European Central Bank reference exchange rates via Frankfurter. Latest or historical.
This tool declares no required parameters. Add optional parameters from the input schema as needed.
{
"id": 1,
"jsonrpc": "2.0",
"method": "tools/call",
"params": {
"arguments": {},
"name": "fx_ecb"
}
}| Name | Required | Description | Default |
|---|---|---|---|
| base | No | Base currency, default USD | |
| date | No | Historical date YYYY-MM-DD | |
| symbols | No | Comma-separated target currencies |
Changes observed during successful MCP inspections.
Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
With no annotations, the description carries the full burden. It discloses the data source and temporal behavior, but omits return format, rate limits, coverage, and error behavior. No contradiction exists, but transparency is only adequate for a simple read-only data tool.
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?
Two short, front-loaded sentences with no wasted words. The core capability and temporal scope are immediately clear.
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 three-parameter read-only lookup with a fully described input schema and no output schema, the description is nearly sufficient. It identifies the source and latest/historical behavior; only return-shape details are missing.
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 parameters are already documented in the schema. The description only indirectly maps 'historical' to the date parameter and adds no syntax or default details beyond the schema.
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 resource (ECB reference exchange rates) and source (Frankfurter), with latest/historical scope. It is clear what the tool returns, though it does not explicitly distinguish itself from sibling currency_rates.
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 phrase 'Latest or historical' implies that omitting the date returns current rates and providing a date returns historical rates. However, it does not state when to use this tool instead of a generic currency_rates sibling or mention any limitations.
Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.
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