three parameters (base, amount, symbols) are already fully documented in the input schema, including the supported currency enum list. The description restates default EUR and amount scaling for 'instant conversion' but adds no syntax or format detail beyond the schema. Baseline 3 is appropriate.

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 and resource ('Get the latest ECB reference exchange rates'), names the data provider and endpoint, and scopes the result (33 currencies relative to a default base). An agent can immediately distinguish it from the historical/series/list siblings by the 'latest' framing.

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 closing sentence 'Ideal for FX dashboards, invoicing, and multi-currency apps' implies use context, but it never names an alternative tool or states when NOT to use this one. The sibling frankfurter.currency.historical and similar FX tools (finance.currency.ecb, norgesbank.fx.latest) are not referenced, so routing among them is left to inference.

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