GDPR for APIs: What Developers Need to Know About Privacy by Design

Most GDPR guides are written for marketers and business owners. They talk about cookie banners, privacy policies, and consent management. All useful — but none of it helps you when you're the developer responsible for an API that processes personal data. This guide is for you. We'll cover what GDPR actually requires at the API level, how to implement privacy by design in concrete engineering terms, and the compliance traps that catch developers off guard. APIs Are Data Processors (and Sometimes Controllers) Under GDPR Before diving into implementation, get the legal framing right. Under GDPR, the data controller decides why data is processed. The data processor handles data on behalf of a controller. If your API receives personal data from a client and processes it as instructed, you are likely a data processor. If your API decides what to do with personal data independently, you may be a controller — or a joint controller — for that processing. Why does this matter for developers? Bec