Examples

Use HTMLRewriter to inject prefetched bootstrap data into an SPA shell, eliminating client-side data fetching on initial load. Works with Workers Static Assets or an externally hosted SPA.

Write custom analytics events to Workers Analytics Engine for high-cardinality, time-series data.

Parse and transform large JSON request and response bodies using streaming.

Shows how to restrict access using the HTTP Basic schema.

Send a request to a remote server, read HTML from the response, and serve that HTML.

Deliver an HTML page from an HTML string directly inside the Worker script.

Return JSON directly from a Worker script, useful for building APIs and middleware.

Verify a signed request using the HMAC and SHA-256 algorithms or return a 403.

Use the OpenAI v4 SDK to stream responses from OpenAI.

Protect against timing attacks by safely comparing values using timingSafeEqual.

Inject Turnstile implicitly into HTML elements using the HTMLRewriter runtime API.

Set up custom domain for Images using a Worker or serve images using a prefix path and Cloudflare registered domain.

Allow a client to request static assets while waiting for the HTML response.

Send Additional Cache Tags using Workers

Access custom Cloudflare properties and control how Cloudflare features are applied to every request.

Send two GET request to two urls and aggregates the responses into one response.

Inspects the incoming request's TLS version and blocks if under TLSv1.2.

Redirect requests to certain URLs based on a mapped object to the request's URL.

Cache POST requests using the Cache API.

Return a response based on the incoming request's URL, HTTP method, User Agent, IP address, ASN or device type.

Given the cookie name, get the value of a cookie. You can also use cookies for A/B testing.

Send a GET request and read in JSON from the response. Use to fetch external data.

Personalize website styling based on localized user time.

Get all geolocation data fields and display them in HTML.

Send a POST request with JSON data. Use to share data with external servers.

Redirect requests from one URL to another or from one set of URLs to another set.

Rewrite URL links in HTML using the HTMLRewriter. This is useful for JAMstack websites.

Set common security headers (X-XSS-Protection, X-Frame-Options, X-Content-Type-Options, Permissions-Policy, Referrer-Policy, Strict-Transport-Security, Content-Security-Policy).

Set multiple Cron Triggers on three different schedules.

Set a Cron Trigger for your Worker.

Use the WebSockets API to communicate in real time with your Cloudflare Workers.

Fetch weather data from an API using the user's geolocation data.

Set up an A/B test by controlling what response is served based on cookies. This version supports passing the request through to test and control on the origin, bypassing random assignment.

Example of how to add, change, or delete headers sent in a request or returned in a response.

Allow or deny a request based on a known pre-shared key in a header. This is not meant to replace the WebCrypto API.

Resolve requests to your domain to a set of proxy third-party origin URLs.

Use the Cache API to store responses in Cloudflare's cache.

Determine how to cache a resource by setting TTLs, custom cache keys, and cache headers in a fetch request.

Add the necessary CORS headers to a third party API response.

Redirect a response based on the country code in the header of a visitor.

Protect sensitive data to prevent data loss, and send alerts to a webhooks server in the event of a data breach.

Send debugging information in an errored response to a logging service.

Block other websites from linking to your content. This is useful for protecting images.

Examine the contents of a Headers object by logging to console with a Map.

Create a modified request with edited properties based off of an incoming request.

Fetch and modify response properties which are immutable by creating a copy first.

Serve an HTML form, then read POST requests. Use also to read JSON or POST data from an incoming request.

Respond to the Worker request with the response from another website (example.com in this example).