Debugging and profiling tools

Learn about different tools available to inspect your Expo project at runtime.

React Native consists of both JavaScript and native code. Making this distinction is very important when it comes to debugging. If an error is thrown from the JavaScript code, you might not find it using debugging tools for native code. This page lists a few tools to help you debug your Expo project.

Developer menu

The Developer menu provides access to useful debugging functions. It is built into dev clients and Expo Go. If you are using an emulator, simulator, or have a device connected via USB, you can open this menu by pressing m in the terminal where Expo CLI has started the development server.

Once the Developer menu is open, it will appear as below:

The Developer menu provides the following options:

• Copy link: To copy the dev server address in dev client or exp:// link in Expo of your app.
• Reload: To reload you app. Usually, not necessary since Fast Refresh is enabled by default.
• Go Home: To leave your app and navigate back to the dev client's or Expo Go app's Home screen.
• Toggle performance monitor: To view the performance information about your app.
• Toggle element inspector: To enable or disable the element inspector overlay.
• Open JS debugger: To open React Native DevTools which provides access to Console, Sources, Network (Expo only), Memory, Components, and Profiler, tabs for apps using Hermes. For more information, see the Debugging with React Native DevTools section.
• Fast Refresh: To toggle automatic refreshing of the JS bundle whenever you make changes to files in your project using a text editor.

Now, let's explore some of these options in details.

Toggle performance monitor

Opens up a small overlay that provides the following performance information about your app:

• RAM usage of a project.
• JavaScript heap (this is an easy way to know of any memory leaks in your application).
• Two Views. The top indicates the number of views for the screen and the bottom indicates the number of views in the component.
• Frames Per Second for the UI and JS threads. The UI thread is used for native Android or iOS UI rendering. The JS thread is where most of your logic runs, including API calls, touch events, and so on.

Toggle element inspector

Opens up the element inspector overlay:

This overlay has capabilities to:

• Inspect: Inspect elements
• Perf: Show Performance overlay
• Network: Show network details
• Touchables: Highlight touchable elements

Debugging with React Native DevTools

Starting from React Native 0.76, React Native DevTools has replaced Chrome DevTools.

React Native DevTools is a modern debugging tool for Expo and React Native apps. It allows you to gain insights into the JavaScript code of your app by accessing the Console, Sources, Network (Expo only), and Memory tabs. It also has built-in support for React DevTools such as Components and Profiler tabs. All of these inspectors can be accessed using dev clients or Expo Go.

You can use the React Native DevTools on any app using Hermes. To open it, start your app and press j in the terminal where Expo was started. Once you have opened the React Native DevTools, it will appear as below:

Pausing on breakpoints

You can pause your app on specific parts of your code. To do this, set the breakpoint under the Sources tab by clicking the line number or add the debugger statement in your code.

Once your app is executing code that has a breakpoint, it will entirely pause your app. This allows you to inspect all variables and functions in that scope. You can also execute code in the Console tab as part of your app.

Pausing on exceptions

If your app throws unexpected errors, it can be hard to find the source of the error. You can use React Native DevTools to pause your app and inspect the stack trace and variables the moment it throws an error.

Some errors might be caught by other components in your app, such as Expo Router. In these cases, you can turn on Pause on caught exceptions. It will enable you to inspect any thrown error, even when handled properly.

Interacting with the console

The Console tab gives you access to an interactive terminal, connected directly to your app. You can write any JavaScript inside this terminal to execute snippets of code as if it were part of your app. The code is executed in the global scope by default. But, when using breakpoints from the Sources tab, it executes in the scope of the reached breakpoint. This allows you to invoke methods and access variables throughout your app.

Inspecting network requests (Expo only)

The Network tab in React Native DevTools is only available when you have expo installed in your project.

The Network tab gives you insights into the network requests made by your app. You can inspect each request and response by clicking on them. This includes fetch requests, external loaded media, and in some cases, even requests made by native modules.

See the Inspecting network traffic for alternative ways to inspect network requests.

Inspecting memory

The Memory tab allows you to inspect the memory usage and take a heap snapshot of your app's JavaScript code.

Inspecting components

The Components tab allows you to inspect the React components in your app. You can view the props, and styles of each component by hovering that component in React Native DevTools. This is a great way to debug your app's UI and understand how your components are structured.

Profiling JavaScript performance

Profiles are not yet symbolicated with sourcemaps, and can only be used in debug builds. These limitations will be addressed in upcoming releases.

The Profiler tab allows you to record and analyze the performance of your app's JavaScript. You can start recording, interact with your app, and stop recording to analyze the profile.

To profile the native runtime, use the tools included in Android Studio or Xcode.

Debugging with VS Code

VS Code debugger integration is experimental. For the most stable debugging experience, use the React Native DevTools.

VS Code is a popular code editor, which has a built-in debugger. This debugger uses the same system as the React Native DevTools — the inspector protocol.

You can use this debugger with the Expo Tools VS Code extension. This debugger allows you to set breakpoints, inspect variables, and execute code through the debug console.

To start debugging:

• Connect your app
• Open VS Code command palette (based on your computer, it's either Ctrl + Shift + p or Cmd ⌘ + Shift + p)
• Run the Expo: Debug ... VS Code command.

This will attach VS Code to your running app.

Debugging with React DevTools

React DevTools is a great way to look at your components' props and state. You can open it by pressing Shift + m in the terminal where Expo was started. Once it's open, it will appear as below:

React DevTools can also be paired with the element inspector, allowing you to inspect props, state, and instance properties by tapping components inside your app.

Pressing the shift + m shortcut will also show installed dev tools plugins to provide additional ways to inspect your app.

React Native Debugger

The React Native Debugger requires Remote JS debugging, which has been deprecated since React Native 0.73.

The React Native Debugger is a standalone app that wraps the React DevTools, Redux DevTools, and the React Native DevTools. Unfortunately, it requires the deprecated Remote JS debugging workflow and is incompatible with Hermes.

If you are using Expo SDK 50 or above, you can use the Expo dev tools plugins equivalents to the React Native Debugger:

• React DevTools
• Redux DevTools
• React Native DevTools

If you are using Expo SDK 49 or below, you can use the React Native Debugger. This section provides quick get started instructions. For in-depth information, check its documentation.

You can install it via the release page, or if you're on macOS you can run:

Startup

After firing up React Native Debugger, you'll need to specify the port (shortcuts: Cmd ⌘ + t on macOS, Ctrl + t on Linux/Windows) to 8081. After that, run your project with npx expo start, and select Debug remote JS from the Developer Menu. The debugger should automatically connect.

In the debugger console, you can see the Element tree, as well as the props, state, and children of whatever element you select. You also have the Chrome console on the right, and if you type $r in the console, you will see the breakdown of your selected element.

If you right-click anywhere in the React Native Debugger, you'll get some handy shortcuts to reload your JS, enable/disable the element inspector, network inspector, and to log and clear your AsyncStorage content.

Inspecting network traffic

It's easy to use the React Native Debugger to debug your network request: right-click anywhere in the React Native Debugger and select Enable Network Inspect. This will enable the Network tab and allow you to inspect requests of fetch and XMLHttpRequest.

There are however some limitations, so there are a few other alternatives, all of which require using a proxy:

• Charles Proxy (~$50 USD, our preferred tool)
• Proxyman (Free version available or $49 to $59 USD)
• mitmproxy
• Fiddler

Debugging production apps

In reality, apps often ship with bugs. Implementing a crash and bug reporting system can help you get real-time insights of your production apps. See Using error reporting services for more details.