Stablecoin Gateways

ECB Currency Exchange Rates

fx_reference_rates

Read-onlyIdempotent

Currency exchange rates from the European Central Bank: euro reference rates for 29 currencies plus EUR (USD, GBP, JPY, CHF, CNY...), latest or any day in the last 90 days, with cross rates for any base and optional amount conversion (e.g. 100 USD to EUR). Use for invoicing, pricing and reporting. Reference rates, not transaction rates. Source: ECB; free at ecb.europa.eu. Signed receipt. Price: $0.001 per call via x402 (USDC on Base or XRP on XRPL). The response includes a provenance block (sg-provenance/1): each fact carries its source, source URL, retrieval time and limits; evidence only, no score, rating or verdict. Example arguments: {"base":"USD","symbols":"EUR,GBP,JPY"}.

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_reference_rates"
  }
}

Input Schema

Name	Required	Description
`base`	No	Base currency (ISO 4217), default EUR
`date`	No	Rate date YYYY-MM-DD within the last 90 days; default latest
`amount`	No	Optional amount to convert
`symbols`	No	Comma-separated ISO 4217 codes; default all

Output Schema

Name	Required	Description	Default
`data`	No	ECB reference rates for the base currency on the rate date, optional converted amounts
`receipt`	No	Ed25519-signed, hash-chained receipt; verify free with the verify_receipt tool or POST /v1/verify-receipt. New receipts carry a signed `evidence` object: service_version, data_timestamp, validation, terms_version, terms_hash, provenance_hash.

Schema Changelog

Changes observed during successful MCP inspections.

Changed1 schema field changedOct 24, 2026

addedOutput schema / properties / data / properties / provenance

Added value: +{
+  "description": "The response includes a `provenance` block (sg-provenance/1): each fact carries its source, source URL, retrieval time and limits; evidence only, no score, rating or verdict."
+}

Changed1 schema field changedOct 24, 2026

changedOutput schema / properties / receipt / description

Previous value: -"Ed25519-signed, hash-chained receipt; verify free with the verify_receipt tool or POST /v1/verify-receipt"New value: +"Ed25519-signed, hash-chained receipt; verify free with the verify_receipt tool or POST /v1/verify-receipt. New receipts carry a signed `evidence` object: service_version, data_timestamp, validation, terms_version, terms_hash, provenance_hash."

Changed1 schema field changedOct 22, 2026

changedOutput schema / (root)

Previous value: -nullNew value: +{
+  "description": "Paid result: { data, receipt }. Unpaid calls return an x402 PaymentRequired object instead (isError: true).",
+  "properties": {
+    "data": {
+      "description": "ECB reference rates for the base currency on the rate date, optional converted amounts",
+      "properties": {
+        "base": {},
+        "cross_rates_derived": {},
+        "note": {},
+        "rate_date": {},
+        "rates": {},
+        "requested_date": {},
+        "source": {},
+        "window": {}
+      }
+    },
+    "receipt": {
+      "description": "Ed25519-signed, hash-chained receipt; verify free with the verify_receipt tool or POST /v1/verify-receipt"
+    }
+  },
+  "type": "object"
+}

First observedOct 22, 2026

TDQS

A4.3/5.0

Behavior5/5

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

Beyond the readOnly/idempotent/openWorld annotations, the description discloses the commercial gating ($0.001 per call via x402 with USDC/Base or XRP/XRPL), a signed receipt, the 90-day data window, and the provenance envelope (sg-provenance/1) with per-fact source URLs and retrieval times. These are exactly the traits an agent cannot learn from structured fields and would otherwise stumble into at call time.

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

Conciseness4/5

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

The purpose, coverage and usage are front-loaded in the first two sentences, and every clause carries information. The provenance/pricing tail is dense and slightly marketing-toned, but it is factual and non-redundant, so it earns its place, just not with maximum economy.

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

Completeness5/5

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

For a read-only, idempotent lookup with a full input schema and an output schema, the description covers what remains: data window, currency universe, default behavior, payment/auth mechanics, provenance semantics and a usage example. An agent has everything needed to call it correctly on the first try.

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

Parameters4/5

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

Schema coverage is 100%, so baseline is 3; the description adds a worked argument example ({"base":"USD","symbols":"EUR,GBP,JPY"}) that demonstrates the comma-separated symbols format and how base interacts with filtering. It does not clarify the semantics of the amount parameter's output shape, but the example goes beyond restating the schema.

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?

The description names a specific verb and resource — ECB euro reference rates for 29 currencies, cross rates for any base, optional amount conversion — and gives concrete examples (USD, GBP, JPY, CHF, CNY). It does not, however, differentiate itself from the sibling fx_convert, which appears to overlap on conversion; the agent must infer the split from 'reference rates, not transaction rates'.

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

Usage Guidelines4/5

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

'Use for invoicing, pricing and reporting' gives clear usage context, and 'Reference rates, not transaction rates' excludes a whole class of use. It stops short of naming the alternative (fx_convert) or stating when to prefer it, so it is strong context without explicit sibling routing.

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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