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Local development

Cloudflare Workers and most connected resources can be fully developed and tested locally - providing confidence that the applications you build locally will work the same way in production. This allows you to be more efficient and effective by providing a faster feedback loop and removing the need to test against remote resources. Local development runs against the same production runtime used by Cloudflare Workers, workerd.

In addition to testing Workers locally with wrangler dev, the use of Miniflare allows you to test other Developer Platform products locally, such as R2, KV, D1, and Durable Objects.

​​ Start a local development server

Wrangler provides a dev command that starts a local server for developing your Worker. Make sure you have npm installed and run the following in the folder containing your Worker application:

$ npx wrangler dev

wrangler dev will run the preview of the Worker directly on your local machine. wrangler dev uses a combination of workerd and Miniflare, a simulator that allows you to test your Worker against additional resources like KV, Durable Objects, WebSockets, and more.

Resources such as KV, Durable Objects, D1, and R2 will be stored and persisted locally and not affect live production or preview data. Wrangler will automatically create local versions of bindings found in wrangler.toml. These will not have data in them initially, so you will need to add data manually.

​​ Supported resource bindings in local development

Durable Objects
Service Bindings (multiple workers)

​​ Clear Wrangler’s local storage

Wrangler will store all locally created resources and storage in a .wrangler folder inside your Worker directory. This folder should be added to your .gitignore file.

If you need to clear local storage, delete the .wrangler/state folder. It will be recreated the next time you run wrangler dev.

​​ Develop locally using remote resources and bindings

wrangler dev runs locally by default. This means that all resources and bindings are simulated locally as well. However, there may be times you need to develop against remote resources and bindings. To run wrangler dev remotely, add the --remote flag:

$ npx wrangler dev --remote

Remote resources to use during wrangler dev --remote are specified with preview ID/names such as preview_id or preview_bucket name. Preview resources can be resources separate from production resources to prevent changing production data in development. wrangler dev --remote only supports preview ID/names for storage resources such as KV, R2, and D1. To change production data in wrangler dev --remote, set the preview ID/name of the resource to the ID/name of the production resource.

​​ Customize wrangler dev

You can customize how wrangler dev works to fit your needs. Refer to the wrangler dev documentation for available configuration options.

  • Debugging tools - Tools to help you diagnose issues and gain insight into your Workers.

  1. Using Workers AI always accesses your Cloudflare account in order to run AI models and will incur usage charges even in local development. ↩︎