Debugging tools

Being able to assess how your Workers are functioning at various points in the development cycle is vital to identifying the root causes of bugs or issues.

Cloudflare provides a variety of tools to help you debug your Workers.

​​ Chrome DevTools

Wrangler supports using Chrome DevTools Open external link to view logs/sources, set breakpoints, and profile CPU/memory usage. To open a DevTools session connected to your Worker from any Chromium-based browser, run wrangler dev and press the d key in your terminal.

​​ Debug via breakpoints

As of Wrangler 3.9.0, you can debug via breakpoints in your Worker. Breakpoints provide the ability to review what is happening at a given point in the execution of your Worker. Breakpoint functionality exists in both DevTools and VS Code.

For more information on breakpoint debugging via Chrome’s DevTools, refer to Chrome’s article on breakpoints Open external link .

​​ Setup VS Code to use breakpoints

To setup VS Code for breakpoint debugging in your Worker project:

1. Create a .vscode folder in your project’s root folder if one does not exist.
2. Within that folder, create a launch.json file with the following content:

{
  "configurations": [
      {
          "name": "Wrangler",
          "type": "node",
          "request": "attach",
          "port": 9229,
          "cwd": "/",
          "resolveSourceMapLocations": null,
          "attachExistingChildren": false,
          "autoAttachChildProcesses": false,
          "sourceMaps": true // works with or without this line
      }
  ]
}

3. Open your project in VS Code, open a new terminal window from VS Code, and run npx wrangler dev to start the local dev server.

4. At the top of the Run & Debug panel, you should see an option to select a configuration. Choose Wrangler, and select the play icon. Wrangler: Remote Process [0] should show up in the Call Stack panel on the left.

5. Go back to a .js or .ts file in your project and add at least one breakpoint.

6. Open your browser and go to the Worker’s local URL (default http://127.0.0.1:8787). The breakpoint should be hit, and you should be able to review details about your code at the specified line.

​​ Related resources

• Local Development - Develop your Workers and connected resources locally via Wrangler and workerd Open external link , for a fast, accurate feedback loop.