Creating WebUI Interfaces outside components/

This guide is based on Creating WebUI Interfaces in components.

A WebUI page is made of a Polymer single-page application, which communicates with a C++ UI controller, as explained here.

WebUI pages live in chrome/browser/resources and their native counterpart in chrome/browser/ui/webui/. We will start by creating folders for the new page in chrome/browser/[resources|ui/webui]/hello_world. When creating WebUI resources, follow the Web Development Style Guide.

Making a basic WebUI page

For a sample WebUI page you could start with the following files:


  <meta charset="utf-8">
  <link rel="stylesheet" href="hello_world.css">
  <script type="module" src="hello_world.js"></script>


body {
  margin: 0;


<h1>Hello World</h1>
<div id="example-div">[[message_]]</div>


import './strings.m.js';

import {loadTimeData} from 'chrome://resources/js/load_time_data.m.js';
import {PolymerElement} from 'chrome://resources/polymer/v3_0/polymer/polymer_bundled.min.js';
import {getTemplate} from './app.html.js';

export class HelloWorldAppElement extends PolymerElement {
  static get is() {
    return 'hello-world-app';

  static get template() {
    return getTemplate();

  static get properties() {
    return {
      message_: {
        type: String,
        value: () => loadTimeData.getString('message'),

declare global {
  interface HTMLElementTagNameMap {
    'hello-world-app': HelloWorldAppElement;

customElements.define(, HelloWorldAppElement);

Add a tsconfig_base.json file to configure TypeScript options. Typical options needed by Polymer UIs include:

  • disabling noUncheckedIndexAccess
  • disabling noUnusedLocals: private members from Elements are accessed from their HTML template
  • disabling strictPropertyInitialization: Element properties can be initialized via the property map.


  "extends": "../../../../tools/typescript/tsconfig_base.json",
  "compilerOptions": {
    "noUncheckedIndexedAccess": false,
    "noUnusedLocals": false,
    "strictPropertyInitialization": false

Add a file to get TypeScript compilation and to generate the JS file from which the template will be imported.



build_webui("build") {
  grd_prefix = "hello_world"

  static_files = [ "hello_world.html", "hello_world.css" ]

  web_component_files = [ "app.ts" ]

  non_web_component_files = [
    # For example the BrowserProxy file would go here.

  ts_deps = [

Note: See the build config docs for more examples of how the build could be configured.

Finally, create an OWNERS file for the new folder.

Adding the resources

The build_webui target in autogenerates some targets and files that need to be linked from the binary-wide resource targets:

Add the new resource target to chrome/browser/resources/

group("resources") {
  public_deps += [

Add an entry to resource_ids.spec

This file is for automatically generating resource ids. Ensure that your entry has a unique ID and preserves numerical ordering.


  # START chrome/ WebUI resources section
  ... (lots)
  "<(SHARED_INTERMEDIATE_DIR)/chrome/browser/resources/hello_world/resources.grd": {
    "META": {"sizes": {"includes": [5]}},
    "includes": [2085],

Also add to chrome/chrome_paks.gni

template("chrome_extra_paks") {
  ... (lots)
  sources += [
  deps += [

Adding URL constants for the new chrome URL


const char kChromeUIHelloWorldURL[] = "chrome://hello-world/";
const char kChromeUIHelloWorldHost[] = "hello-world";


extern const char kChromeUIHelloWorldURL[];
extern const char kChromeUIHelloWorldHost[];

Adding a WebUI class for handling requests to the chrome://hello-world/ URL

Next we need a class to handle requests to this new resource URL. Typically this will subclass WebUIController (WebUI dialogs will also need another class which will subclass WebDialogDelegate, this is shown later).



#include "content/public/browser/web_ui_controller.h"

// The WebUI for chrome://hello-world
class HelloWorldUI : public content::WebUIController {
  explicit HelloWorldUI(content::WebUI* web_ui);
  ~HelloWorldUI() override;



#include "chrome/browser/ui/webui/hello_world_ui.h"

#include "chrome/browser/ui/webui/webui_util.h"
#include "chrome/common/webui_url_constants.h"
#include "content/public/browser/browser_context.h"
#include "content/public/browser/web_contents.h"
#include "chrome/grit/hello_world_resources.h"
#include "chrome/grit/hello_world_resources_map.h"
#include "content/public/browser/web_ui.h"
#include "content/public/browser/web_ui_data_source.h"

HelloWorldUI::HelloWorldUI(content::WebUI* web_ui)
    : content::WebUIController(web_ui) {
  // Set up the chrome://hello-world source.
  content::WebUIDataSource* source = content::WebUIDataSource::CreateAndAdd(

  // Add required resources.
      base::make_span(kHelloWorldResources, kHelloWorldResourcesSize),

  // As a demonstration of passing a variable for JS to use we pass in some
  // a simple message.
  source->AddString("message", "Hello World!");

HelloWorldUI::~HelloWorldUI() = default;

To ensure that your code actually gets compiled, you need to add it to chrome/browser/ui/

static_library("ui") {
  sources = [
    ... (lots)

Adding your WebUI request handler to the Chrome WebUI factory

The Chrome WebUI factory is where you setup your new request handler.


+ #include "chrome/browser/ui/webui/hello_world/hello_world_ui.h"
+ if ( == chrome::kChromeUIHelloWorldHost)
+   return &NewWebUI<HelloWorldUI>;

Check everything works

You're done! Assuming no errors (because everyone gets their code perfect the first time) you should be able to compile and run chrome and navigate to chrome://hello-world/ and see your nifty welcome text!

Making a WebUI Dialog

Instead of having a full page for your WebUI, you might want a dialog in order to have a fully independent window. To do that, some small changes are needed to your code. First, we need to add a new class which inherits from ui::WebDialogDelegate. The easiest way to do that is to edit the hello_world_ui.* files


 // Leave the old content, but add this new code
 class HelloWorldDialog : public ui::WebDialogDelegate {
  static void Show();
  ~HelloWorldDialog() override;
  HelloWorldDialog(const HelloWorldDialog&) = delete;
  HelloWorldDialog& operator=(const HelloWorldDialog&) = delete;

  // ui::WebDialogDelegate:
  ui::ModalType GetDialogModalType() const override;
  std::u16string GetDialogTitle() const override;
  GURL GetDialogContentURL() const override;
  void GetWebUIMessageHandlers(
      std::vector<content::WebUIMessageHandler*>* handlers) const override;
  void GetDialogSize(gfx::Size* size) const override;
  std::string GetDialogArgs() const override;
  void OnDialogShown(content::WebUI* webui) override;
  void OnDialogClosed(const std::string& json_retval) override;
  void OnCloseContents(content::WebContents* source,
                       bool* out_close_dialog) override;
  bool ShouldShowDialogTitle() const override;

  content::WebUI* webui_ = nullptr;


 // Leave the old content, but add this new stuff

HelloWorldDialog::HelloWorldDialog() = default;

void HelloWorldDialog::Show() {
  // HelloWorldDialog is self-deleting via OnDialogClosed().
  chrome::ShowWebDialog(nullptr, ProfileManager::GetActiveUserProfile(),
                        new HelloWorldDialog());

ui::ModalType HelloWorldDialog::GetDialogModalType() const {
  return ui::MODAL_TYPE_NONE;

std::u16string HelloWorldDialog::GetDialogTitle() const {
  return u"Hello world";

GURL HelloWorldDialog::GetDialogContentURL() const {
  return GURL(chrome::kChromeUIHelloWorldURL[);

void HelloWorldDialog::GetWebUIMessageHandlers(
    std::vector<content::WebUIMessageHandler*>* handlers) const {}

void HelloWorldDialog::GetDialogSize(gfx::Size* size) const {
  const int kDefaultWidth = 544;
  const int kDefaultHeight = 628;
  size->SetSize(kDefaultWidth, kDefaultHeight);

std::string HelloWorldDialog::GetDialogArgs() const {
  return "";

void HelloWorldDialog::OnDialogShown(content::WebUI* webui) {
  webui_ = webui;

void HelloWorldDialog::OnDialogClosed(const std::string& json_retval) {
  delete this;

void HelloWorldDialog::OnCloseContents(content::WebContents* source,
                                        bool* out_close_dialog) {
  *out_close_dialog = true;

bool HelloWorldDialog::ShouldShowDialogTitle() const {
  return true;

HelloWorldDialog::~HelloWorldDialog() = default;

Finally, you will need to do something to actually show your dialog, which can be done by calling HelloWorldDialog::Show().

More elaborate configurations

Referencing resources from another webui page

There are already mechanisms to make resources available chrome-wide, by publishing them under chrome://resources. If this is not appropriate, there are some ways to serve a file from some other webui page directly through another host.

First, a few explanations. The configuration based on the build_webui() BUILD target as presented above generates a few helpers that hide the complexity of the page's configuration. For example, considering the snippet below:

#include "chrome/grit/hello_world_resources.h"
#include "chrome/grit/hello_world_resources_map.h"

HelloWorldUI::HelloWorldUI(content::WebUI* web_ui)
    : content::WebUIController(web_ui) {
  // ...
      base::make_span(kHelloWorldResources, kHelloWorldResourcesSize),

kHelloWorldResources and kHelloWorldResourcesSize come from from the imported grit-generated files, as configured by the build target, and reference the files listed in it so they can be served out of the given host name. For example, they would contain values like:

const webui::ResourcePath kHelloWorldResources[] = {

Using WebUIDataSource::AddResourcePaths() we can add other resources, looking for the right way to declare them by looking through the generated grit files (e.g. via codesearch), or manual registrations if they exist.

#include "chrome/grit/signin_resources.h"
// ...
HelloWorldUI::HelloWorldUI(content::WebUI* web_ui) {
  // ...
  static constexpr webui::ResourcePath kResources[] = {
      {"signin_shared.css.js", IDR_SIGNIN_SIGNIN_SHARED_CSS_JS},
      {"signin_vars.css.js", IDR_SIGNIN_SIGNIN_VARS_CSS_JS},