diff --git a/packages/core/src/browser/shell/tab-bars.ts b/packages/core/src/browser/shell/tab-bars.ts
index f0237776da929..6d3faade9659c 100644
--- a/packages/core/src/browser/shell/tab-bars.ts
+++ b/packages/core/src/browser/shell/tab-bars.ts
@@ -31,7 +31,7 @@ import { IconThemeService } from '../icon-theme-service';
 import { BreadcrumbsRenderer, BreadcrumbsRendererFactory } from '../breadcrumbs/breadcrumbs-renderer';
 import { NavigatableWidget } from '../navigatable-types';
 import { IDragEvent } from '@phosphor/dragdrop';
-import { PINNED_CLASS } from '../widgets/widget';
+import { LOCKED_CLASS, PINNED_CLASS } from '../widgets/widget';
 import { CorePreferences } from '../core-preferences';
 import { HoverService } from '../hover-service';
 
@@ -178,7 +178,8 @@ export class TabBarRenderer extends TabBar.Renderer {
                 { className: 'theia-tab-icon-label' },
                 this.renderIcon(data, isInSidePanel),
                 this.renderLabel(data, isInSidePanel),
-                this.renderBadge(data, isInSidePanel)
+                this.renderBadge(data, isInSidePanel),
+                this.renderLock(data, isInSidePanel)
             ),
             h.div({
                 className: 'p-TabBar-tabCloseIcon action-label',
@@ -275,6 +276,12 @@ export class TabBarRenderer extends TabBar.Renderer {
             : h.div({ className: 'theia-badge-decorator-horizontal' }, `${limitedBadge}`);
     }
 
+    renderLock(data: SideBarRenderData, isInSidePanel?: boolean): VirtualElement {
+        return !isInSidePanel && data.title.className.includes(LOCKED_CLASS)
+            ? h.div({ className: 'p-TabBar-tabLock' })
+            : h.div({});
+    }
+
     protected readonly decorations = new Map<Title<Widget>, WidgetDecoration.Data[]>();
 
     protected resetDecorations(title?: Title<Widget>): void {
diff --git a/packages/core/src/browser/style/tabs.css b/packages/core/src/browser/style/tabs.css
index cb35d7e7f5990..51150ef36507d 100644
--- a/packages/core/src/browser/style/tabs.css
+++ b/packages/core/src/browser/style/tabs.css
@@ -173,6 +173,18 @@
     background: none;
 }
 
+.p-TabBar-tabLock:after {
+    content: "\ebe7";
+    opacity: 0.75;
+    margin-left: 4px;
+    color: inherit;
+    font-family: codicon;
+    font-size: 16px;
+    font-weight: normal;
+    display: inline-block;
+    vertical-align: top;
+}
+
 /* file icons */
 .p-TabBar[data-orientation='horizontal'] .p-TabBar-tabIcon.file-icon,
 .p-TabBar-tab.p-mod-drag-image .p-TabBar-tabIcon.file-icon {
diff --git a/packages/core/src/browser/widgets/widget.ts b/packages/core/src/browser/widgets/widget.ts
index 5274d0f2386a6..09e920a7cf032 100644
--- a/packages/core/src/browser/widgets/widget.ts
+++ b/packages/core/src/browser/widgets/widget.ts
@@ -53,6 +53,7 @@ export const CODICON_LOADING_CLASSES = codiconArray('loading');
 export const SELECTED_CLASS = 'theia-mod-selected';
 export const FOCUS_CLASS = 'theia-mod-focus';
 export const PINNED_CLASS = 'theia-mod-pinned';
+export const LOCKED_CLASS = 'theia-mod-locked';
 export const DEFAULT_SCROLL_OPTIONS: PerfectScrollbar.Options = {
     suppressScrollX: true,
     minScrollbarLength: 35,
@@ -371,6 +372,12 @@ export function pin(title: Title<Widget>): void {
     }
 }
 
+export function lock(title: Title<Widget>): void {
+    if (!title.className.includes(LOCKED_CLASS)) {
+        title.className += ` ${LOCKED_CLASS}`;
+    }
+}
+
 export function togglePinned(title?: Title<Widget>): void {
     if (title) {
         if (isPinned(title)) {
diff --git a/packages/core/src/common/resource.ts b/packages/core/src/common/resource.ts
index 607697993bea7..4f0586a2e8935 100644
--- a/packages/core/src/common/resource.ts
+++ b/packages/core/src/common/resource.ts
@@ -55,6 +55,7 @@ export interface Resource extends Disposable {
      * Undefined if a resource did not read content yet.
      */
     readonly encoding?: string | undefined;
+    readonly isReadonly?: boolean;
     /**
      * Reads latest content of this resource.
      *
diff --git a/packages/editor/src/browser/editor-widget-factory.ts b/packages/editor/src/browser/editor-widget-factory.ts
index da30689b14bf3..f29daafa4643e 100644
--- a/packages/editor/src/browser/editor-widget-factory.ts
+++ b/packages/editor/src/browser/editor-widget-factory.ts
@@ -16,7 +16,7 @@
 
 import { injectable, inject } from '@theia/core/shared/inversify';
 import URI from '@theia/core/lib/common/uri';
-import { SelectionService } from '@theia/core/lib/common';
+import { nls, SelectionService } from '@theia/core/lib/common';
 import { NavigatableWidgetOptions, WidgetFactory, LabelProvider } from '@theia/core/lib/browser';
 import { EditorWidget } from './editor-widget';
 import { TextEditorProvider } from './editor';
@@ -72,6 +72,10 @@ export class EditorWidgetFactory implements WidgetFactory {
 
     private setLabels(editor: EditorWidget, uri: URI): void {
         editor.title.caption = uri.path.fsPath();
+        if (editor.editor.isReadonly) {
+            // nls-todo: 'Read Only' be available with newer VSCode API
+            editor.title.caption += ` • ${nls.localize('theia/editor/readOnly', 'Read Only')}`;
+        }
         const icon = this.labelProvider.getIcon(uri);
         editor.title.label = this.labelProvider.getName(uri);
         editor.title.iconClass = icon + ' file-icon';
diff --git a/packages/editor/src/browser/editor-widget.ts b/packages/editor/src/browser/editor-widget.ts
index 324e2728f59d0..669dff4b97f44 100644
--- a/packages/editor/src/browser/editor-widget.ts
+++ b/packages/editor/src/browser/editor-widget.ts
@@ -15,7 +15,7 @@
 // *****************************************************************************
 
 import { Disposable, SelectionService, Event, UNTITLED_SCHEME } from '@theia/core/lib/common';
-import { Widget, BaseWidget, Message, Saveable, SaveableSource, Navigatable, StatefulWidget } from '@theia/core/lib/browser';
+import { Widget, BaseWidget, Message, Saveable, SaveableSource, Navigatable, StatefulWidget, lock } from '@theia/core/lib/browser';
 import URI from '@theia/core/lib/common/uri';
 import { TextEditor } from './editor';
 
@@ -27,6 +27,9 @@ export class EditorWidget extends BaseWidget implements SaveableSource, Navigata
     ) {
         super(editor);
         this.addClass('theia-editor');
+        if (editor.isReadonly) {
+            lock(this.title);
+        }
         this.toDispose.push(this.editor);
         this.toDispose.push(this.editor.onSelectionChanged(() => this.setSelection()));
         this.toDispose.push(this.editor.onFocusChanged(() => this.setSelection()));
diff --git a/packages/editor/src/browser/editor.ts b/packages/editor/src/browser/editor.ts
index 95997a05bd2e1..ce0a2ce198257 100644
--- a/packages/editor/src/browser/editor.ts
+++ b/packages/editor/src/browser/editor.ts
@@ -196,6 +196,7 @@ export interface TextEditor extends Disposable, TextEditorSelection, Navigatable
     readonly node: HTMLElement;
 
     readonly uri: URI;
+    readonly isReadonly: boolean;
     readonly document: TextEditorDocument;
     readonly onDocumentContentChanged: Event<TextDocumentChangeEvent>;
 
diff --git a/packages/filesystem/src/browser/file-resource.ts b/packages/filesystem/src/browser/file-resource.ts
index b38fda0fb8e55..2db117ac45113 100644
--- a/packages/filesystem/src/browser/file-resource.ts
+++ b/packages/filesystem/src/browser/file-resource.ts
@@ -40,6 +40,7 @@ export namespace FileResourceVersion {
 }
 
 export interface FileResourceOptions {
+    isReadonly: boolean
     shouldOverwrite: () => Promise<boolean>
     shouldOpenAsText: (error: string) => Promise<boolean>
 }
@@ -60,6 +61,9 @@ export class FileResource implements Resource {
     get encoding(): string | undefined {
         return this._version?.encoding;
     }
+    get isReadonly(): boolean {
+        return this.options.isReadonly || this.fileService.hasCapability(this.uri, FileSystemProviderCapabilities.Readonly);
+    }
 
     constructor(
         readonly uri: URI,
@@ -184,15 +188,7 @@ export class FileResource implements Resource {
         }
     }
 
-    saveContents(content: string, options?: ResourceSaveOptions): Promise<void> {
-        return this.doWrite(content, options);
-    }
-
-    saveStream(content: Readable<string>, options?: ResourceSaveOptions): Promise<void> {
-        return this.doWrite(content, options);
-    }
-
-    protected async doWrite(content: string | Readable<string>, options?: ResourceSaveOptions): Promise<void> {
+    protected doWrite = async (content: string | Readable<string>, options?: ResourceSaveOptions): Promise<void> => {
         const version = options?.version || this._version;
         const current = FileResourceVersion.is(version) ? version : undefined;
         const etag = current?.etag;
@@ -218,14 +214,22 @@ export class FileResource implements Resource {
             }
             throw e;
         }
-    }
+    };
 
+    saveStream?: Resource['saveStream'];
+    saveContents?: Resource['saveContents'];
     saveContentChanges?: Resource['saveContentChanges'];
     protected updateSavingContentChanges(): void {
-        if (this.fileService.hasCapability(this.uri, FileSystemProviderCapabilities.Update)) {
-            this.saveContentChanges = this.doSaveContentChanges;
-        } else {
+        if (this.isReadonly) {
             delete this.saveContentChanges;
+            delete this.saveContents;
+            delete this.saveStream;
+        } else {
+            this.saveContents = this.doWrite;
+            this.saveStream = this.doWrite;
+            if (this.fileService.hasCapability(this.uri, FileSystemProviderCapabilities.Update)) {
+                this.saveContentChanges = this.doSaveContentChanges;
+            }
         }
     }
     protected doSaveContentChanges: Resource['saveContentChanges'] = async (changes, options) => {
@@ -317,6 +321,7 @@ export class FileResourceResolver implements ResourceResolver {
             throw new Error('The given uri is a directory: ' + this.labelProvider.getLongName(uri));
         }
         return new FileResource(uri, this.fileService, {
+            isReadonly: stat?.isReadonly ?? false,
             shouldOverwrite: () => this.shouldOverwrite(uri),
             shouldOpenAsText: error => this.shouldOpenAsText(uri, error)
         });
diff --git a/packages/filesystem/src/browser/file-service.ts b/packages/filesystem/src/browser/file-service.ts
index ffc0100cdf93c..c9c59cbfc78b1 100644
--- a/packages/filesystem/src/browser/file-service.ts
+++ b/packages/filesystem/src/browser/file-service.ts
@@ -426,6 +426,16 @@ export class FileService {
         return !!(provider && (provider.capabilities & capability));
     }
 
+    /**
+     * List the schemes and capabilities for registered file system providers
+     */
+    listCapabilities(): { scheme: string; capabilities: FileSystemProviderCapabilities }[] {
+        return Array.from(this.providers.entries()).map(([scheme, provider]) => ({
+            scheme,
+            capabilities: provider.capabilities
+        }));
+    }
+
     protected async withProvider(resource: URI): Promise<FileSystemProvider> {
         // Assert path is absolute
         if (!resource.path.isAbsolute) {
diff --git a/packages/filesystem/src/common/files.ts b/packages/filesystem/src/common/files.ts
index 2dfed8108bb9c..94d1dc781ead0 100644
--- a/packages/filesystem/src/common/files.ts
+++ b/packages/filesystem/src/common/files.ts
@@ -234,6 +234,11 @@ export interface FileStat extends BaseStat {
      */
     isSymbolicLink: boolean;
 
+    /**
+     * The resource is read only.
+     */
+    isReadonly: boolean;
+
     /**
      * The children of the file stat or undefined if none.
      */
@@ -277,6 +282,7 @@ export namespace FileStat {
             isFile: (stat.type & FileType.File) !== 0,
             isDirectory: (stat.type & FileType.Directory) !== 0,
             isSymbolicLink: (stat.type & FileType.SymbolicLink) !== 0,
+            isReadonly: !!stat.permissions && (stat.permissions & FilePermission.Readonly) !== 0,
             mtime: stat.mtime,
             ctime: stat.ctime,
             size: stat.size,
@@ -485,6 +491,14 @@ export enum FileType {
     SymbolicLink = 64
 }
 
+export enum FilePermission {
+
+    /**
+     * File is readonly.
+     */
+    Readonly = 1
+}
+
 export interface Stat {
     type: FileType;
 
@@ -499,6 +513,8 @@ export interface Stat {
     ctime: number;
 
     size: number;
+
+    permissions?: FilePermission;
 }
 
 export interface WatchOptions {
diff --git a/packages/monaco/src/browser/monaco-editor.ts b/packages/monaco/src/browser/monaco-editor.ts
index 5c28658e28b70..96a7d0a5f53c6 100644
--- a/packages/monaco/src/browser/monaco-editor.ts
+++ b/packages/monaco/src/browser/monaco-editor.ts
@@ -220,6 +220,10 @@ export class MonacoEditor extends MonacoEditorServices implements TextEditor {
         return this.onDocumentContentChangedEmitter.event;
     }
 
+    get isReadonly(): boolean {
+        return this.document.isReadonly();
+    }
+
     get cursor(): Position {
         const { lineNumber, column } = this.editor.getPosition()!;
         return this.m2p.asPosition(lineNumber, column);
diff --git a/packages/plugin-ext/src/common/plugin-api-rpc.ts b/packages/plugin-ext/src/common/plugin-api-rpc.ts
index d35b53d04758f..6f8ec9fd68506 100644
--- a/packages/plugin-ext/src/common/plugin-api-rpc.ts
+++ b/packages/plugin-ext/src/common/plugin-api-rpc.ts
@@ -1835,6 +1835,7 @@ export interface DebugMain {
 }
 
 export interface FileSystemExt {
+    $acceptProviderInfos(scheme: string, capabilities?: files.FileSystemProviderCapabilities): void;
     $stat(handle: number, resource: UriComponents): Promise<files.Stat>;
     $readdir(handle: number, resource: UriComponents): Promise<[string, files.FileType][]>;
     $readFile(handle: number, resource: UriComponents): Promise<BinaryBuffer>;
diff --git a/packages/plugin-ext/src/main/browser/file-system-main-impl.ts b/packages/plugin-ext/src/main/browser/file-system-main-impl.ts
index cebfd8d7e95f9..126cb3f8d06bc 100644
--- a/packages/plugin-ext/src/main/browser/file-system-main-impl.ts
+++ b/packages/plugin-ext/src/main/browser/file-system-main-impl.ts
@@ -27,7 +27,7 @@ import { URI } from '@theia/core/shared/vscode-uri';
 import { interfaces } from '@theia/core/shared/inversify';
 import CoreURI from '@theia/core/lib/common/uri';
 import { BinaryBuffer } from '@theia/core/lib/common/buffer';
-import { Disposable } from '@theia/core/lib/common/disposable';
+import { Disposable, DisposableCollection } from '@theia/core/lib/common/disposable';
 import { Event, Emitter } from '@theia/core/lib/common/event';
 import { MAIN_RPC_CONTEXT, FileSystemMain, FileSystemExt, IFileChangeDto } from '../../common/plugin-api-rpc';
 import { RPCProtocol } from '../../common/rpc-protocol';
@@ -46,15 +46,24 @@ export class FileSystemMainImpl implements FileSystemMain, Disposable {
     private readonly _proxy: FileSystemExt;
     private readonly _fileProvider = new Map<number, RemoteFileSystemProvider>();
     private readonly _fileService: FileService;
+    private readonly _disposables = new DisposableCollection();
 
     constructor(rpc: RPCProtocol, container: interfaces.Container) {
         this._proxy = rpc.getProxy(MAIN_RPC_CONTEXT.FILE_SYSTEM_EXT);
         this._fileService = container.get(FileService);
+
+        for (const { scheme, capabilities } of this._fileService.listCapabilities()) {
+            this._proxy.$acceptProviderInfos(scheme, capabilities);
+        }
+
+        this._disposables.push(this._fileService.onDidChangeFileSystemProviderRegistrations(e => this._proxy.$acceptProviderInfos(e.scheme, e.provider?.capabilities)));
+        this._disposables.push(this._fileService.onDidChangeFileSystemProviderCapabilities(e => this._proxy.$acceptProviderInfos(e.scheme, e.provider.capabilities)));
+        this._disposables.push(Disposable.create(() => this._fileProvider.forEach(value => value.dispose())));
+        this._disposables.push(Disposable.create(() => this._fileProvider.clear()));
     }
 
     dispose(): void {
-        this._fileProvider.forEach(value => value.dispose());
-        this._fileProvider.clear();
+        this._disposables.dispose();
     }
 
     $registerFileSystemProvider(handle: number, scheme: string, capabilities: FileSystemProviderCapabilities): void {
diff --git a/packages/plugin-ext/src/plugin/file-system-ext-impl.ts b/packages/plugin-ext/src/plugin/file-system-ext-impl.ts
index 9d771c00322a4..a335a1f03e794 100644
--- a/packages/plugin-ext/src/plugin/file-system-ext-impl.ts
+++ b/packages/plugin-ext/src/plugin/file-system-ext-impl.ts
@@ -137,7 +137,7 @@ class FsLinkProvider {
 
 class ConsumerFileSystem implements vscode.FileSystem {
 
-    constructor(private _proxy: FileSystemMain) { }
+    constructor(private _proxy: FileSystemMain, private _capabilities: Map<string, number>) { }
 
     stat(uri: vscode.Uri): Promise<vscode.FileStat> {
         return this._proxy.$stat(uri).catch(ConsumerFileSystem._handleError);
@@ -148,7 +148,7 @@ class ConsumerFileSystem implements vscode.FileSystem {
     createDirectory(uri: vscode.Uri): Promise<void> {
         return this._proxy.$mkdir(uri).catch(ConsumerFileSystem._handleError);
     }
-    async readFile(uri: vscode.Uri): Promise<Uint8Array> {
+    readFile(uri: vscode.Uri): Promise<Uint8Array> {
         return this._proxy.$readFile(uri).then(buff => buff.buffer).catch(ConsumerFileSystem._handleError);
     }
     writeFile(uri: vscode.Uri, content: Uint8Array): Promise<void> {
@@ -163,6 +163,13 @@ class ConsumerFileSystem implements vscode.FileSystem {
     copy(source: vscode.Uri, destination: vscode.Uri, options?: { overwrite?: boolean }): Promise<void> {
         return this._proxy.$copy(source, destination, { ...{ overwrite: false }, ...options }).catch(ConsumerFileSystem._handleError);
     }
+    isWritableFileSystem(scheme: string): boolean | undefined {
+        const capabilities = this._capabilities.get(scheme);
+        if (typeof capabilities === 'number') {
+            return (capabilities & files.FileSystemProviderCapabilities.Readonly) === 0;
+        }
+        return undefined;
+    }
     private static _handleError(err: any): never {
         // generic error
         if (!(err instanceof Error)) {
@@ -193,6 +200,7 @@ export class FileSystemExtImpl implements FileSystemExt {
     private readonly _proxy: FileSystemMain;
     private readonly _linkProvider = new FsLinkProvider();
     private readonly _fsProvider = new Map<number, vscode.FileSystemProvider>();
+    private readonly _capabilities = new Map<string, number>();
     private readonly _usedSchemes = new Set<string>();
     private readonly _watches = new Map<number, IDisposable>();
 
@@ -203,7 +211,7 @@ export class FileSystemExtImpl implements FileSystemExt {
 
     constructor(rpc: RPCProtocol, private _extHostLanguageFeatures: LanguagesExtImpl) {
         this._proxy = rpc.getProxy(PLUGIN_RPC_CONTEXT.FILE_SYSTEM_MAIN);
-        this.fileSystem = new ConsumerFileSystem(this._proxy);
+        this.fileSystem = new ConsumerFileSystem(this._proxy, this._capabilities);
 
         // register used schemes
         Object.keys(Schemas).forEach(scheme => this._usedSchemes.add(scheme));
@@ -295,8 +303,16 @@ export class FileSystemExtImpl implements FileSystemExt {
     }
 
     private static _asIStat(stat: vscode.FileStat): files.Stat {
-        const { type, ctime, mtime, size } = stat;
-        return { type, ctime, mtime, size };
+        const { type, ctime, mtime, size, permissions } = stat;
+        return { type, ctime, mtime, size, permissions };
+    }
+
+    $acceptProviderInfos(scheme: string, capabilities?: files.FileSystemProviderCapabilities): void {
+        if (typeof capabilities === 'number') {
+            this._capabilities.set(scheme, capabilities);
+        } else {
+            this._capabilities.delete(scheme);
+        }
     }
 
     $stat(handle: number, resource: UriComponents): Promise<files.Stat> {
diff --git a/packages/plugin-ext/src/plugin/plugin-context.ts b/packages/plugin-ext/src/plugin/plugin-context.ts
index 0fee9f59bec5f..69432c6f3f47d 100644
--- a/packages/plugin-ext/src/plugin/plugin-context.ts
+++ b/packages/plugin-ext/src/plugin/plugin-context.ts
@@ -204,6 +204,7 @@ import { CustomEditorsExtImpl } from './custom-editors';
 import { WebviewViewsExtImpl } from './webview-views';
 import { PluginPackage } from '../common';
 import { Endpoint } from '@theia/core/lib/browser/endpoint';
+import { FilePermission } from '@theia/filesystem/lib/common/files';
 
 export function createAPIFactory(
     rpc: RPCProtocol,
@@ -602,8 +603,8 @@ export function createAPIFactory(
             registerTextDocumentContentProvider(scheme: string, provider: theia.TextDocumentContentProvider): theia.Disposable {
                 return workspaceExt.registerTextDocumentContentProvider(scheme, provider);
             },
-            registerFileSystemProvider(scheme: string, provider: theia.FileSystemProvider): theia.Disposable {
-                return fileSystemExt.registerFileSystemProvider(scheme, provider);
+            registerFileSystemProvider(scheme: string, provider: theia.FileSystemProvider, options?: { isCaseSensitive?: boolean, isReadonly?: boolean }): theia.Disposable {
+                return fileSystemExt.registerFileSystemProvider(scheme, provider, options);
             },
             getWorkspaceFolder(uri: theia.Uri): theia.WorkspaceFolder | undefined {
                 return workspaceExt.getWorkspaceFolder(uri);
@@ -1071,6 +1072,7 @@ export function createAPIFactory(
             WorkspaceEdit,
             SymbolInformation,
             FileType,
+            FilePermission,
             FileChangeType,
             ShellQuoting,
             ShellExecution,
diff --git a/packages/plugin/src/theia.d.ts b/packages/plugin/src/theia.d.ts
index 5d92ddc800d8f..0422b0d005d7f 100644
--- a/packages/plugin/src/theia.d.ts
+++ b/packages/plugin/src/theia.d.ts
@@ -5962,6 +5962,18 @@ export module '@theia/plugin' {
         SymbolicLink = 64
     }
 
+    export enum FilePermission {
+        /**
+         * The file is readonly.
+         *
+         * *Note:* All `FileStat` from a `FileSystemProvider` that is registered with
+         * the option `isReadonly: true` will be implicitly handled as if `FilePermission.Readonly`
+         * is set. As a consequence, it is not possible to have a readonly file system provider
+         * registered where some `FileStat` are not readonly.
+         */
+        Readonly = 1
+    }
+
     /**
      * The `FileStat`-type represents metadata about a file
      */
@@ -5993,6 +6005,12 @@ export module '@theia/plugin' {
          * example.
          */
         size: number;
+        /**
+         * The permissions of the file, e.g. whether the file is readonly.
+         *
+         * *Note:* This value might be a bitmask, e.g. `FilePermission.Readonly | FilePermission.Other`.
+         */
+        permissions?: FilePermission;
     }
 
     /**
@@ -6302,6 +6320,21 @@ export module '@theia/plugin' {
          * @param options Defines if existing files should be overwritten.
          */
         copy(source: Uri, target: Uri, options?: { overwrite?: boolean }): Thenable<void>;
+
+        /**
+         * Check if a given file system supports writing files.
+         *
+         * Keep in mind that just because a file system supports writing, that does
+         * not mean that writes will always succeed. There may be permissions issues
+         * or other errors that prevent writing a file.
+         *
+         * @param scheme The scheme of the filesystem, for example `file` or `git`.
+         *
+         * @return `true` if the file system supports writing, `false` if it does not
+         * support writing (i.e. it is readonly), and `undefined` if the editor does not
+         * know about the filesystem.
+         */
+        isWritableFileSystem(scheme: string): boolean | undefined;
     }
 
     /**
diff --git a/packages/property-view/src/browser/resource-property-view/resource-property-data-service.spec.ts b/packages/property-view/src/browser/resource-property-view/resource-property-data-service.spec.ts
index 8d8f64700cd9a..bd38dcf1c6ec6 100644
--- a/packages/property-view/src/browser/resource-property-view/resource-property-data-service.spec.ts
+++ b/packages/property-view/src/browser/resource-property-view/resource-property-data-service.spec.ts
@@ -39,6 +39,7 @@ const mockFileStat: FileStat = {
     isFile: false,
     isDirectory: true,
     isSymbolicLink: false,
+    isReadonly: false,
     resource: new URI('resource'),
     name: 'name'
 };
diff --git a/packages/workspace/src/browser/workspace-commands.spec.ts b/packages/workspace/src/browser/workspace-commands.spec.ts
index a41e0a0ea4d93..68a369b0bd8bb 100644
--- a/packages/workspace/src/browser/workspace-commands.spec.ts
+++ b/packages/workspace/src/browser/workspace-commands.spec.ts
@@ -48,6 +48,7 @@ describe('workspace-commands', () => {
         isFile: true,
         isDirectory: false,
         isSymbolicLink: false,
+        isReadonly: false,
         resource: new URI('foo/bar'),
         name: 'bar',
     };
@@ -56,6 +57,7 @@ describe('workspace-commands', () => {
         isFile: false,
         isDirectory: true,
         isSymbolicLink: false,
+        isReadonly: false,
         resource: new URI('foo'),
         name: 'foo',
         children: [