Website Builder: Preview URL Modifier

TL;DR

PreviewUrlModifier is a DI extension point that lets project developers inject custom query parameters into all Website Builder live preview URLs. Register one implementation; it receives the full URL object and can mutate it however it needs — including async operations like fetching a signed token from a remote API.

Implement the Modifier

Import from webiny/admin/website-builder. The single required method is modify(url: URL): Promise<void> — mutate url.searchParams in place, mark the method async when you need to fetch remote values.

import { PreviewUrlModifier } from "webiny/admin/website-builder";

class MyPreviewUrlModifier implements PreviewUrlModifier.Interface {
  async modify(url: URL) {
    url.searchParams.set("my-param", "my-value");
  }
}

export default PreviewUrlModifier.createImplementation({
  implementation: MyPreviewUrlModifier,
  dependencies: []
});

Async example — fetching a signed token:

class SignedTokenModifier implements PreviewUrlModifier.Interface {
  async modify(url: URL) {
    const token = await fetch("/api/preview-token").then(r => r.text());
    url.searchParams.set("token", token);
  }
}

export default PreviewUrlModifier.createImplementation({
  implementation: SignedTokenModifier,
  dependencies: []
});

Register the Feature

// extensions/previewUrlModifier/index.tsx
import React from "react";
import { createFeature, RegisterFeature } from "webiny/admin";
import MyPreviewUrlModifier from "./MyPreviewUrlModifier.js";

const PreviewUrlModifierFeature = createFeature({
  name: "MyApp/PreviewUrlModifier",
  register(container) {
    container.register(MyPreviewUrlModifier);
  }
});

export default () => <RegisterFeature feature={PreviewUrlModifierFeature} />;

// webiny.config.tsx
<Admin.Extension src={"@/extensions/previewUrlModifier/index.tsx"} />

Where It Applies

Surface	Description
Editor iframe	The live-editing iframe in the page editor
Address bar link	The "copy preview link" button in the editor toolbar
Pages list	Preview icon links in the pages list table

Constraints

• One modifier per project. Only the first registered implementation is used.
• Mutate in place. Return value is ignored; mutate the URL object directly.
• No wb.* collisions. Params prefixed wb. are reserved for internal use.

Related Skills

• wb-custom-page-types -- registering custom page types via PageType abstraction
• wb-page-settings -- extending page settings groups and fields