---
title: Static Site Generation (SSG) and custom 404 pages · Cloudflare Workers docs
description: How to configure a Static Site Generation (SSG) application and
  custom 404 pages with Workers.
lastUpdated: 2025-08-22T14:24:45.000Z
chatbotDeprioritize: false
source_url:
  html: https://developers.cloudflare.com/workers/static-assets/routing/static-site-generation/
  md: https://developers.cloudflare.com/workers/static-assets/routing/static-site-generation/index.md
---

Static Site Generation (SSG) applications are web applications which are predominantely built or "prerendered" ahead-of-time. They are often built with a framework such as [Gatsby](https://developers.cloudflare.com/workers/framework-guides/web-apps/more-web-frameworks/gatsby/) or [Docusaurus](https://developers.cloudflare.com/workers/framework-guides/web-apps/more-web-frameworks/docusaurus/). The build process of these frameworks will produce many HTML files and accompanying client-side resources (e.g. JavaScript bundles, CSS stylesheets, images, fonts, etc.). Data is either static, fetched and compiled into the HTML at build-time, or fetched by the client from an API with client-side requests.

Often, an SSG framework will allow you to create a custom 404 page.

## Configuration

In order to deploy a Static Site Generation application to Workers, you must configure the `assets.directory`, and optionally, the `assets.not_found_handling` and `assets.html_handling` options in your [Wrangler configuration file](https://developers.cloudflare.com/workers/wrangler/configuration/#assets):

* wrangler.jsonc

  ```jsonc
  {
    "name": "my-worker",
    "compatibility_date": "2025-11-05",
    "assets": {
      "directory": "./dist/",
      "not_found_handling": "404-page",
      "html_handling": "auto-trailing-slash"
    }
  }
  ```

* wrangler.toml

  ```toml
  name = "my-worker"
  compatibility_date = "2025-11-05"


  [assets]
  directory = "./dist/"
  not_found_handling = "404-page"
  html_handling = "auto-trailing-slash"
  ```

`assets.html_handling` defaults to `auto-trailing-slash` and this will usually give you the desired behavior automatically: individual files (e.g. `foo.html`) will be served *without* a trailing slash and folder index files (e.g. `foo/index.html`) will be served *with* a trailing slash. Alternatively, you can force trailing slashes (`force-trailing-slash`) or drop trailing slashes (`drop-trailing-slash`) on requests for HTML pages.

### Custom 404 pages

Configuring `assets.not_found_handling` to `404-page` overrides the default serving behavior of Workers for static assets. When an incoming request does not match a file in the `assets.directory`, Workers will serve the contents of the nearest `404.html` file with a `404 Not Found` status.

### Navigation requests

If you have a Worker script (`main`), have configured `assets.not_found_handling`, and use the [`assets_navigation_prefers_asset_serving` compatibility flag](https://developers.cloudflare.com/workers/configuration/compatibility-flags/#navigation-requests-prefer-asset-serving) (or set a compatibility date of `2025-04-01` or greater), *navigation requests* will not invoke the Worker script. A *navigation request* is a request made with the `Sec-Fetch-Mode: navigate` header, which browsers automatically attach when navigating to a page. This reduces billable invocations of your Worker script, and is particularly useful for client-heavy applications which would otherwise invoke your Worker script very frequently and unnecessarily.

Note

This can lead to surprising but intentional behavior. For example, if you define an API endpoint in a Worker script (e.g. `/api/date`) and then fetch it with a client-side request in your SPA (e.g. `fetch("/api/date")`), the Worker script will be invoked and your API response will be returned as expected. However, if you navigate to `/api/date` in your browser, you will be served an HTML file. Again, this is to reduce the number of billable invocations for your application while still maintaining SPA-like functionality. This behavior can be disabled by setting the [`assets_navigation_has_no_effect` compatibility flag](https://developers.cloudflare.com/workers/configuration/compatibility-flags/#navigation-requests-prefer-asset-serving).

Note

If you wish to run the Worker script ahead of serving static assets (e.g. to log requests, or perform some authentication checks), you can additionally configure the [`assets.run_worker_first` setting](https://developers.cloudflare.com/workers/static-assets/routing/worker-script/#run_worker_first). This will retain your `assets.not_found_handling` behavior when no other asset matches, while still allowing you to control access to your application with your Worker script.

#### Client-side callbacks

In some cases, you might need to pass a value from a navigation request to your Worker script. For example, if you are acting as an OAuth callback, you might expect to see requests made to some route such as `/oauth/callback?code=...`. With the `assets_navigation_prefers_asset_serving` flag, your HTML assets will be server, rather than your Worker script. In this case, we recommend, either as part of your client application for this appropriate route, or with a slimmed-down endpoint-specific HTML file, passing the value to the server with client-side JavaScript.

```html
<!DOCTYPE html>
<html>
  <head>
    <title>OAuth callback</title>
  </head>
  <body>
    <p>Loading...</p>
    <script>
      (async () => {
        const response = await fetch("/api/oauth/callback" + window.location.search);
        if (response.ok) {
          window.location.href = '/';
        } else {
          document.querySelector('p').textContent = 'Error: ' + (await response.json()).error;
        }
      })();
    </script>
  </body>
</html>
```

* JavaScript

  ```js
  import { WorkerEntrypoint } from "cloudflare:workers";


  export default class extends WorkerEntrypoint {
    async fetch(request) {
      const url = new URL(request.url);
      if (url.pathname === "/api/oauth/callback") {
        const code = url.searchParams.get("code");


        const sessionId =
          await exchangeAuthorizationCodeForAccessAndRefreshTokensAndPersistToDatabaseAndGetSessionId(
            code,
          );


        if (sessionId) {
          return new Response(null, {
            headers: {
              "Set-Cookie": `sessionId=${sessionId}; HttpOnly; SameSite=Strict; Secure; Path=/; Max-Age=86400`,
            },
          });
        } else {
          return Response.json(
            { error: "Invalid OAuth code. Please try again." },
            { status: 400 },
          );
        }
      }


      return new Response(null, { status: 404 });
    }
  }
  ```

* TypeScript

  ```ts
  import { WorkerEntrypoint } from "cloudflare:workers";


  export default class extends WorkerEntrypoint {
    async fetch(request: Request) {
      const url = new URL(request.url);
      if (url.pathname === "/api/oauth/callback") {
        const code = url.searchParams.get("code");


        const sessionId = await exchangeAuthorizationCodeForAccessAndRefreshTokensAndPersistToDatabaseAndGetSessionId(code);


        if (sessionId) {
          return new Response(null, {
            headers: {
              "Set-Cookie": `sessionId=${sessionId}; HttpOnly; SameSite=Strict; Secure; Path=/; Max-Age=86400`,
            },
          });
        } else {
          return Response.json(
            { error: "Invalid OAuth code. Please try again." },
            { status: 400 }
          );
        }
      }


      return new Response(null, { status: 404 });
    }
  }
  ```

## Local Development

If you are using a Vite-powered SPA framework, you might be interested in using our [Vite plugin](https://developers.cloudflare.com/workers/vite-plugin/) which offers a Vite-native developer experience.

### Reference

In most cases, configuring `assets.not_found_handling` to `404-page` will provide the desired behavior. If you are building your own framework, or have specialized needs, the following diagram can provide insight into exactly how the routing decisions are made.

Full routing decision diagram

```mermaid
flowchart
Request@{ shape: stadium, label: "Incoming request" }
Request-->RunWorkerFirst
RunWorkerFirst@{ shape: diamond, label: "Run Worker script first?" }
RunWorkerFirst-->|Request matches run_worker_first path|WorkerScriptInvoked
RunWorkerFirst-->|Request matches run_worker_first negative path|AssetServing
RunWorkerFirst-->|No matches|RequestMatchesAsset
RequestMatchesAsset@{ shape: diamond, label: "Request matches asset?" }
RequestMatchesAsset-->|Yes|AssetServing
RequestMatchesAsset-->|No|WorkerScriptPresent
WorkerScriptPresent@{ shape: diamond, label: "Worker script present?" }
WorkerScriptPresent-->|No|AssetServing
WorkerScriptPresent-->|Yes|RequestNavigation
RequestNavigation@{ shape: diamond, label: "Request is navigation request?" }
RequestNavigation-->|No|WorkerScriptInvoked
WorkerScriptInvoked@{ shape: rect, label: "Worker script invoked" }
WorkerScriptInvoked-.->|Asset binding|AssetServing
RequestNavigation-->|Yes|AssetServing

subgraph Asset serving
	AssetServing@{ shape: diamond, label: "Request matches asset?" }
	AssetServing-->|Yes|AssetServed
	AssetServed@{ shape: stadium, label: "**200 OK**<br />asset served" }
	AssetServing-->|No|NotFoundHandling

	subgraph 404-page
		NotFoundHandling@{ shape: rect, label: "Request rewritten to ../404.html" }
		NotFoundHandling-->404PageExists
		404PageExists@{ shape: diamond, label: "HTML Page exists?" }
		404PageExists-->|Yes|404PageServed
		404PageExists-->|No|404PageAtIndex
		404PageAtIndex@{ shape: diamond, label: "Request is for root /404.html?" }
		404PageAtIndex-->|Yes|Generic404PageServed
		404PageAtIndex-->|No|NotFoundHandling
		Generic404PageServed@{ shape: stadium, label: "**404 Not Found**<br />null-body response served" }
		404PageServed@{ shape: stadium, label: "**404 Not Found**<br />404.html page served" }
	end

end
```

Requests are only billable if a Worker script is invoked. From there, it is possible to serve assets using the assets binding (depicted as the dotted line in the diagram above).

You can read more about how we match assets in the [HTML handling docs](https://developers.cloudflare.com/workers/static-assets/routing/advanced/html-handling/).
