diff --git a/packages/markers/src/browser/problem/problem-widget.tsx b/packages/markers/src/browser/problem/problem-widget.tsx
index c00b32ced6bf3..4ed13eddc4382 100644
--- a/packages/markers/src/browser/problem/problem-widget.tsx
+++ b/packages/markers/src/browser/problem/problem-widget.tsx
@@ -104,7 +104,7 @@ export class ProblemWidget extends TreeWidget {
                     <i className={severityClass}></i>
                 </div>
                 <div className='owner'>
-                    {'[' + problemMarker.owner + ']'}
+                    {'[' + (problemMarker.data.source || problemMarker.owner) + ']'}
                 </div>
                 <div className='message'>{problemMarker.data.message}
                     {
diff --git a/packages/plugin-ext/package.json b/packages/plugin-ext/package.json
index 804c7da56dfa4..923ccb1558dc2 100644
--- a/packages/plugin-ext/package.json
+++ b/packages/plugin-ext/package.json
@@ -10,6 +10,7 @@
     "@theia/editor": "^0.3.19",
     "@theia/file-search": "^0.3.19",
     "@theia/filesystem": "^0.3.19",
+    "@theia/markers": "^0.3.19",
     "@theia/messages": "^0.3.19",
     "@theia/monaco": "^0.3.19",
     "@theia/navigator": "^0.3.19",
diff --git a/packages/plugin-ext/src/api/model.ts b/packages/plugin-ext/src/api/model.ts
index 0f958ed306b88..0d4f64c88f81f 100644
--- a/packages/plugin-ext/src/api/model.ts
+++ b/packages/plugin-ext/src/api/model.ts
@@ -197,7 +197,7 @@ export interface MarkerData {
 }
 
 export interface RelatedInformation {
-    resource: UriComponents;
+    resource: string;
     message: string;
     startLineNumber: number;
     startColumn: number;
diff --git a/packages/plugin-ext/src/api/plugin-api.ts b/packages/plugin-ext/src/api/plugin-api.ts
index af739b9979f9c..3665643acc762 100644
--- a/packages/plugin-ext/src/api/plugin-api.ts
+++ b/packages/plugin-ext/src/api/plugin-api.ts
@@ -900,7 +900,7 @@ export interface LanguagesMain {
     $registerDocumentHighlightProvider(handle: number, selector: SerializedDocumentFilter[]): void;
     $registerQuickFixProvider(handle: number, selector: SerializedDocumentFilter[], codeActionKinds?: string[]): void;
     $clearDiagnostics(id: string): void;
-    $changeDiagnostics(id: string, delta: [UriComponents, MarkerData[]][]): void;
+    $changeDiagnostics(id: string, delta: [string, MarkerData[]][]): void;
     $registerDocumentFormattingSupport(handle: number, selector: SerializedDocumentFilter[]): void;
     $registerRangeFormattingProvider(handle: number, selector: SerializedDocumentFilter[]): void;
     $registerOnTypeFormattingProvider(handle: number, selector: SerializedDocumentFilter[], autoFormatTriggerCharacters: string[]): void;
diff --git a/packages/plugin-ext/src/main/browser/languages-main.ts b/packages/plugin-ext/src/main/browser/languages-main.ts
index 86396760d02dd..75127997662c9 100644
--- a/packages/plugin-ext/src/main/browser/languages-main.ts
+++ b/packages/plugin-ext/src/main/browser/languages-main.ts
@@ -27,25 +27,29 @@ import {
     ResourceFileEditDto,
 } from '../../api/plugin-api';
 import { interfaces } from 'inversify';
-import { SerializedDocumentFilter, MarkerData, Range, WorkspaceSymbolProvider } from '../../api/model';
+import { SerializedDocumentFilter, MarkerData, Range, WorkspaceSymbolProvider, RelatedInformation, MarkerSeverity } from '../../api/model';
 import { RPCProtocol } from '../../api/rpc-protocol';
 import { fromLanguageSelector } from '../../plugin/type-converters';
-import { UriComponents } from '../../common/uri-components';
 import { LanguageSelector } from '../../plugin/languages';
 import { DocumentFilter, MonacoModelIdentifier, testGlob, getLanguages } from 'monaco-languageclient/lib';
 import { DisposableCollection, Emitter } from '@theia/core';
 import { MonacoLanguages } from '@theia/monaco/lib/browser/monaco-languages';
 import URI from 'vscode-uri/lib/umd';
+import CoreURI from '@theia/core/lib/common/uri';
+import { ProblemManager } from '@theia/markers/lib/browser';
+import * as vst from 'vscode-languageserver-types';
 
 export class LanguagesMainImpl implements LanguagesMain {
 
     private ml: MonacoLanguages;
+    private problemManager: ProblemManager;
 
     private readonly proxy: LanguagesExt;
     private readonly disposables = new Map<number, monaco.IDisposable>();
     constructor(rpc: RPCProtocol, container: interfaces.Container) {
         this.proxy = rpc.getProxy(MAIN_RPC_CONTEXT.LANGUAGES_EXT);
         this.ml = container.get(MonacoLanguages);
+        this.problemManager = container.get(ProblemManager);
     }
 
     $getLanguages(): Promise<string[]> {
@@ -158,24 +162,15 @@ export class LanguagesMainImpl implements LanguagesMain {
     }
 
     $clearDiagnostics(id: string): void {
-        const markers = monaco.editor.getModelMarkers({ owner: id });
-        const clearedEditors = new Set<string>(); // uri to resource
-        for (const marker of markers) {
-            const uri = marker.resource;
-            const uriString = uri.toString();
-            if (!clearedEditors.has(uriString)) {
-                const textModel = monaco.editor.getModel(uri);
-                monaco.editor.setModelMarkers(textModel, id, []);
-                clearedEditors.add(uriString);
-            }
+        for (const uri of this.problemManager.getUris()) {
+            this.problemManager.setMarkers(new CoreURI(uri), id, []);
         }
     }
 
-    $changeDiagnostics(id: string, delta: [UriComponents, MarkerData[]][]): void {
-        for (const [uriComponents, markers] of delta) {
-            const uri = monaco.Uri.revive(uriComponents);
-            const textModel = monaco.editor.getModel(uri);
-            monaco.editor.setModelMarkers(textModel, id, markers.map(reviveMarker));
+    $changeDiagnostics(id: string, delta: [string, MarkerData[]][]): void {
+        for (const [uriString, markers] of delta) {
+            const uri = new CoreURI(uriString);
+            this.problemManager.setMarkers(uri, id, markers.map(reviveMarker));
         }
     }
 
@@ -698,35 +693,56 @@ export class LanguagesMainImpl implements LanguagesMain {
     }
 }
 
-function reviveMarker(marker: MarkerData): monaco.editor.IMarkerData {
-    const monacoMarker: monaco.editor.IMarkerData = {
+function reviveMarker(marker: MarkerData): vst.Diagnostic {
+    const monacoMarker: vst.Diagnostic = {
         code: marker.code,
-        severity: marker.severity,
+        severity: reviveSeverity(marker.severity),
+        range: reviveRange(marker.startLineNumber, marker.startColumn, marker.endLineNumber, marker.endColumn),
         message: marker.message,
         source: marker.source,
-        startLineNumber: marker.startLineNumber,
-        startColumn: marker.startColumn,
-        endLineNumber: marker.endLineNumber,
-        endColumn: marker.endColumn,
         relatedInformation: undefined
     };
+
     if (marker.relatedInformation) {
-        monacoMarker.relatedInformation = [];
-        for (const ri of marker.relatedInformation) {
-            monacoMarker.relatedInformation.push({
-                resource: monaco.Uri.revive(ri.resource),
-                message: ri.message,
-                startLineNumber: ri.startLineNumber,
-                startColumn: ri.startColumn,
-                endLineNumber: ri.endLineNumber,
-                endColumn: ri.endColumn
-            });
-        }
+        monacoMarker.relatedInformation = marker.relatedInformation.map(reviveRelated);
     }
 
     return monacoMarker;
 }
 
+function reviveSeverity(severity: MarkerSeverity): vst.DiagnosticSeverity {
+    switch (severity) {
+        case MarkerSeverity.Error: return vst.DiagnosticSeverity.Error;
+        case MarkerSeverity.Warning: return vst.DiagnosticSeverity.Warning;
+        case MarkerSeverity.Info: return vst.DiagnosticSeverity.Information;
+        case MarkerSeverity.Hint: return vst.DiagnosticSeverity.Hint;
+    }
+}
+
+function reviveRange(startLine: number, startColumn: number, endLine: number, endColumn: number): vst.Range {
+    // note: language server range is 0-based, marker is 1-based, so need to deduct 1 here
+    return {
+        start: {
+            line: startLine - 1,
+            character: startColumn - 1
+        },
+        end: {
+            line: endLine - 1,
+            character: endColumn - 1
+        }
+    };
+}
+
+function reviveRelated(related: RelatedInformation): vst.DiagnosticRelatedInformation {
+    return {
+        message: related.message,
+        location: {
+            uri: related.resource,
+            range: reviveRange(related.startLineNumber, related.startColumn, related.endLineNumber, related.endColumn)
+        }
+    };
+}
+
 function reviveRegExp(regExp?: SerializedRegExp): RegExp | undefined {
     if (typeof regExp === 'undefined' || regExp === null) {
         return undefined;
diff --git a/packages/plugin-ext/src/plugin/languages/diagnostics.ts b/packages/plugin-ext/src/plugin/languages/diagnostics.ts
index 7951ce82f628d..3ef2bc0392f9b 100644
--- a/packages/plugin-ext/src/plugin/languages/diagnostics.ts
+++ b/packages/plugin-ext/src/plugin/languages/diagnostics.ts
@@ -114,7 +114,7 @@ export class DiagnosticCollection implements theia.DiagnosticCollection {
         if (this.has(uri)) {
             this.fireDiagnosticChangeEvent(uri);
             this.diagnostics.delete(uri.toString());
-            this.proxy.$changeDiagnostics(this.name, [[uri, []]]);
+            this.proxy.$changeDiagnostics(this.name, [[uri.toString(), []]]);
         }
     }
 
@@ -204,7 +204,7 @@ export class DiagnosticCollection implements theia.DiagnosticCollection {
     }
 
     private sendChangesToEditor(uris: URI[]): void {
-        const markers: [URI, MarkerData[]][] = [];
+        const markers: [string, MarkerData[]][] = [];
         nextUri:
         for (const uri of uris) {
             const uriMarkers: MarkerData[] = [];
@@ -224,7 +224,7 @@ export class DiagnosticCollection implements theia.DiagnosticCollection {
                                         endLineNumber: lastMarker.endLineNumber,
                                         endColumn: lastMarker.endColumn
                                     });
-                                    markers.push([uri, uriMarkers]);
+                                    markers.push([uri.toString(), uriMarkers]);
                                     continue nextUri;
                                 }
                             }
@@ -232,10 +232,10 @@ export class DiagnosticCollection implements theia.DiagnosticCollection {
                     }
                 } else {
                     uriDiagnostics.forEach(diagnostic => uriMarkers.push(convertDiagnosticToMarkerData(diagnostic)));
-                    markers.push([uri, uriMarkers]);
+                    markers.push([uri.toString(), uriMarkers]);
                 }
             } else {
-                markers.push([uri, []]);
+                markers.push([uri.toString(), []]);
             }
         }
 
diff --git a/packages/plugin-ext/src/plugin/type-converters.ts b/packages/plugin-ext/src/plugin/type-converters.ts
index e3309a24b1043..4c4709c4ea281 100644
--- a/packages/plugin-ext/src/plugin/type-converters.ts
+++ b/packages/plugin-ext/src/plugin/type-converters.ts
@@ -347,7 +347,7 @@ function convertRelatedInformation(diagnosticsRelatedInformation: theia.Diagnost
     const relatedInformation: model.RelatedInformation[] = [];
     for (const item of diagnosticsRelatedInformation) {
         relatedInformation.push({
-            resource: item.location.uri,
+            resource: item.location.uri.toString(),
             message: item.message,
             startLineNumber: item.location.range.start.line + 1,
             startColumn: item.location.range.start.character + 1,