Free FX Rates API for Spreadsheets

No signup. No API key. Just ticker.cool/USD/EUR

Google Sheets

=IMPORTDATA("https://ticker.cool/USD/EUR")

LibreOffice Calc

=WEBSERVICE("https://ticker.cool/USD/EUR")

Microsoft Excel

=WEBSERVICE("https://ticker.cool/USD/EUR")

Endpoints

/USD/EUR US Dollar to Euro
/GBP/USD British Pound to US Dollar
/EUR/JPY Euro to Japanese Yen
/JPY/GBP Japanese Yen to British Pound

Supported Currencies

All 31 currencies from ECB daily rates:
EUR
USD
JPY
BGN
CZK
DKK
GBP
HUF
PLN
RON
SEK
CHF
ISK
NOK
TRY
AUD
BRL
CAD
CNY
HKD
IDR
ILS
INR
KRW
MXN
MYR
NZD
PHP
SGD
THB
ZAR