Best Free APIs for Developers: 8 Practical Choices for Prototypes and Small Apps

Free APIs can help you add real data to a prototype without building every backend service yourself. They are useful for demos, internal tools, learning projects, and small applications, but “free” can mean several different things: no API key, a limited free tier, a non-commercial allowance, or a fake dataset intended only for testing.

This guide focuses on APIs with a practical use case and current first-party documentation. It includes weather, exchange rates, country data, holidays, repository metadata, books, and mock data. Before using any API in a client project, check its current terms, attribution requirements, data license, rate limits, and policy on commercial use.

Quick comparison

API	Useful for	Authentication	Important free-use constraint
Open-Meteo	Weather forecasts and historical weather data	None for the free endpoint	The free API is non-commercial and limited to 10,000 calls per day, 5,000 per hour, and 600 per minute
Frankfurter	Exchange rates and historical currency data	None	No daily or monthly quota, but requests are rate-limited to prevent abuse
REST Countries	Country, currency, language, and flag data	API key for live requests	The Free plan lists 1,000 requests per month and a 20-request-per-10-second throughput ceiling
Nager.Date	Public holidays and business-calendar features	None for the community API	The public API advertises no rate limits; verify its current service terms before high-volume use
GitHub REST API	Public repository, issue, release, and user data	None for public data; a token increases the limit	Unauthenticated requests are limited to 60 per hour per IP; authenticated user requests generally get 5,000 per hour
Open Library	Book search and bibliographic lookup	None	Default requests are limited to 1 per second, or 3 per second when identified; it is not intended as high-traffic commercial infrastructure
JSONPlaceholder	Fake REST data for demos and tests	None	Writes are simulated, not persisted; do not use it as a production data store
DummyJSON	Structured sample data for frontend work	None	It is a fake data service for development, testing, and prototyping, not a source of business data

The table is a starting point rather than a promise of unlimited production capacity. A free plan can change, and a service may apply additional abuse prevention or account rules that are not visible in a short example.

1. Open-Meteo for weather data

Open-Meteo provides forecast, historical weather, marine, air-quality, and geocoding endpoints. It is a convenient choice for a weather widget, outdoor-planning tool, educational project, or prototype because the free forecast endpoint does not require an API key.

The free service has clear boundaries. Open-Meteo's terms of use limit non-commercial use to fewer than 10,000 calls per day, 5,000 per hour, and 600 per minute. The terms also require accepting the CC BY 4.0 license for the data. A website with advertising or subscriptions is treated as commercial use in the examples on the terms page, so use Open-Meteo's commercial pricing instead of assuming that the public endpoint is suitable for a monetized product.

The API accepts coordinates and lets you request only the variables your interface needs:

const endpoint = new URL("https://api.open-meteo.com/v1/forecast");
endpoint.search = new URLSearchParams({
  latitude: "52.52",
  longitude: "13.41",
  current: "temperature_2m,weather_code",
  timezone: "auto",
});

const response = await fetch(endpoint);
if (!response.ok) {
  throw new Error(`Weather request failed: ${response.status}`);
}

const weather = await response.json();
console.log(weather.current);

Cache results for the period your interface can tolerate. A weather dashboard does not need to request the same coordinates every time a visitor refreshes the page.

2. Frankfurter for exchange rates

Frankfurter is a useful choice for price displays, budgeting tools, invoices, and educational currency converters. Its public API requires no API key and provides current and historical rates from central banks and other official sources. The service documents coverage for 206 currencies and data going back to 1948, although the available dates and frequency depend on the underlying provider.

Frankfurter's FAQ says that the public API has no daily or monthly quotas. It still rate-limits requests to prevent abuse, so “no quota” does not mean “send unlimited traffic.” The same documentation says that commercial use is allowed, with the important qualification that you must follow the terms of the underlying data providers. For a compliance-sensitive calculation, request a specific provider rather than treating a blended rate as an accounting or trading source.

The current API documentation uses version 2 endpoints such as the rates endpoint:

async function convert(amount, base, quote) {
  const response = await fetch(
    `https://api.frankfurter.dev/v2/rate/${base}/${quote}`,
  );

  if (!response.ok) {
    throw new Error(`Exchange-rate request failed: ${response.status}`);
  }

  const { rate } = await response.json();
  return (amount * rate).toFixed(2);
}

console.log(await convert(25, "EUR", "USD"));

Do not use a daily reference-rate API for live trading, card authorization, or any workflow that requires intraday quotes. Store the date of the rate used when a conversion affects an invoice or a user-visible financial record.

3. REST Countries for country reference data

REST Countries has moved beyond the old unauthenticated v3.1 endpoints. Its current API family requires an API key for live requests and offers a demo key for testing the documentation. The API provides normalized country information including names, ISO codes, capitals, currencies, languages, flags, borders, time zones, and other fields.

The current documentation lists a Free plan with 1,000 requests per month. It also documents a shared throughput ceiling of 20 requests per 10 seconds. Every API in the account shares the monthly quota, so a small application should cache country records instead of loading the complete country list on every page request.

Use it for country pickers, localized onboarding, timezone hints, flag selectors, and educational interfaces. It is less suitable as the only source for legal, tax, sanctions, or compliance decisions; those fields need a source and review process appropriate to the decision.

Keep the key on a server when possible. If a browser must call the API directly, follow the documentation's browser usage and CORS guidance and restrict the allowed origins. Do not put a production key in a public repository or an unrestricted frontend bundle.

4. Nager.Date for public holidays

Nager.Date provides public-holiday data for more than 200 countries. The community REST API is useful for delivery estimates, booking calendars, staff scheduling, event registration, and small-business opening-hours logic. Its current documentation shows a v4 request such as:

GET https://nagerholidays.com/api/v4/Holidays/US/2026

The service advertises no rate limits and browser-ready CORS support for the public API. That is helpful for a prototype, but your application should still cache a country's holiday list for a year and handle failures. “No rate limits” is not permission to create unnecessary traffic or to assume that an operational guarantee exists.

Holiday data needs interpretation. A national holiday may differ from a regional or local holiday, and some dates depend on later official announcements or lunar observations. Nager's documentation distinguishes holiday types and subdivision codes, but you should confirm important dates with the relevant authority before using them for payroll, legal deadlines, or contractual commitments.

The Nager.Date GitHub repository is MIT licensed, but that license covers the repository's software. Check the API's current service terms and the provenance of the data separately if you are building a commercial calendar product.

5. GitHub REST API for repository data

The GitHub REST API is a practical source for public repository metadata, releases, issues, pull requests, contributors, and user information. It is useful for project dashboards, release notes, changelog pages, dependency reports, and developer portfolio tools.

You can request public data without authentication, but GitHub's rate-limit documentation limits unauthenticated requests to 60 per hour per originating IP address. Authenticated user requests generally have a 5,000-request-per-hour limit. Search endpoints and some other operations have additional restrictions.

For a small dashboard, request only the fields you need, cache responses, and use conditional requests when polling. GitHub specifically recommends avoiding wasteful polling and explains how ETag and Last-Modified headers can reduce the cost of unchanged responses:

const response = await fetch("https://api.github.com/repos/torvalds/linux", {
  headers: {
    Accept: "application/vnd.github+json",
    "X-GitHub-Api-Version": "2022-11-28",
    "User-Agent": "my-small-dashboard",
  },
});

if (!response.ok) {
  throw new Error(`GitHub request failed: ${response.status}`);
}

const repository = await response.json();
console.log(repository.stargazers_count);

If visitors share one server-side IP, unauthenticated traffic can exhaust the limit quickly. Use a server-side token only when your application has a legitimate need, store it as a secret, and follow GitHub's authentication and security guidance. GitHub's terms, endpoint-specific rules, and the licenses of repository content still apply; a public API response is not a blanket license to republish every piece of content.

6. Open Library for book search

Open Library's APIs can power a book search, reading list, library catalog prototype, or ISBN lookup. The search API returns bibliographic records in JSON, and it is available without an API key.

Open Library has unusually important usage guidance for a “free API.” Its documentation says the service is intended for open-source, mission-aligned, human-facing discovery and low-volume real-time lookup. It is not intended to be the data backend for high-traffic commercial infrastructure. The default limit is one request per second. Applications that identify themselves with a User-Agent containing an application name and contact email can receive a three-requests-per-second limit.

Identify your application, cache responses, and use a search request to retrieve several records rather than making hundreds of individual book calls. If you need bulk access, Open Library points developers to its monthly data dumps instead of asking the live API to serve a bulk export.

This makes Open Library a strong choice for a personal reading tool or a low-volume discovery interface, but a poor choice for an unreviewed commercial catalog backend. Read its usage guidelines and licensing information before deciding how to store or redistribute the returned metadata.

7. JSONPlaceholder for REST prototypes

JSONPlaceholder is not a source of real business data. It is a free fake REST API for testing and prototyping, with familiar resources such as posts, comments, albums, photos, todos, and users. It requires no registration and supports common HTTP methods.

Use it when you need to build a frontend against predictable JSON before the real backend exists. It is useful for loading states, pagination layouts, empty states, error handling, and tutorial examples:

const response = await fetch(
  "https://jsonplaceholder.typicode.com/posts?_limit=5",
);

if (!response.ok) {
  throw new Error(`Prototype request failed: ${response.status}`);
}

const posts = await response.json();

The guide explains that create, update, and delete operations are faked rather than persisted. That is an important boundary: a successful POST response does not mean that a record is available to another visitor or still exists after the request. Replace it with a real backend before testing authentication, concurrency, persistence, authorization, or data migrations.

8. DummyJSON for richer frontend fixtures

DummyJSON offers sample products, carts, users, posts, comments, quotes, todos, recipes, and images. It is useful when a UI needs more varied fields than a minimal post-and-user fixture, especially for product cards, filters, pagination, shopping flows, and responsive layouts.

The service is designed for development and prototyping and requires no setup or authentication. Its documentation also includes filtering, pagination, nested resources, delayed responses, and custom responses. Those features make it useful for exercising frontend behavior without writing a temporary backend.

Treat the returned records as fixtures, not production data. Do not use sample users or products to make business decisions, and do not build a customer-facing data dependency around a mock service. If you need a stable test suite, copy a small fixture into your own repository or run a local mock server so your tests do not depend on an external service.

How to choose a free API safely

Compare an API on more than whether the first request returns JSON:

Identify the data owner. Is the service authoritative, an aggregator, a community project, or a fake dataset? The answer affects how much verification your application needs.
Check the access model. No API key is convenient, but a free key may provide better rate limits, usage visibility, and a way to revoke access.
Read the limit and failure behavior. Find the request, burst, pagination, and search limits. Plan for 429, 401, 403, timeouts, malformed data, and provider outages.
Cache responsibly. Cache stable country and holiday data for longer; use shorter freshness windows for weather and exchange rates. Respect the provider's caching and attribution terms.
Separate prototypes from production. JSONPlaceholder and DummyJSON can unblock interface work, while Open-Meteo, Frankfurter, GitHub, and other data APIs still need a production integration plan.
Review commercial terms. Open-Meteo explicitly restricts its free tier to non-commercial use. Open Library excludes high-traffic commercial infrastructure from its intended use. Other services may allow commercial calls but impose quotas, attribution, or provider-specific data terms.
Keep credentials and provider calls on the server. A browser-facing key can be copied, so use origin restrictions where available and proxy sensitive requests through a backend or edge function.

For a broader way to find services beyond this maintained shortlist, see our earlier guide to API directories. Treat older directory entries carefully: an API directory can outlive the service, pricing, or documentation it once listed.

Final recommendations

Choose Open-Meteo for a non-commercial weather prototype when its attribution and request limits fit.
Choose Frankfurter for a lightweight currency converter or historical-rate feature, not live trading.
Choose REST Countries when a small free monthly quota and API key are acceptable.
Choose Nager.Date for cached holiday and scheduling features, with human review for important dates.
Choose GitHub REST for repository-aware developer tools and dashboards, using authentication and conditional requests as usage grows.
Choose Open Library for low-volume, human-facing book discovery rather than a high-traffic commercial catalog.
Choose JSONPlaceholder or DummyJSON when you need predictable fixtures while building a frontend.

The best free API is the one whose data, limits, license, and failure behavior match the job. Start with a small integration, log provider errors, cache what is safe to cache, and keep a replacement path before the API becomes a hidden single point of failure.