OpenWeatherMap API for Browser Extensions: A Practical Guide

If you're building a browser extension that shows weather data, OpenWeatherMap is the go-to choice. Their free tier is genuinely useful, the API is well-documented, and it works well for extensions that call the API on-demand (rather than from a server).

Here's what I learned building Weather & Clock Dashboard for Firefox.

Getting Started: Free Tier Limits

The OpenWeatherMap free tier gives you:

60 calls per minute

1,000,000 calls per month

Access to Current Weather Data API

Access to 5 Day / 3 Hour Forecast API

For a new tab extension, even with 10,000 active users opening 20 tabs per day, you'd need ~200,000 calls per day (~6M/month). With 10-minute caching, that drops to ~600,000/month — comfortably under the free limit.

But here's the thing: every user needs their own API key . You cannot bundle your API key in a browser extension that you distribute publicly.…