diff --git a/packages/language-server/src/plugins/typescript/LSAndTSDocResolver.ts b/packages/language-server/src/plugins/typescript/LSAndTSDocResolver.ts
index c90f21ae5..80ae3b864 100644
--- a/packages/language-server/src/plugins/typescript/LSAndTSDocResolver.ts
+++ b/packages/language-server/src/plugins/typescript/LSAndTSDocResolver.ts
@@ -19,6 +19,7 @@ export class LSAndTSDocResolver {
      * @param docManager
      * @param workspaceUris
      * @param configManager
+     * @param notifyExceedSizeLimit
      * @param isSvelteCheck True, if used in the context of svelte-check
      * @param tsconfigPath This should only be set via svelte-check. Makes sure all documents are resolved to that tsconfig. Has to be absolute.
      */
@@ -26,6 +27,7 @@ export class LSAndTSDocResolver {
         private readonly docManager: DocumentManager,
         private readonly workspaceUris: string[],
         private readonly configManager: LSConfigManager,
+        private readonly notifyExceedSizeLimit?: () => void,
         private readonly isSvelteCheck = false,
         private readonly tsconfigPath?: string
     ) {
@@ -69,7 +71,8 @@ export class LSAndTSDocResolver {
             ambientTypesSource: this.isSvelteCheck ? 'svelte-check' : 'svelte2tsx',
             createDocument: this.createDocument,
             transformOnTemplateError: !this.isSvelteCheck,
-            globalSnapshotsManager: this.globalSnapshotsManager
+            globalSnapshotsManager: this.globalSnapshotsManager,
+            notifyExceedSizeLimit: this.notifyExceedSizeLimit
         };
     }
 
diff --git a/packages/language-server/src/plugins/typescript/service.ts b/packages/language-server/src/plugins/typescript/service.ts
index bc1222782..dfa2f0ea7 100644
--- a/packages/language-server/src/plugins/typescript/service.ts
+++ b/packages/language-server/src/plugins/typescript/service.ts
@@ -13,7 +13,7 @@ import {
     ignoredBuildDirectories,
     SnapshotManager
 } from './SnapshotManager';
-import { ensureRealSvelteFilePath, findTsConfigPath } from './utils';
+import { ensureRealSvelteFilePath, findTsConfigPath, hasTsExtensions } from './utils';
 
 export interface LanguageServiceContainer {
     readonly tsconfigPath: string;
@@ -39,13 +39,16 @@ export interface LanguageServiceContainer {
     fileBelongsToProject(filePath: string): boolean;
 }
 
+const maxProgramSizeForNonTsFiles = 20 * 1024 * 1024; // 20 MB
 const services = new Map<string, Promise<LanguageServiceContainer>>();
+const serviceSizeMap: Map<string, number> = new Map();
 
 export interface LanguageServiceDocumentContext {
     ambientTypesSource: string;
     transformOnTemplateError: boolean;
     createDocument: (fileName: string, content: string) => Document;
     globalSnapshotsManager: GlobalSnapshotsManager;
+    notifyExceedSizeLimit: (() => void) | undefined;
 }
 
 export async function getService(
@@ -123,12 +126,14 @@ async function createLanguageService(
         './svelte-native-jsx.d.ts'
     ].map((f) => ts.sys.resolvePath(resolve(svelteTsPath, f)));
 
+    let languageServiceReducedMode = false;
+
     const host: ts.LanguageServiceHost = {
         getCompilationSettings: () => compilerOptions,
         getScriptFileNames: () =>
             Array.from(
                 new Set([
-                    ...snapshotManager.getProjectFileNames(),
+                    ...(languageServiceReducedMode ? [] : snapshotManager.getProjectFileNames()),
                     ...snapshotManager.getFileNames(),
                     ...svelteTsxFiles
                 ])
@@ -150,6 +155,8 @@ async function createLanguageService(
         transformOnTemplateError: docContext.transformOnTemplateError
     };
 
+    reduceLanguageServiceCapabilityIfFileSizeTooBig();
+
     return {
         tsconfigPath,
         compilerOptions,
@@ -232,7 +239,15 @@ async function createLanguageService(
     }
 
     function updateProjectFiles(): void {
+        const projectFileCountBefore = snapshotManager.getProjectFileNames().length;
         snapshotManager.updateProjectFiles();
+        const projectFileCountAfter = snapshotManager.getProjectFileNames().length;
+
+        if (projectFileCountAfter <= projectFileCountBefore) {
+            return;
+        }
+
+        reduceLanguageServiceCapabilityIfFileSizeTooBig();
     }
 
     function hasFile(filePath: string): boolean {
@@ -350,4 +365,68 @@ async function createLanguageService(
     function getDefaultExclude() {
         return ['node_modules', ...ignoredBuildDirectories];
     }
+
+    /**
+     * Disable usage of project files.
+     * running language service in a reduced mode for
+     * large projects with improperly excluded tsconfig.
+     */
+    function reduceLanguageServiceCapabilityIfFileSizeTooBig() {
+        if (exceedsTotalSizeLimitForNonTsFiles(compilerOptions, tsconfigPath, snapshotManager)) {
+            languageService.cleanupSemanticCache();
+            languageServiceReducedMode = true;
+            docContext.notifyExceedSizeLimit?.();
+        }
+    }
+}
+
+/**
+ * adopted from https://github.com/microsoft/TypeScript/blob/3c8e45b304b8572094c5d7fbb9cd768dbf6417c0/src/server/editorServices.ts#L1955
+ */
+function exceedsTotalSizeLimitForNonTsFiles(
+    compilerOptions: ts.CompilerOptions,
+    tsconfigPath: string,
+    snapshotManager: SnapshotManager
+): boolean {
+    if (compilerOptions.disableSizeLimit) {
+        return false;
+    }
+
+    let availableSpace = maxProgramSizeForNonTsFiles;
+    serviceSizeMap.set(tsconfigPath, 0);
+
+    serviceSizeMap.forEach((size) => {
+        availableSpace -= size;
+    });
+
+    let totalNonTsFileSize = 0;
+
+    const fileNames = snapshotManager.getProjectFileNames();
+    for (const fileName of fileNames) {
+        if (hasTsExtensions(fileName)) {
+            continue;
+        }
+
+        totalNonTsFileSize += ts.sys.getFileSize?.(fileName) ?? 0;
+
+        if (totalNonTsFileSize > availableSpace) {
+            const top5LargestFiles = fileNames
+                .filter((name) => !hasTsExtensions(name))
+                .map((name) => ({ name, size: ts.sys.getFileSize?.(name) ?? 0 }))
+                .sort((a, b) => b.size - a.size)
+                .slice(0, 5);
+
+            Logger.log(
+                `Non TS file size exceeded limit (${totalNonTsFileSize}). ` +
+                    `Largest files: ${top5LargestFiles
+                        .map((file) => `${file.name}:${file.size}`)
+                        .join(', ')}`
+            );
+
+            return true;
+        }
+    }
+
+    serviceSizeMap.set(tsconfigPath, totalNonTsFileSize);
+    return false;
 }
diff --git a/packages/language-server/src/plugins/typescript/utils.ts b/packages/language-server/src/plugins/typescript/utils.ts
index c6c120ef3..7a24fa9e8 100644
--- a/packages/language-server/src/plugins/typescript/utils.ts
+++ b/packages/language-server/src/plugins/typescript/utils.ts
@@ -313,3 +313,11 @@ export function getDiagnosticTag(diagnostic: ts.Diagnostic): DiagnosticTag[] {
     }
     return tags;
 }
+
+export function hasTsExtensions(fileName: string) {
+    return (
+        fileName.endsWith(ts.Extension.Dts) ||
+        fileName.endsWith(ts.Extension.Tsx) ||
+        fileName.endsWith(ts.Extension.Ts)
+    );
+}
diff --git a/packages/language-server/src/server.ts b/packages/language-server/src/server.ts
index 140d38e8c..b6aa6467d 100644
--- a/packages/language-server/src/server.ts
+++ b/packages/language-server/src/server.ts
@@ -145,7 +145,12 @@ export function startServer(options?: LSOptions) {
         pluginHost.register(
             new TypeScriptPlugin(
                 configManager,
-                new LSAndTSDocResolver(docManager, workspaceUris.map(normalizeUri), configManager)
+                new LSAndTSDocResolver(
+                    docManager,
+                    workspaceUris.map(normalizeUri),
+                    configManager,
+                    notifyTsServiceExceedSizeLimit
+                )
             )
         );
 
@@ -241,6 +246,16 @@ export function startServer(options?: LSOptions) {
         };
     });
 
+    function notifyTsServiceExceedSizeLimit() {
+        connection?.sendNotification(ShowMessageNotification.type, {
+            message:
+                'Svelte language server detected a large amount of JS/Svelte files. ' +
+                'To enable project-wide JavaScript/TypeScript language features for Svelte files,' +
+                'exclude large folders in the tsconfig.json or jsconfig.json with source files that you do not work on.',
+            type: MessageType.Warning
+        });
+    }
+
     connection.onExit(() => {
         watcher?.dispose();
     });
diff --git a/packages/language-server/src/svelte-check.ts b/packages/language-server/src/svelte-check.ts
index 042418eb0..0671ed728 100644
--- a/packages/language-server/src/svelte-check.ts
+++ b/packages/language-server/src/svelte-check.ts
@@ -64,6 +64,7 @@ export class SvelteCheck {
                 this.docManager,
                 [pathToUrl(workspacePath)],
                 this.configManager,
+                undefined,
                 true,
                 options.tsconfig
             );