CLI

Set up and deploy your first Worker with Wrangler, the Cloudflare Developer Platform CLI.

This guide will instruct you through setting up and deploying your first Worker.

Prerequisites

Sign up for a Cloudflare account ↗.
Install Node.js ↗.

Node.js version manager

Use a Node version manager like Volta ↗ or nvm ↗ to avoid permission issues and change Node.js versions. Wrangler, discussed later in this guide, requires a Node version of 16.17.0 or later.

1. Create a new Worker project

Open a terminal window and run C3 to create your Worker project. C3 (create-cloudflare-cli) ↗ is a command-line tool designed to help you set up and deploy new applications to Cloudflare.

npm create cloudflare@latest -- my-first-worker

yarn create cloudflare@latest my-first-worker

pnpm create cloudflare@latest my-first-worker

For setup, select the following options:

For What would you like to start with?, choose Hello World example.
For Which template would you like to use?, choose Hello World Worker.
For Which language do you want to use?, choose JavaScript.
For Do you want to use git for version control?, choose Yes.
For Do you want to deploy your application?, choose No (we will be making some changes before deploying).

Now, you have a new project set up. Move into that project folder.

cd my-first-worker

What files did C3 create?

In your project directory, C3 will have generated the following:

wrangler.toml: Your Wrangler configuration file.
index.js (in /src): A minimal 'Hello World!' Worker written in ES module syntax.
package.json: A minimal Node dependencies configuration file.
package-lock.json: Refer to npm documentation on package-lock.json ↗.
node_modules: Refer to npm documentation node_modules ↗.

What if I already have a project in a git repository?

In addition to creating new projects from C3 templates, C3 also supports creating new projects from existing Git repositories. To create a new project from an existing Git repository, open your terminal and run:

npm create cloudflare@latest -- --template <SOURCE>

<SOURCE> may be any of the following:

user/repo (GitHub)
git@github.com:user/repo
https://github.com/user/repo
user/repo/some-template (subdirectories)
user/repo#canary (branches)
user/repo#1234abcd (commit hash)
bitbucket:user/repo (Bitbucket)
gitlab:user/repo (GitLab)

Your existing template folder must contain the following files, at a minimum, to meet the requirements for Cloudflare Workers:

package.json
wrangler.toml See sample Wrangler configuration
src/ containing a worker script referenced from wrangler.toml

2. Develop with Wrangler CLI

C3 installs Wrangler, the Workers command-line interface, in Workers projects by default. Wrangler lets you to create, test, and deploy your Workers projects.

After you have created your first Worker, run the wrangler dev command in the project directory to start a local server for developing your Worker. This will allow you to preview your Worker locally during development.

npx wrangler dev

If you have never used Wrangler before, it will open your web browser so you can login to your Cloudflare account.

Go to http://localhost:8787 ↗ to view your Worker.

Browser issues?

If you have issues with this step or you do not have access to a browser interface, refer to the wrangler login documentation.

3. Write code

With your new project generated and running, you can begin to write and edit your code.

Find the src/index.js file. index.js will be populated with the code below:

export default {
  async fetch(request, env, ctx) {
    return new Response("Hello World!");
  },
};

Code explanation

This code block consists of a few different parts.

export default {
  async fetch(request, env, ctx) {
    return new Response("Hello World!");
  },
};

export default is JavaScript syntax required for defining JavaScript modules ↗. Your Worker has to have a default export of an object, with properties corresponding to the events your Worker should handle.

export default {
  async fetch(request, env, ctx) {
    return new Response("Hello World!");
  },
};

This fetch() handler will be called when your Worker receives an HTTP request. You can define additional event handlers in the exported object to respond to different types of events. For example, add a scheduled() handler to respond to Worker invocations via a Cron Trigger.

Additionally, the fetch handler will always be passed three parameters: request, env and context.

export default {
  async fetch(request, env, ctx) {
    return new Response("Hello World!");
  },
};

The Workers runtime expects fetch handlers to return a Response object or a Promise which resolves with a Response object. In this example, you will return a new Response with the string "Hello World!".

Replace the content in your current index.js file with the content below, which changes the text output.

export default {
  async fetch(request, env, ctx) {
    return new Response("Hello Worker!");
  },
};

Then, save the file and reload the page. Your Worker's output will have changed to the new text.

No visible changes?

If the output for your Worker does not change, make sure that:

You saved the changes to index.js.
You have wrangler dev running.
You reloaded your browser.

4. Deploy your project

Deploy your Worker via Wrangler to a *.workers.dev subdomain or a Custom Domain.

npx wrangler deploy

If you have not configured any subdomain or domain, Wrangler will prompt you during the publish process to set one up.

Preview your Worker at <YOUR_WORKER>.<YOUR_SUBDOMAIN>.workers.dev.

Seeing 523 errors?

If you see 523 errors when pushing your *.workers.dev subdomain for the first time, wait a minute or so and the errors will resolve themselves.

Next steps

To do more:

Visit the Cloudflare dashboard ↗ for simpler editing.
Review our Examples and Tutorials for inspiration.
Set up bindings to allow your Worker to interact with other resources and unlock new functionality.
Learn how to test and debug your Workers.
Read about Workers limits and pricing.

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