Free APIs
Free Space & science APIs
| API | Free tier | Auth | Docs |
|---|---|---|---|
| NASA Open APIs APOD, Mars photos, near-Earth objects, EPIC and more Catch: DEMO_KEY has much lower limits | Free key: 1,000 requests/hour by default | API key | docs |
| Launch Library 2 Rocket launches, agencies and spacecraft Catch: Low hourly limit; Patreon for more | Free: 15 requests/hour without key | No key | docs |
| Open Notify (ISS) ISS position, pass times and people in space Catch: HTTP only | Free, no key | No key · no HTTPS | docs |
| Where the ISS at? Current ISS position and satellite positions Catch: Rate limited | Free; about 1 request/second | No key | docs |
| USGS Earthquake API Real-time and historical earthquake events Catch: Queries returning over 20,000 events are rejected | Free, no key | No key | docs |
| NOAA SWPC Data Service Space weather: solar wind, aurora, Kp index Catch: Public JSON products; no formal SLA | Free, no key | No key | docs |
| NASA Exoplanet Archive API Confirmed exoplanets and stellar data Catch: TAP/ADQL query interface | Free, no key | No key | docs |
| Sunrise-Sunset Sunrise, sunset and twilight times by coordinates Catch: Attribution required | Free, no key | No key | docs |
| arXiv API Search and fetch preprint metadata Catch: Follow the legacy API rate-limit guidance in the terms | Free, no key | No key | docs |
| Crossref REST API Scholarly article, DOI and citation metadata Catch: Add a mailto in requests for the faster polite pool | Free, no key | No key | docs |
| OpenAlex API Open index of scholarly works, authors and institutions Catch: Daily request limits; key recommended | Free; no key for light use, API key for more | No key | docs |
| Semantic Scholar API Paper, author and citation graph data Catch: Unauthenticated use shares a pool and may throttle | Free; API key gives 1 request/second | No key | docs |
| PubChem PUG REST Chemical compounds, substances and bioassays Catch: 5 requests/second, 400 per minute | Free, no key; max 5 requests/second | No key | docs |
| iNaturalist API Nature observations, taxa and places Catch: Hard cap 100/minute; keep under 10,000/day | Free, no key for reads; keep under 60 requests/minute | No key | docs |
FAQ
What is the best free space & science API?+
NASA Open APIs, Launch Library 2, Open Notify (ISS) are good places to start. Compare the free tiers and catches in the table; they differ mostly in limits and whether commercial use is allowed.
Is there a space & science API without an API key?+
Yes: Launch Library 2, Open Notify (ISS), Where the ISS at?, USGS Earthquake API, NOAA SWPC Data Service work without a key.
More free APIs: Weather · Maps & geocoding · Finance & crypto · Currency exchange · AI & ML · Email & messaging · IP & geolocation · News & social · Sports · Movies, TV & anime · Music · Books & reference · Government & open data · Translation & language · Images & media · Fake data & testing · Food & recipes · Transportation · Health · Developer tools · Security · Games & fun