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

Any debugger that can attach to Node.js can also be used to debug a Blitz 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:

  "version": "0.2.0",
  "configurations": [
      "name": "Blitz: debug server-side",
      "type": "node-terminal",
      "request": "launch",
      "command": "npm run dev"
      "name": "Blitz: debug client-side",
      "type": "pwa-chrome",
      "request": "launch",
      "url": "http://localhost:3000"
      "name": "Blitz: debug full stack",
      "type": "node-terminal",
      "request": "launch",
      "command": "npm run dev",
      "console": "integratedTerminal",
      "serverReadyAction": {
        "pattern": "started server on .+, url: (https?://.+)",
        "uriFormat": "%s",
        "action": "debugWithChrome"

npm run dev can be replaced with yarn dev if you're using Yarn, or with blitz dev if you have Blitz installed globally. 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.

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.

Debugging with Chrome DevTools

Client-side code

Start your development server as usual by running blitz dev, npm run dev, or yarn dev. Once the server starts, open http://localhost:3000 (or your alternate URL) in Chrome. Next, open Chrome's Developer Tools (Ctrl+Shift+J on Windows/Linux, ++I on macOS), then go to the Sources tab

Now, 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 press Ctrl+P on Windows/Linux or +P on macOS to search for a file and set breakpoints manually. Note that when searching here, your source files will have paths starting with webpack://_N_E/./.

Server-side code

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

NODE_OPTIONS='--inspect' blitz dev

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

"dev": "NODE_OPTIONS='--inspect' blitz dev"

Launching the Blitz dev server with the --inspect flag will look something like this:

Debugger listening on ws://
For help, see: https://nodejs.org/en/docs/inspector
ready - started server on, url: http://localhost:3000

Be aware that running NODE_OPTIONS='--inspect' npm run dev or NODE_OPTIONS='--inspect' yarn dev won't work. This would try to start multiple debuggers on the same port: one for the npm/yarn process and one for Blitz. You would then get an error like Starting inspector on failed: address already in use in your console.

Once the server starts, open a new tab in Chrome and visit chrome://inspect, where you should see your Blitz application inside the Remote Target section. Click inspect under your application to open a separate DevTools window, then go to the Sources tab.

Debugging server-side code here works much like debugging client-side code with Chrome DevTools, except that when you search for files here with

Ctrl+P or +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).

Debug logging

If you need a more verbose experience on any Blitz module, for debugging purpose, you can enable advanced logging using the DEBUG environment variable.

Blitz internally use debug package.

For example, if you want to enable the REPL logging you can run the console like so :

DEBUG=blitz:repl blitz console

You can also use a wildcard pattern :

DEBUG=blitz:* blitz console

Here are the namespace used by Blitz :

  • blitz:approot
  • blitz:cli
  • blitz:config
  • blitz:errorboundary
  • blitz:generate
  • blitz:generator
  • blitz:installer
  • blitz:manifest
  • blitz:middleware
  • blitz:new
  • blitz:postinstall
  • blitz:repl
  • blitz:rpc
  • blitz:session
  • blitz:utils

Usage in the browser

You can also have this kind of logging for the client-side part of Blitz. To do so simply set the local storage variable debug to blitz:* or any namespace used by Blitz and then refresh the page.

localStorage.debug = 'blitz:*'

Please, be sure that the devtools console has the verbose level enabled.

More information

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

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