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Building Your ApplicationConfiguringDebugging

Debugging

This documentation explains how you can debug your Next.js frontend and backend code with full source maps support using the VS Code debugger, Chrome DevTools, or Firefox DevTools.

Any debugger that can attach to Node.js can also be used to debug a Next.js application. You can find more details in the Node.js Debugging Guide.

Debugging with VS Code

Create a file named .vscode/launch.json at the root of your project with the following content:

launch.json
{
  "version": "0.2.0",
  "configurations": [
    {
      "name": "Next.js: debug server-side",
      "type": "node-terminal",
      "request": "launch",
      "command": "npm run dev"
    },
    {
      "name": "Next.js: debug client-side",
      "type": "chrome",
      "request": "launch",
      "url": "http://localhost:3000"
    },
    {
      "name": "Next.js: debug client-side (Firefox)",
      "type": "firefox",
      "request": "launch",
      "url": "http://localhost:3000",
      "reAttach": true,
      "pathMappings": [
        {
          "url": "webpack://_N_E",
          "path": "${workspaceFolder}"
        }
      ]
    },
    {
      "name": "Next.js: debug full stack",
      "type": "node",
      "request": "launch",
      "program": "${workspaceFolder}/node_modules/.bin/next",
      "runtimeArgs": ["--inspect"],
      "skipFiles": ["<node_internals>/**"],
      "serverReadyAction": {
        "action": "debugWithEdge",
        "killOnServerStop": true,
        "pattern": "- Local:.+(https?://.+)",
        "uriFormat": "%s",
        "webRoot": "${workspaceFolder}"
      }
    }
  ]
}

Note: To use Firefox debugging in VS Code, you'll need to install the Firefox Debugger extension.

npm run dev can be replaced with yarn dev if you're using Yarn or pnpm dev if you're using pnpm.

If you're changing the port number your application starts on, replace the 3000 in http://localhost:3000 with the port you're using instead.

If you're running Next.js from a directory other than root (for example, if you're using Turborepo) then you need to add cwd to the server-side and full stack debugging tasks. For example, "cwd": "${workspaceFolder}/apps/web".

Now go to the Debug panel (Ctrl+Shift+D on Windows/Linux, ⇧+⌘+D on macOS), select a launch configuration, then press F5 or select Debug: Start Debugging from the Command Palette to start your debugging session.

Using the Debugger in Jetbrains WebStorm

Click the drop down menu listing the runtime configuration, and click Edit Configurations.... Create a JavaScript Debug debug configuration with http://localhost:3000 as the URL. Customize to your liking (e.g. Browser for debugging, store as project file), and click OK. Run this debug configuration, and the selected browser should automatically open. At this point, you should have 2 applications in debug mode: the NextJS node application, and the client/browser application.

Debugging with Browser DevTools

Client-side code

Start your development server as usual by running next dev, npm run dev, or yarn dev. Once the server starts, open http://localhost:3000 (or your alternate URL) in your preferred browser.

For Chrome:

  • Open Chrome's Developer Tools (Ctrl+Shift+J on Windows/Linux, ⌥+⌘+I on macOS)
  • Go to the Sources tab

For Firefox:

  • Open Firefox's Developer Tools (Ctrl+Shift+I on Windows/Linux, ⌥+⌘+I on macOS)
  • Go to the Debugger tab

In either browser, any time your client-side code reaches a debugger statement, code execution will pause and that file will appear in the debug area. You can also search for files to set breakpoints manually:

  • In Chrome: Press Ctrl+P on Windows/Linux or ⌘+P on macOS
  • In Firefox: Press Ctrl+P on Windows/Linux or ⌘+P on macOS, or use the file tree in the left panel

Note that when searching, your source files will have paths starting with webpack://_N_E/./.

Server-side code

To debug server-side Next.js code with browser DevTools, you need to pass the --inspect flag to the underlying Node.js process:

Terminal
NODE_OPTIONS='--inspect' next dev

Good to know: Use NODE_OPTIONS='--inspect=0.0.0.0' to allow remote debugging access outside localhost, such as when running the app in a Docker container.

If you're using npm run dev or yarn dev then you should update the dev script on your package.json:

package.json
{
  "scripts": {
    "dev": "NODE_OPTIONS='--inspect' next dev"
  }
}

Launching the Next.js dev server with the --inspect flag will look something like this:

Terminal
Debugger listening on ws://127.0.0.1:9229/0cf90313-350d-4466-a748-cd60f4e47c95
For help, see: https://nodejs.org/en/docs/inspector
ready - started server on 0.0.0.0:3000, url: http://localhost:3000

For Chrome:

  1. Open a new tab and visit chrome://inspect
  2. Look for your Next.js application in the Remote Target section
  3. Click inspect to open a separate DevTools window
  4. Go to the Sources tab

For Firefox:

  1. Open a new tab and visit about:debugging
  2. Click This Firefox in the left sidebar
  3. Under Remote Targets, find your Next.js application
  4. Click Inspect to open the debugger
  5. Go to the Debugger tab

Debugging server-side code works similarly to client-side debugging. When searching for files (Ctrl+P/⌘+P), your source files will have paths starting with webpack://{application-name}/./ (where {application-name} will be replaced with the name of your application according to your package.json file).

Inspect Server Errors with Browser DevTools

When you encounter an error, inspecting the source code can help trace the root cause of errors.

Next.js will display a Node.js logo like a green button on the dev overlay. By clicking that button, the DevTools URL is copied to your clipboard. You can open a new browser tab with that URL to inspect the Next.js server process.

Copy DevTools url example

Debugging on Windows

Windows users may run into an issue when using NODE_OPTIONS='--inspect' as that syntax is not supported on Windows platforms. To get around this, install the cross-env package as a development dependency (-D with npm and yarn) and replace the dev script with the following.

package.json
{
  "scripts": {
    "dev": "cross-env NODE_OPTIONS='--inspect' next dev"
  }
}

cross-env will set the NODE_OPTIONS environment variable regardless of which platform you are on (including Mac, Linux, and Windows) and allow you to debug consistently across devices and operating systems.

Good to know: Ensure Windows Defender is disabled on your machine. This external service will check every file read, which has been reported to greatly increase Fast Refresh time with next dev. This is a known issue, not related to Next.js, but it does affect Next.js development.

More information

To learn more about how to use a JavaScript debugger, take a look at the following documentation: