Real-time player-props betting odds with graded prop resolution across 13 books.
PropLine API is a free Sports & Fitness API that requires apiKey authentication, is served over HTTPS and has unconfirmed CORS support.
Every prop graded against the real box score — the thing other odds APIs don't do. Real-time lines, cross-book +EV, and webhooks across 59 sports.
Details from prop-line.com.

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Real-time Pinnacle odds for 13 sports — live and prematch over REST, WebSocket and SSE drop alerts
Live scores, play-by-play, schedules and odds for NFL, NBA, MLB, NHL, NCAA and soccer
The PropLine API is provided by PropLine (prop-line.com). Every prop graded against the real box score — the thing other odds APIs don't do. Real-time lines, cross-book +EV, and webhooks across 59 sports.
Yes. The PropLine API 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 PropLine API uses apiKey authentication, so you need to register for credentials before making requests.
CORS support for the PropLine API is unknown. Test a request from the browser, and fall back to a server-side call if it is blocked.
Yes. The PropLine API is served over HTTPS, so it's safe to use in production.