ATP and WTA tennis since 2007: match results, draws, rankings, head to head, surface Elo and odds.
AcesAPI is a free Sports & Fitness API that requires apiKey authentication, is served over HTTPS and supports CORS, so it can be called from the browser.
Full API reference for AcesAPI. 13 tennis data endpoints with parameters, example requests, and response shapes.
Details from acesapi.com.

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The AcesAPI is provided by AcesAPI (acesapi.com). Full API reference for AcesAPI. 13 tennis data endpoints with parameters, example requests, and response shapes.
Yes. The AcesAPI is listed in the Sports & Fitness 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.
Yes. The AcesAPI uses apiKey authentication, so you need to register for credentials before making requests.
Yes. The AcesAPI supports CORS, so front-end JavaScript can call it directly.
Yes. The AcesAPI is served over HTTPS, so it's safe to use in production.