URL encoding — what it is, when it breaks, and how to fix it

URL encoding bugs are some of the most frustrating to debug because they're invisible. A string looks fine in your code, but by the time it arrives at the server it's been mangled — spaces became + signs, the & that was part of your data got interpreted as a query string separator, or the whole parameter silently disappeared. This guide covers how URL encoding works, where it goes wrong, and the exact functions to use in JavaScript and other languages to handle it correctly every time. What