Open-Meteo

Open-Meteo is a free, open-source weather API that aggregates numerical weather prediction data from 30+ models run by 15+ national weather services (ECMWF, NOAA GFS, DWD ICON, Meteo-France, JMA, UK Met Office and others) and exposes it through simple HTTP GET requests returning JSON, CSV or XLSX. It was created by Patrick Zippenfenig and is unusual in the weather-API market for being genuinely open: the full server source is on GitHub (~5.7k stars), all data sources are credited, and the raw weather datasets are mirrored on the AWS Open Data registry. The non-commercial tier requires no account or API key, which is the single feature developers cite most when comparing it to OpenWeatherMap or Tomorrow.io. It selects the best high-resolution local model for any given coordinate automatically, blending down to 1-2 km resolution in Central Europe, France, the UK and North America while falling back to 9-11 km global models elsewhere.

The product is aimed at indie developers, hobbyist apps, researchers and data scientists who want clean access to multi-model forecast and reanalysis data (1940-present) without wrangling GRIB/NetCDF files. Its breadth is a real differentiator: beyond standard surface forecasts it ships marine/wave, air-quality-with-pollen, solar radiation (including global tilted irradiance for PV panels), ensemble probabilistic forecasts, seasonal forecasts to 9 months, flood, climate-projection and historical-forecast endpoints, all under one consistent query grammar. Performance is strong for a free service, the vendor cites sub-10ms single-location forecast responses and sub-100ms multi-decade historical queries, helped by a FlatBuffers-based response encoding and Swift backend.

Where it loses: it is model data only, not station observations, so users wanting validated actuals or hyperlocal nowcasting (e.g. radar-based rain-in-the-next-minutes) must look elsewhere, and there is no formal SLA on the free tier. Commercial use legally requires a paid subscription ($29/$99/mo and up), and the free tier's rate limits (600/min, 5k/hour, 10k/day) draw occasional frustration from developers who hit them during bursty workloads. Paid plans add a dedicated endpoint, API key and a 99.9% uptime target, but the absence of a public third-party-audited status/SLA page and the small (effectively single-maintainer) team are the main reliability caveats for production buyers.