OpenWeatherMap

Overview

OpenWeatherMap is one of the most widely used weather APIs. It provides current weather, 5-day/3-hour forecasts, and — on paid tiers — historical weather, minutely precipitation, and air pollution data for any location on earth.

You need a free API key to get started. The free tier covers current weather and the 5-day forecast, which is enough for most hobby and prototype projects.

Quick Start

Get current weather by city name (replace YOUR_API_KEY):

curl "https://api.openweathermap.org/data/2.5/weather?q=London&units=metric&appid=YOUR_API_KEY"

5-day / 3-hour forecast:

curl "https://api.openweathermap.org/data/2.5/forecast?q=London&units=metric&appid=YOUR_API_KEY"

Key parameters:

Note: responses use Kelvin by default — pass units=metric unless you really want Kelvin.

Authentication

• Create a free account at openweathermap.org and generate an API key (takes a couple of minutes to activate after signup).
• Send the key as the appid query parameter on every request.
• Keep the key server-side; never expose it in client-side code.

Rate Limits & Notes

• Free tier: around 1,000 calls/day for current weather + forecast (exact quota on the pricing page).
• Requests over the limit return a 429; the hourly/daily counters reset on a rolling basis.
• Historical, minutely-precipitation and air-pollution endpoints require paid subscriptions.
• Data coverage is global, but update frequency and accuracy vary by region.

FAQ

Is OpenWeatherMap free? There is a free tier (roughly 1,000 calls/day) covering current weather and the 5-day forecast. Higher limits and extra endpoints are paid.

Why is the temperature number so large? OpenWeatherMap returns Kelvin by default — add units=metric for Celsius.

How do I get an API key? Register at openweathermap.org, go to the API keys section, and generate one. Keys usually activate within minutes.

Can I call it from the browser? CORS is not guaranteed — call it from a server or a small proxy to be safe.