# How I Built a Client-Side HEIC Converter — No Server Required

Every time someone asked me to "just send the photo as JPG," I died a little inside. iPhones have been saving photos as HEIC since iOS 11, and in 2026, the format mismatch is still a daily pain point for millions of people. Most online converters ask you to upload your personal photos to some random server. I wanted to build something better: a converter that runs entirely in your browser, with zero server involvement. Here's how I built it, what broke along the way, and what I learned about decoding Apple's image format with WebAssembly. Why Client-Side Matters The typical file converter architecture is straightforward: user uploads file, server processes it, server returns the result. It works, but it comes with baggage: Privacy: Your photos hit someone else's machine. For personal photos, that's a hard sell. Server costs: Image processing is CPU-intensive. At scale, you're paying real money for compute. Latency: Upload + process + download vs. just... process. Locally. Offline capab