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FXRate: Exchange rates for one base currency

fx_rates

Read-onlyIdempotent

All ECB reference exchange rates for a base currency (default EUR), or only the listed quotes, latest or on a past date. Free: 30 calls/day per IP, then $0.001 per call.

[FXRate via YourAITools MCP Hub] Free tier: same as FXRate's own MCP server (call without payment and without tier). Paid: rates $0.001 per call, with a credits key (Authorization: Bearer yatc_...) or x402 (USDC; the hub returns the payment terms). Failed tool calls aren't charged: credits are refunded automatically and x402 payments only settle on success.

Tool call template

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_rates"
  }
}

Input Schema

Name	Required	Description
`base`	No	Base currency (default EUR): ISO 4217 code, e.g. USD, EUR, GBP, JPY (31 supported)
`date`	No	Optional YYYY-MM-DD (default: latest). Weekends/holidays use the previous ECB rate.
`tier`	No	Paid tier: rates $0.001. Omit tier (with no credits key or x402 payment) to use the free tier.
`quotes`	No	Optional comma-separated currency codes (default: all 30)

Schema Changelog

Changes observed during successful MCP inspections.

Changed2 schema fields changedOct 30, 2026
- addedInput schema / properties / base / examples
```
Added value: +[
+  "USD"
+]
```
- addedInput schema / properties / quotes / examples
```
Added value: +[
+  "EUR,GBP,JPY"
+]
```
AddedOct 25, 2026

TDQS

A3.6/5.0

Behavior4/5

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

Annotations already declare readOnly, idempotent, open-world and non-destructive, yet the description adds substantial context: a 30 calls/day per-IP free cap, $0.001 per-call paid rate, auth via Bearer yatc_ key or x402 USDC, and the guarantee that failed calls are not charged. What is missing is any indication of the response shape, which matters since there is no output schema.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Conciseness3/5

Is the description appropriately sized, front-loaded, and free of redundancy?

The first sentence is crisp and front-loaded with the core behavior. The second paragraph, however, is hub/billing boilerplate that repeats the free/paid distinction already encoded in the tier enum and is longer than the functional description itself.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Completeness4/5

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

For a four-parameter read-only lookup with annotations and no output schema, the definition covers cost, rate limits, auth, and date fallback behavior adequately. The remaining gap is that an agent cannot predict what the response contains (rate map, source, date echo), which the description would need to supply.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Parameters3/5

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema description coverage is 100%, so all four parameters (base, date, tier, quotes) are already documented with defaults and examples. The description only echoes the base-currency default and the quotes filter, adding no syntax, format, or edge-case detail beyond the schema. Baseline 3 applies.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Purpose4/5

Does the description clearly state what the tool does and how it differs from similar tools?

States a specific verb and resource: "All ECB reference exchange rates for a base currency (default EUR), or only the listed quotes, latest or on a past date." Scope and defaults are clear. However, it never distinguishes itself from sibling tools like fx_history or convert_currency, so an agent must infer which one applies.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Usage Guidelines3/5

Does the description explain when to use this tool, when not to, or what alternatives exist?

Usage is only implied through the default/base/quotes phrasing; there is no explicit "use this when... use fx_history instead when..." guidance. The free-vs-paid tier rules are spelled out, but that is billing guidance rather than tool-selection guidance.

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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