Front Accounting APIs
Front accounting is multilingual and multicurrency software for small businesses

Trading hours and session windows for 65 futures products on 16 global exchanges.
Futures Clock API is a free Finance API that requires no API key, is served over HTTPS and supports CORS, so it can be called from the browser.
How Futures Clock sources, reviews and corrects contract specifications, last-trade dates and first-notice dates, including estimate and freshness rules.
Details from futuresclock.com.

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Front accounting is multilingual and multicurrency software for small businesses
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The Futures Clock API is provided by Futures Clock (futuresclock.com). How Futures Clock sources, reviews and corrects contract specifications, last-trade dates and first-notice dates, including estimate and freshness rules.
Yes. The Futures Clock API is listed in the Finance category of the public-apis directory, which only includes APIs that are free or have a free tier. Check its documentation for rate limits and paid plans.
No. The Futures Clock API requires no authentication, so you can start making requests without signing up.
Yes. The Futures Clock API supports CORS, so front-end JavaScript can call it directly.
Yes. The Futures Clock API is served over HTTPS, so it's safe to use in production.