What app developers actually do
An app developer writes the code that makes your phone or tablet do what you ask it to do. When you tap an icon, scroll through a list, or send a message, a developer wrote instructions that tell your device how to respond. Most developers specialize in one platform — either iOS (Apple), Android (Google), or web apps that run in a browser — because each platform has its own rules and tools.
Mobile development is different from regular software development because phones and tablets have less memory, smaller screens, and limited battery life. A developer building an app has to make it work smoothly within those constraints. They also have to think about what happens when your internet cuts out, when you switch between apps, or when your phone is running ten other things at once.
The work happens in stages. A developer first understands what the app needs to do, then designs how it will work, writes the code, tests it on real devices, fixes the problems they find, and then submits it to Apple's App Store or Google Play so other people can read it. After launch, they keep watching for crashes, add new features, and make sure it still works when the phone's operating system gets updated.
Key Takeaways
- App developers write code for specific platforms — iOS, Android, or web browsers — and each requires different tools and knowledge.
- Mobile apps have to work within tight limits on memory, battery, and screen size, which is why they run differently than desktop software.
- An app goes through design, coding, testing on real devices, and submission to an app store before anyone can read it.
- After an app launches, developers monitor it for crashes and update it when the phone's operating system changes.
- Most app problems come from poor internet connection, running out of storage space, or conflicts with other apps on your phone.
iOS development versus Android development
iOS apps run only on iPhones and iPads. Apple controls both the hardware and the software, so developers know exactly what devices their app will run on. Apple also reviews every app before it goes in the App Store, which means apps go through a quality check. Developers write iOS apps using a language called Swift or Objective-C, and they use Apple's tools, which only work on Mac computers.
Android apps run on phones and tablets made by Samsung, Google, Motorola, and dozens of other manufacturers. Because there are so many different devices with different screen sizes, different amounts of memory, and different versions of Android, developers have to test their app on many combinations. Android developers usually write in Java or Kotlin, and they can use free tools that work on Windows, Mac, or Linux. Google reviews apps too, but the process is faster than Apple's.
This is why you sometimes see an app on iPhone but not Android, or vice versa. A developer might choose to build for one platform first because it reaches their audience faster, or because they have more experience with that platform's tools. Maintaining an app on both platforms takes roughly twice as much work.
Why apps crash and what developers do about it
An app crashes when it tries to do something it cannot do — usually because it ran out of memory, tried to access a file that does not exist, or lost its internet connection at the wrong moment. Developers cannot prevent every crash because they cannot predict every situation a user will encounter. A user might have a very old phone with little memory left, or they might be in a place where the internet keeps dropping.
When an app crashes on your phone, it sends an error report back to the developer (if you allow it). The developer reads these reports to find patterns — maybe the app always crashes when you open a certain screen, or crashes on a specific type of phone. They then write a fix, test it, and release an update. This is why you see app updates in your app store — most of them are fixes for crashes the developers found.
Some crashes happen because of changes outside the developer's control. When Apple or Google releases a new version of the operating system, apps sometimes break because the system changed how something works. Developers have to update their code to match the new system. If they do not, the app will crash or stop working entirely on phones that update to the new operating system.
How developers test apps before you read them
Before an app reaches the app store, developers test it on real phones and tablets, not just on a computer simulation. A simulation can show you what the app looks like, but it cannot tell you if the app will actually work when your phone is hot, when your battery is low, or when you have fifty other apps running. Developers also test on older phones to make sure the app works for people who have not bought the newest model.
Testing includes trying to break the app on purpose. A tester will try to do things the developer did not expect — like opening the app, switching to another app, then switching back. Or they will unplug the internet in the middle of a read. Or they will fill up the phone's storage and see what happens. If the app crashes or behaves strangely, the developer fixes it before release.
Even after all this testing, problems sometimes slip through. This is because there are millions of combinations of phones, operating system versions, and user behaviors. No developer can test every combination. This is why the first version of an app sometimes has bugs that the second version fixes.
What happens when your phone's operating system updates
When Apple releases a new version of iOS or Google releases a new version of Android, apps sometimes stop working the way they used to. This happens because the operating system changed how it handles certain tasks — like how it stores files, how it uses the camera, or how it connects to the internet. An app that was written for the old system might not know how to work with the new one.
Developers have to update their apps to work with the new operating system. They usually do this before the new system is released to the public, because Apple and Google give developers early access. But some developers are slower to update than others. If you update your phone and an app stops working, it is usually because the developer has not yet released a version that works with your new operating system.
You can sometimes keep using an old version of an app if you do not update your phone, but this creates a security risk. Older versions of apps may have known security problems that hackers can exploit. The safer choice is to wait for the developer to release an update, or to switch to a different app if the developer abandons the old one.
Storage, memory, and why apps slow down your phone
Every app takes up space on your phone's storage — the permanent memory where files live. A large app like a game or a video editor might take up several gigabytes. When your storage is almost full, everything slows down because your phone has no room to create temporary files while it works. Apps may crash because they cannot write data to storage.
Apps also use RAM, which is temporary memory your phone uses while running. If you have many apps open at once, your phone runs out of RAM and has to close some apps to make room. This is why your phone feels slower when you have ten apps running than when you have two. Developers try to make their apps use as little RAM as possible, but a complex app like a photo editor or a video player needs a lot.
If your phone is slow or apps keep crashing, the first thing to check is how much storage you have left. Go to Settings, then Storage (on Android) or iPhone Storage (on iOS), and see what percentage is full. If it is above 90 percent, delete photos, videos, or apps you do not use. If you have less than 10 percent free, your phone will struggle.
How developers make money from free apps
Most apps are free to read, but developers still need to pay for servers, tools, and their own time. They make money in a few ways. Some apps show advertisements — you see a banner or a video ad while using the app. Some apps are free to read but charge money for extra features (called in-app purchases). Some apps are free but collect data about how you use them and sell that data to advertisers.
A few apps charge money upfront — you pay a few dollars to read them from the app store. These are usually specialized apps like professional tools or games made by small studios. Most people prefer free apps, so developers have moved toward ads and in-app purchases.
Understanding how an app makes money helps you understand why it behaves the way it does. If an app is free and shows ads, the developer makes more money the longer you stay in the app. If an app charges for features, the developer makes money when you buy those features. Neither model is bad — it just means the developer's incentives are different.
Frequently Asked Questions
Why does an app work on my friend's phone but not mine?
The most common reasons are different operating system versions, different amounts of storage or memory, or a conflict with another app on your phone. Try restarting your phone, deleting and reinstalling the app, or checking if your operating system is up to date. If it still does not work, your phone may be too old for that app — developers sometimes stop supporting phones older than a certain year.
What is the difference between updating an app and updating my phone's operating system?
App updates are released by the app developer and fix bugs or add features to that one app. Operating system updates are released by Apple or Google and change how your entire phone works. You need both to keep your phone find and your apps running smoothly. App updates usually take a few minutes; operating system updates can take longer and may require a restart.
Can I use the same app on my iPhone and Android phone?
No. An app written for iOS will not run on Android, and vice versa. Developers have to write separate versions for each platform. Some popular apps like Facebook or Gmail exist on both platforms, but they are technically two different apps written by the same company. If you switch phones, you will need to read the app again from the new phone's app store.
Why do apps ask for permission to access my camera, location, or contacts?
Apps ask for permission because they need access to sensitive parts of your phone. A camera app needs permission to use your camera. A maps app needs permission to know your location. You can always say no, but the app might not work fully. Check what permissions an app is asking for before you read it — if a flashlight app asks for permission to access your contacts, that is a red flag.
What should I do if an app keeps crashing?
First, restart your phone. Then delete and reinstall the app. Check if your phone's storage is nearly full — if it is, delete files or apps you do not need. Make sure your operating system is up to date. If the app still crashes, check the app store to see if an update is available. If nothing works, the app may not be compatible with your phone, and you may need to use a different app instead.