Aether-X Port Congestion
Real-time port congestion risk scores, ETA delays and waiting vessels for 15 global ports
Access real-time and historical data of any and all airborne aircraft.
ADS-B Exchange API is a free Transportation API that requires no API key, is served over HTTPS and has unconfirmed CORS support.
Access ADS-B Exchange data products with live flight APIs and historical datasets, offering high-fidelity, unfiltered aircraft data for research, analytics, and integration.
Details from adsbexchange.com.

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Real-time port congestion risk scores, ETA delays and waiting vessels for 15 global ports
Predictive port congestion, ETA delay and freight volatility signals for 16 global ports
The ADS-B Exchange API is provided by ADS-B (adsbexchange.com). Access ADS-B Exchange data products with live flight APIs and historical datasets, offering high-fidelity, unfiltered aircraft data for research, analytics, and integration.
Yes. The ADS-B Exchange API is listed in the Transportation 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 ADS-B Exchange API requires no authentication, so you can start making requests without signing up.
CORS support for the ADS-B Exchange API is unknown. Test a request from the browser, and fall back to a server-side call if it is blocked.
Yes. The ADS-B Exchange API is served over HTTPS, so it's safe to use in production.