diff --git a/src/vs/editor/common/modes.ts b/src/vs/editor/common/modes.ts
index da61c64e070..0616ed0e7a6 100644
--- a/src/vs/editor/common/modes.ts
+++ b/src/vs/editor/common/modes.ts
@@ -510,6 +510,11 @@ export interface CompletionContext {
  */
 export interface CompletionItemProvider {
 
+	/**
+	 * @internal
+	 */
+	_debugDisplayName?: string;
+
 	triggerCharacters?: string[];
 	/**
 	 * Provide completion items for the given position and document.
diff --git a/src/vs/editor/common/services/editorWorkerServiceImpl.ts b/src/vs/editor/common/services/editorWorkerServiceImpl.ts
index d42a7f7782e..6cefce59c2c 100644
--- a/src/vs/editor/common/services/editorWorkerServiceImpl.ts
+++ b/src/vs/editor/common/services/editorWorkerServiceImpl.ts
@@ -133,6 +133,8 @@ class WordBasedCompletionItemProvider implements modes.CompletionItemProvider {
 	private readonly _configurationService: ITextResourceConfigurationService;
 	private readonly _modelService: IModelService;
 
+	readonly _debugDisplayName = 'wordbasedCompletions';
+
 	constructor(
 		workerManager: WorkerManager,
 		configurationService: ITextResourceConfigurationService,
diff --git a/src/vs/editor/contrib/suggest/suggestWidget.ts b/src/vs/editor/contrib/suggest/suggestWidget.ts
index 7dabc8b16a5..fd6c81d0fac 100644
--- a/src/vs/editor/contrib/suggest/suggestWidget.ts
+++ b/src/vs/editor/contrib/suggest/suggestWidget.ts
@@ -37,6 +37,9 @@ import { IModelService } from 'vs/editor/common/services/modelService';
 import { URI } from 'vs/base/common/uri';
 import { IInstantiationService } from 'vs/platform/instantiation/common/instantiation';
 import { FileKind } from 'vs/platform/files/common/files';
+import { MarkdownString } from 'vs/base/common/htmlContent';
+import { KeybindingsRegistry, KeybindingWeight } from 'vs/platform/keybinding/common/keybindingsRegistry';
+import { KeyMod, KeyCode } from 'vs/base/common/keyCodes';
 
 const expandSuggestionDocsByDefault = false;
 
@@ -228,6 +231,18 @@ const enum State {
 	Details
 }
 
+
+let _explainMode = false;
+KeybindingsRegistry.registerCommandAndKeybindingRule({
+	id: 'suggest.toggleExplainMode',
+	handler() {
+		_explainMode = !_explainMode;
+	},
+	when: SuggestContext.Visible,
+	weight: KeybindingWeight.EditorContrib,
+	primary: KeyMod.CtrlCmd | KeyCode.US_SLASH,
+});
+
 class SuggestionDetails {
 
 	private el: HTMLElement;
@@ -247,7 +262,7 @@ class SuggestionDetails {
 		private readonly widget: SuggestWidget,
 		private readonly editor: ICodeEditor,
 		private readonly markdownRenderer: MarkdownRenderer,
-		private readonly triggerKeybindingLabel: string
+		private readonly triggerKeybindingLabel: string,
 	) {
 		this.disposables = [];
 
@@ -289,7 +304,19 @@ class SuggestionDetails {
 	renderItem(item: CompletionItem): void {
 		this.renderDisposeable = dispose(this.renderDisposeable);
 
-		if (!item || !canExpandCompletionItem(item)) {
+		let { documentation, detail } = item.completion;
+		// --- documentation
+
+		if (_explainMode) {
+			let md = '';
+			md += `score: ${item.score[0]}${item.word ? `, compared '${item.completion.filterText && (item.completion.filterText + ' (filterText)') || item.completion.label}' with '${item.word}'` : ' (no prefix)'}\n`;
+			md += `distance: ${item.distance}, see localityBonus-setting\n`;
+			md += `index: ${item.idx}, based on ${item.completion.sortText && `sortText: "${item.completion.sortText}"` || 'label'}\n`;
+			documentation = new MarkdownString().appendCodeblock('empty', md);
+			detail = `Provider: ${item.provider._debugDisplayName}`;
+		}
+
+		if (!_explainMode && !canExpandCompletionItem(item)) {
 			this.type.textContent = '';
 			this.docs.textContent = '';
 			addClass(this.el, 'no-docs');
@@ -297,19 +324,20 @@ class SuggestionDetails {
 			return;
 		}
 		removeClass(this.el, 'no-docs');
-		if (typeof item.completion.documentation === 'string') {
+		if (typeof documentation === 'string') {
 			removeClass(this.docs, 'markdown-docs');
-			this.docs.textContent = item.completion.documentation;
+			this.docs.textContent = documentation;
 		} else {
 			addClass(this.docs, 'markdown-docs');
 			this.docs.innerHTML = '';
-			const renderedContents = this.markdownRenderer.render(item.completion.documentation);
+			const renderedContents = this.markdownRenderer.render(documentation);
 			this.renderDisposeable = renderedContents;
 			this.docs.appendChild(renderedContents.element);
 		}
 
-		if (item.completion.detail) {
-			this.type.innerText = item.completion.detail;
+		// --- details
+		if (detail) {
+			this.type.innerText = detail;
 			show(this.type);
 		} else {
 			this.type.innerText = '';
@@ -333,8 +361,8 @@ class SuggestionDetails {
 
 		this.ariaLabel = strings.format(
 			'{0}{1}',
-			item.completion.detail || '',
-			item.completion.documentation ? (typeof item.completion.documentation === 'string' ? item.completion.documentation : item.completion.documentation.value) : '');
+			detail || '',
+			documentation ? (typeof documentation === 'string' ? documentation : documentation.value) : '');
 	}
 
 	getAriaLabel() {
@@ -479,7 +507,7 @@ export class SuggestWidget implements IContentWidget, IListVirtualDelegate<Compl
 
 		this.messageElement = append(this.element, $('.message'));
 		this.listElement = append(this.element, $('.tree'));
-		this.details = new SuggestionDetails(this.element, this, this.editor, markdownRenderer, triggerKeybindingLabel);
+		this.details = instantiationService.createInstance(SuggestionDetails, this.element, this, this.editor, markdownRenderer, triggerKeybindingLabel);
 
 		const applyIconStyle = () => toggleClass(this.element, 'no-icons', !this.editor.getConfiguration().contribInfo.suggest.showIcons);
 		applyIconStyle();
diff --git a/src/vs/workbench/api/browser/mainThreadLanguageFeatures.ts b/src/vs/workbench/api/browser/mainThreadLanguageFeatures.ts
index 1b55da3d731..d54e01d9a9b 100644
--- a/src/vs/workbench/api/browser/mainThreadLanguageFeatures.ts
+++ b/src/vs/workbench/api/browser/mainThreadLanguageFeatures.ts
@@ -346,9 +346,10 @@ export class MainThreadLanguageFeatures implements MainThreadLanguageFeaturesSha
 		};
 	}
 
-	$registerSuggestSupport(handle: number, selector: ISerializedDocumentFilter[], triggerCharacters: string[], supportsResolveDetails: boolean): void {
+	$registerSuggestSupport(handle: number, selector: ISerializedDocumentFilter[], triggerCharacters: string[], supportsResolveDetails: boolean, extensionId: ExtensionIdentifier): void {
 		const provider: modes.CompletionItemProvider = {
 			triggerCharacters,
+			_debugDisplayName: extensionId.value,
 			provideCompletionItems: (model: ITextModel, position: EditorPosition, context: modes.CompletionContext, token: CancellationToken): Promise<modes.CompletionList | undefined> => {
 				return this._proxy.$provideCompletionItems(handle, model.uri, position, context, token).then(result => {
 					if (!result) {
diff --git a/src/vs/workbench/api/common/extHost.protocol.ts b/src/vs/workbench/api/common/extHost.protocol.ts
index 2f51c54ee7c..f9f60f7dde7 100644
--- a/src/vs/workbench/api/common/extHost.protocol.ts
+++ b/src/vs/workbench/api/common/extHost.protocol.ts
@@ -348,7 +348,7 @@ export interface MainThreadLanguageFeaturesShape extends IDisposable {
 	$registerOnTypeFormattingSupport(handle: number, selector: ISerializedDocumentFilter[], autoFormatTriggerCharacters: string[], extensionId: ExtensionIdentifier): void;
 	$registerNavigateTypeSupport(handle: number): void;
 	$registerRenameSupport(handle: number, selector: ISerializedDocumentFilter[], supportsResolveInitialValues: boolean): void;
-	$registerSuggestSupport(handle: number, selector: ISerializedDocumentFilter[], triggerCharacters: string[], supportsResolveDetails: boolean): void;
+	$registerSuggestSupport(handle: number, selector: ISerializedDocumentFilter[], triggerCharacters: string[], supportsResolveDetails: boolean, extensionId: ExtensionIdentifier): void;
 	$registerSignatureHelpProvider(handle: number, selector: ISerializedDocumentFilter[], metadata: ISerializedSignatureHelpProviderMetadata): void;
 	$registerDocumentLinkProvider(handle: number, selector: ISerializedDocumentFilter[], supportsResolve: boolean): void;
 	$registerDocumentColorProvider(handle: number, selector: ISerializedDocumentFilter[]): void;
diff --git a/src/vs/workbench/api/common/extHostLanguageFeatures.ts b/src/vs/workbench/api/common/extHostLanguageFeatures.ts
index 4aefb1cc5d6..84e28939bb3 100644
--- a/src/vs/workbench/api/common/extHostLanguageFeatures.ts
+++ b/src/vs/workbench/api/common/extHostLanguageFeatures.ts
@@ -1380,7 +1380,7 @@ export class ExtHostLanguageFeatures implements ExtHostLanguageFeaturesShape {
 
 	registerCompletionItemProvider(extension: IExtensionDescription, selector: vscode.DocumentSelector, provider: vscode.CompletionItemProvider, triggerCharacters: string[]): vscode.Disposable {
 		const handle = this._addNewAdapter(new SuggestAdapter(this._documents, this._commands.converter, provider), extension);
-		this._proxy.$registerSuggestSupport(handle, this._transformDocumentSelector(selector), triggerCharacters, SuggestAdapter.supportsResolving(provider));
+		this._proxy.$registerSuggestSupport(handle, this._transformDocumentSelector(selector), triggerCharacters, SuggestAdapter.supportsResolving(provider), extension.identifier);
 		return this._createDisposable(handle);
 	}
 
diff --git a/src/vs/workbench/contrib/snippets/browser/snippetCompletionProvider.ts b/src/vs/workbench/contrib/snippets/browser/snippetCompletionProvider.ts
index 106ca8be945..87ca39e297c 100644
--- a/src/vs/workbench/contrib/snippets/browser/snippetCompletionProvider.ts
+++ b/src/vs/workbench/contrib/snippets/browser/snippetCompletionProvider.ts
@@ -64,6 +64,8 @@ export class SnippetCompletionProvider implements CompletionItemProvider {
 
 	private static readonly _maxPrefix = 10000;
 
+	readonly _debugDisplayName = 'snippetCompletions';
+
 	constructor(
 		@IModeService
 		private readonly _modeService: IModeService,