A fullstack developer is a developer able to work on both the front-end (the interface) and the back-end (server, API, database) of an application.
In practice, they can ship a feature end to end: the screen, the business logic, the data storage. The most common fullstack stacks pair a front-end framework (React, Vue.js) with a back-end in Node.js, PHP, Python or Java, sometimes with TypeScript on both sides.
In reality, most fullstack developers have a dominant side: they are back-end with some front-end, or the reverse. Being truly expert in both remains rare, especially since the role often includes some infrastructure and deployment work.
The profile is in high demand in young companies, where a small team has to cover everything. As the team grows, roles become more specialized.
Why it matters when hiring
The first question to ask a fullstack developer: which side are you strongest on? An honest answer is a good sign; equally strong on both calls for verification. Hire the dominant side that matches your main risk: an interface-heavy product or a demanding back-end. This profile is ideal at the early stage; later, specialists will complement it.