A web app is a program you use through a web browser instead of installing it on your device. You open an address, sign in, and do real work: write documents, book appointments, manage invoices. Gmail, Google Docs, Canva and online banking are all web apps.
How a web app runs in the browser
A web app has two halves. The frontend is the HTML, CSS and JavaScript the browser downloads and runs, which draws the screens and reacts to clicks. The backend lives on a server: it checks who you are, stores your data in a database and answers requests from the frontend, usually through an API. When you press "Save", the browser sends your changes to the server, which writes them down and confirms.
Because the code is fetched each time you visit, the developer updates the app once on the server and every user gets the new version on their next load. There is no app store review and no "please update" prompt.
Web app or website?
The line is about what visitors do. A bakery's site that lists opening hours and a menu is a website: people mostly read it. Add accounts where customers place pre-orders, see past orders and pick a collection time, and that part has become a web app. Most business sites sit somewhere on this spectrum.
An example: a dog groomer's booking tool
A groomer wants clients to book online. A web app lets a client pick a service, see free slots pulled from the groomer's calendar, enter the dog's name and pay a deposit. The groomer logs into an admin screen on a laptop at the shop or a phone at home and sees the same bookings, because everything is stored on the server rather than on one device.
When your business needs a web app, not just a site
You need a web app when customers or staff must log in, save information or complete a task that depends on stored data. If your goal is to be found and contacted, a normal site is cheaper to build and easier to keep secure. Many owners rent a web app instead of building one: a SaaS booking or invoicing tool often does the job.
Mistakes people make with web apps
- Building custom software for a solved problem. Scheduling, invoicing and newsletters already have mature tools.
- Treating login security as an afterthought. Accounts need hashed passwords, HTTPS and sensible session handling from day one.
- Testing only on a desktop. Many users will open the app on a phone, so forms and tables need to work on small screens.
- Forgetting backups. The database is the business record; losing it is far worse than losing a page design.
Related terms
- Native app: the installed alternative built per platform.
- Progressive web app: a web app that can be installed and work offline.
- Single page application: a common way to structure a web app's frontend.
- SaaS: web apps sold as a subscription.