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20 Free Public APIs for Your Next Side Project

Hand-picked free APIs, many needing no key, for weather, maps, books, space, food, holidays and more, with project ideas.

By the apimark editorial team · Updated 2026-10-31 · 6 min read

Side projects are the best way to learn a new framework, and a real API makes them far more interesting than a to-do list. These are all listed in our API directory, are free to start with, and many need no API key at all. Always read each provider's terms before using one commercially.

No key required

  • Open-Meteo: weather forecasts and history. Idea: a "should I cycle today?" app.
  • National Weather Service: official US alerts. Idea: a severe-weather notifier.
  • REST Countries: flags, currencies, languages. Idea: a geography quiz.
  • Frankfurter: ECB exchange rates. Idea: a travel budget converter.
  • Open Library: books and covers by ISBN. Idea: a barcode-scanning reading log.
  • Nager.Date: public holidays. Idea: a long-weekend finder.
  • MediaWiki API: Wikipedia content. Idea: a "random article of the day" widget.
  • World Bank Indicators: country statistics. Idea: an interactive chart explorer.
  • JSONPlaceholder and httpbin: fake data and request echo for prototyping.
  • Nominatim: geocoding (respect its strict usage policy and cache results).

Free with a key

  • NASA Open APIs: Astronomy Picture of the Day. Idea: a space wallpaper generator.
  • USDA FoodData Central: nutrition facts. Idea: a recipe calorie calculator.
  • TMDB: movies and TV. Idea: a watch-party picker.
  • Unsplash and Pexels: free photos. Idea: a mood-board builder.
  • FRED: economic time series. Idea: an inflation-adjusted price checker.
  • GitHub REST API: repos and contributions. Idea: a developer portfolio generator.
  • Telegram Bot API: bots. Idea: a daily-digest bot combining the APIs above.
  • openFDA: drug and device data. Idea: a recall-alert dashboard.
  • GIPHY: GIFs. Idea: a reaction-GIF search for chat.

Good habits for public APIs

  1. Cache responses and respect rate limits, especially on community-run services.
  2. Send a descriptive User-Agent with contact details when the provider asks for it.
  3. Keep keys out of front-end code; proxy calls through a small serverless function.
  4. Show required attribution (common for maps, photos and open data).