How to Use Flutter DevTools Effectively

 

Hello everyone. In this article, I have compiled what I know, what I need to know and what I have learned about the Flutter DevTools screen and tabs that I have come across since I started developing projects with Flutter. I hope it will be useful for all of us. Let’s get started.

I use VsCode as my IDE, so I access the DevTools screen from there. If we type DevTools in the Command Palette, we can see that it comes up. Here we can open each tab separately, we can also view them all on the same screen as a web page in the browser, which I prefer this method more. In the same way, we can access it from AndroidStudio in a similar way.

The Web Browser view looks like this:

We can also open DevTools by typing the following commands in the terminal.

flutter pub global activate devtools
flutter run --debug
devtools

Let’s start with a review of DevTools by first finding out what it is.

What is Flutter DevTools?

Flutter DevTools is a development tool used to monitor the performance of the application, detect bugs and optimize it. It has various tabs according to their topics. Below I have prepared a table of which tab is used for what and then I will try to explain each of them in detail.

Flutter DevTools — Connected App

What Does It Do?

This is the main screen showing that DevTools is connected to the Flutter application. When the application is running in debug mode, you can see which analysis tools are active.

Here is what you can do:

• You can check if the connection is active.
• You can navigate to different profiler tabs.
• If the connection is lost, you can restart DevTools and reconnect.

Inspector Tab: Widget Tree and UI Structure

What Does It Do?

This tab allows you to examine the widget tree and visual structure of the app. If you have a design problem or unwanted padding, margin, alignment errors, you can easily fix them here.

Usage Scenarios:

• See which widget is where: Examine the structure in the widget tree to make sure you have selected the right widget.
• Analyze padding, margin and alignment errors: Find elements that are misaligned or shifted on the screen.
• Analyze layout errors: Detect unexpected behavior of widgets like SizedBox, Expanded, Flexible, Align, Positioned.
• Solve layout problems: Understand how elements are positioned inside structures such as Column, Row, Stack.

How to use it:

1. Click on the “Select Widget Mode” button (there is a button at the top of the Inspector tab, you can open it and click on the widgets on the screen to select them directly in the widget tree).
2. Click on the widget you got an error or want to inspect.
3. Examine the details of the widget and the parent-child relationship.
4. Hover over it to see details like padding, margin and alignment.

Solution Suggestions:

• Is there an error with spacing? Check Padding and Margin values.
• Is there unnecessary space inside widgets? Check if there are unnecessary width or height values in the Container.
• Is the widget positioned in the wrong place? Check how widgets like Expanded and Flexible behave.

Tip:

• Do you have a very nested widget tree? Create simpler structures instead of using unnecessary Container, Padding or Column.
• Turn on “Show Guidelines” to understand the order in which widgets are loaded.

Performance Tab: UI Fluency and Jank Problems

What does it do?

This tab helps you analyze your app’s smoothness and jank problems. If your app stutters while scrolling, animations are not smooth or you are experiencing frame drops, you should check here.

Usage Scenarios:

• Monitor the frame per second (FPS) value. It lets you know how smoothly the app is running. If your FPS is consistently below 60, the app is not running smoothly.
• Jank occurs when the app’s FPS (Frames Per Second) drops and usually causes the app to hang. Detect this. Find out which processes are causing frame drops. Optimize heavy processes.
• Examine the UI and Raster Thread. Analyze how long UI operations take to process and which widgets are heavy.

How to use it

1. Open the Performance tab and start using your app.
2. Follow the FPS graph at the top.
3. Open the “Count Widget Builds” option to check which widgets are redrawn too much.
4. After identifying problem areas, make performance improvements.

Solution Suggestions:

• Define frequently redrawn widgets as const. The const keyword ensures that the widget is only built the first time it is created. This prevents the widget from being rebuilt on every redraw and improves performance.
• Run heavy operations in the background (use compute() or Isolate). This allows operations to be performed in the background without tying up the UI thread.
• If you have animations or frequently redrawn widgets, you can use RepaintBoundary to move the widgets to a separate screen layer and redraw only that widget.
• If animations get stuck, use TweenAnimationBuilder or AnimatedBuilder to avoid unnecessary rebuilds.
• If you are working with long lists, you can use ListView.builder to render only the items visible on the screen. This will significantly improve performance.
• Asynchronize time-consuming operations within the application. For example, manage data loading and API calls asynchronously with FutureBuilder or StreamBuilder.
• Be careful when using setState(). Instead of re-rendering the entire widget tree, re-render only the part that has been modified.
• Especially if you are using Riverpod or Provider, you can use ValueListenableBuilder and Consumer to only update specific widgets as data changes.

CPU Profiler Tab (Advanced Performance Analysis — CPU Utilization)

What does it do?

This tab allows you to analyze the CPU usage of your application. It gives you detailed information about which functions are overcommitting and how they are affecting the CPU.

Timeline:

• The Timeline section in CPU Profiler allows us to see which processes are using the CPU and for how long while the application is running. On this timeline, we can examine the timings and durations of each CPU process.
• The CPU Sampling data in the timeline shows which processes are taking up the most CPU.

CPU Sampling:

• CPU sampling records which functions the CPU is running every second. This data allows us to determine how much each function or process block uses the CPU.
• CPU sampling shows performance differences between different parts of the application. Some parts may consume more CPU and this can affect the overall speed of the application.

Flame Graph:

• The flame graph is a visual representation of CPU utilization in the application. High CPU-consuming functions appear as larger blocks, which allows us to easily see which processes are using more resources.
• The Flame Graph also shows how interdependent functions are, so you can analyze which other functions a function depends on and the impact of these relationships on the CPU.
• This graph allows you to quickly identify CPU bottlenecks (functions that run slowly or consume too many resources) in your application.

Call Tree:

• The Call Tree shows the relationships between functions in the application. It shows how one function calls other functions and how it uses the CPU.
• Using the call tree, you can identify the main functions or sub-functions that are overloading the CPU.

Here’s what you can do:

• Analyze which functions consume the most CPU. You can see which parts of your code are running slowly.
• Examine the flame chart. It provides a detailed graph showing the order and duration of function calls.
• Optimize by profiling. You can improve performance by isolating long-running processes.

Memory Tab (Memory Usage and Memory Leaks)

What does it do?

This tab helps you analyze your application’s RAM usage and detect possible memory leaks.

Here is what you can do:

• Monitor memory consumption by taking heap snapshots. You can see which objects are being held in memory and which objects are unnecessarily persistent.
• Analyze Garbage Collector (GC) impact. Dart performs automatic memory management, but here you can check if unnecessary objects are persisting in RAM for too long.
• Analyze object sizes and lifetimes. If too many large objects are kept in memory, you should optimize them.

Tip:

• Don’t forget to dispose() stateful widgets.
• If you are using ChangeNotifier or StreamController, you should turn them off manually (by calling dispose()).

Debugger Tab (Code Debugging)

What does it do?

The Debugger tab is used for debugging, adding breakpoints and analyzing variables. You can stop at a certain point in your code (breakpoint) and analyze variables and UI state.

Here is what you can do:

• Analyze variables and code flow by stopping (breakpoint) at certain points in the code. For example, does the widget update correctly when you press the button?
• Use it to catch exceptions and identify the source of the error. For example, is state management working?
• View error messages in detail and find out which function is causing the error. For example, are you getting an error message related to the UI?

How to use it?

• Add a breakpoint to the relevant line of your code.
• Open the Debugger tab to see what stage the code is in.
• Watch live what data the application is processing and how the state changes.
• Track state changes and widget rebuilds step by step.

Tip:

• You can manually stop certain lines of code by adding debugger().
• You can turn on “Exception Pause” mode to see error messages in detail.
• In VS Code or Android Studio, you can add breakpoints to examine variable values live.

Network Tab (API Calls and HTTP Requests)

What does it do?

This tab helps you analyze the network requests (HTTP calls) made by the application.

Here is what you can do:

• Analyze in detail which API requests take how long.
• Measure response times and optimize unnecessary API calls.
• View which requests failed (status code: 400, 500).
• Validate API data by examining JSON responses and requests.

Tip:

• If you make a lot of API calls, you can reduce the load by using a caching mechanism (Hive, SharedPreferences, SQLite).
• Switch to efficient data querying methods like GraphQL or Firebase Firestore.

Logging Tab (Application Logs and Error Tracking)

What does it do?

It shows the log messages in detail during the running process of the application.

Here is what you can do:

• Detect problems in your code by viewing error messages and stack traces.
• Track details such as API calls, user interactions and system events through logs.
• Make debugging easier by adding custom log messages.

Tip:

• You can use debugPrint() to get more readable logs. If you want to have more detailed information about using debugPrint() instead of print(), you can click the link below.

http://theblankbookofme.blogspot.com/2024/07/print-and-debugprint-in-flutter.html

• Instead, you can use the Logger library to create detailed and colorful log messages.

App Size Tab (App Size Analysis)

What does it do?

This tab helps you analyze the total size of your Flutter application and which files are taking up the most space.

Here’s what you can do:

• Find out which packages and assets are taking up the most space.
• Optimize unnecessarily large code and libraries.
• Analyze the differences between AOT (Ahead of Time) and JIT (Just in Time) builds.

Tip:

• You can run flutter build apk --analyze-size for more detailed analysis.
• Check file sizes after flutter build web for web.

Deep Links Tab (In-App Links and Routing)

What does it do?

This tab allows you to navigate directly to specific pages of the app using deep links.

Here’s what you can do:

• You can run deep link tests to navigate to specific pages within the application.
• You can check URL-based redirect structures (for example with Firebase Dynamic Links).
• Verify integration with libraries like Flutter Navigator or GoRouter.

Tip:

• You can use this tab to test if deep link redirects are working.
• You can add deep link support to your app with systems like Firebase Dynamic Links or App Links.

All in all, Flutter DevTools is a super powerful tool that lets you explore every corner of your app. With Inspector you can catch bugs in the UI, with the Performance tab you can analyze frame rate and render statistics, with CPU Profilers you can see which processes are straining your system, and with AppSize you can check if the app is bloating unnecessarily. By using all these tools effectively, you can make your app faster, more efficient and optimized. Regularly monitoring DevTools will not only fix bugs, but also improve your code quality and user experience. In short, every tab here is a powerful tool at your disposal to make your project better. Let’s keep exploring!

Thank you so much for reading.

If you found it valuable, consider following me for more such content.

Thank you.

Selin.