---
title: Static Site Generation (SSG) and custom 404 pages
description: How to configure a Static Site Generation (SSG) application and custom 404 pages with Workers.
image: https://developers.cloudflare.com/dev-products-preview.png
---
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# Static Site Generation (SSG) and custom 404 pages
Static Site Generation (SSG) applications are web applications which are predominantly 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 ](#tab-panel-9751)
* [ wrangler.toml ](#tab-panel-9752)
JSONC
```
{
"name": "my-worker",
// Set this to today's date
"compatibility_date": "2026-05-08",
"assets": {
"directory": "./dist/",
"not_found_handling": "404-page",
"html_handling": "auto-trailing-slash"
}
}
```
TOML
```
name = "my-worker"
# Set this to today's date
compatibility_date = "2026-05-08"
[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%5Fworker%5Ffirst). 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.
./dist/oauth/callback.html
```
OAuth callback
Loading...
```
* [ JavaScript ](#tab-panel-9753)
* [ TypeScript ](#tab-panel-9754)
./worker/index.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=${sessionId}; HttpOnly; SameSite=Strict; Secure; Path=/; Max-Age=86400`,
},
});
} else {
return Response.json(
{ error: "Invalid OAuth code. Please try again." },
{ status: 400 },
);
}
}
return new Response(null, { status: 404 });
}
}
```
./worker/index.ts
```
import { WorkerEntrypoint } from "cloudflare:workers";
export default class extends WorkerEntrypoint {
async fetch(request: Request) {
const url = new URL(request.url);
if (url.pathname === "/api/oauth/callback") {
const code = url.searchParams.get("code");
const sessionId = await exchangeAuthorizationCodeForAccessAndRefreshTokensAndPersistToDatabaseAndGetSessionId(code);
if (sessionId) {
return new Response(null, {
headers: {
"Set-Cookie": `sessionId=${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
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**
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**
null-body response served" }
404PageServed@{ shape: stadium, label: "**404 Not Found**
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/).
```json
{"@context":"https://schema.org","@type":"BreadcrumbList","itemListElement":[{"@type":"ListItem","position":1,"item":{"@id":"/directory/","name":"Directory"}},{"@type":"ListItem","position":2,"item":{"@id":"/workers/","name":"Workers"}},{"@type":"ListItem","position":3,"item":{"@id":"/workers/static-assets/","name":"Static Assets"}},{"@type":"ListItem","position":4,"item":{"@id":"/workers/static-assets/routing/","name":"Routing"}},{"@type":"ListItem","position":5,"item":{"@id":"/workers/static-assets/routing/static-site-generation/","name":"Static Site Generation (SSG) and custom 404 pages"}}]}
```