Currency

currency

Fetch exchange rates and convert money amounts through the free, key-less Frankfurter API (ECB-sourced fiat rates, updated daily ~16:00 CET). Prefer os.http.request GET; if the host allowlist is not null, it must include api.frankfurter.dev.

Fiat only — no crypto, no precious metals on v1. Rates refresh on business days, so weekend/holiday requests return the most recent business-day rate.

Endpoints (v1, stable)

Base URL: https://api.frankfurter.dev/v1

symbols is a comma-separated list of ISO 4217 codes. amount multiplies the returned rate, so amount=100&base=USD&symbols=EUR gives "100 USD in EUR".

Calling convention

Latest rate with os.http.request:

[{ "tool": "os.http.request", "args": { "method": "GET", "url": "https://api.frankfurter.dev/v1/latest?base=USD&symbols=EUR,GBP" } }]

Convert 250 USD to JPY:

[{ "tool": "os.http.request", "args": { "method": "GET", "url": "https://api.frankfurter.dev/v1/latest?base=USD&symbols=JPY&amount=250" } }]

Fallback if os.http.request is unavailable or the host is not allowlisted:

[{ "tool": "os.shell.run", "args": { "cmd": "curl", "args": ["-fsS", "--max-time", "25", "https://api.frankfurter.dev/v1/latest?base=USD&symbols=EUR&amount=100"] } }]

Response shape

{ "amount": 100.0, "base": "USD", "date": "2026-05-29", "rates": { "EUR": 92.13 } }

rates[<symbol>] already reflects amount. Always report the date so the user knows how fresh the quote is.

When to use

• "What's the USD/EUR rate?", "convert 50 GBP to PLN", "rate of X in Y".
• Historical FX on a given date, or a rate trend over a period.

When NOT to use

• Crypto prices (BTC, ETH) — Frankfurter is fiat-only.
• Real-time / intraday tick data — rates are daily reference rates.
• Precious metals (XAU, XAG) — not available on v1.

Rules

1. Echo the date field with every quote; rates are daily, not live.
2. Validate currency codes against /currencies if the user gives an unusual code.
3. For "convert N", pass amount=N rather than multiplying client-side — the API keeps full precision.
4. Unknown currency codes return HTTP 404 / 422; surface a clear "unsupported currency" message instead of the raw error.