diff --git a/packages/flutter_tools/lib/src/build_system/targets/web.dart b/packages/flutter_tools/lib/src/build_system/targets/web.dart
index b90d21a5200..3f0bed672cd 100644
--- a/packages/flutter_tools/lib/src/build_system/targets/web.dart
+++ b/packages/flutter_tools/lib/src/build_system/targets/web.dart
@@ -745,6 +745,7 @@ _flutter.buildConfig = ${jsonEncode(buildConfig)};
       serviceWorkerVersion: serviceWorkerVersion,
       flutterJsFile: flutterJsFile,
       buildConfig: buildConfig,
+      logger: environment.logger,
       webDefines: webDefines,
     );
 
@@ -769,6 +770,7 @@ _flutter.buildConfig = ${jsonEncode(buildConfig)};
           flutterJsFile: flutterJsFile,
           buildConfig: buildConfig,
           flutterBootstrapJs: bootstrapContent,
+          logger: environment.logger,
           webDefines: webDefines,
         );
         final File outputIndexHtml = fileSystem.file(
diff --git a/packages/flutter_tools/lib/src/isolated/web_asset_server.dart b/packages/flutter_tools/lib/src/isolated/web_asset_server.dart
index 6f987c1ba41..639501bc23c 100644
--- a/packages/flutter_tools/lib/src/isolated/web_asset_server.dart
+++ b/packages/flutter_tools/lib/src/isolated/web_asset_server.dart
@@ -79,6 +79,7 @@ class WebAssetServer implements AssetReader {
     required this.webRenderer,
     required this.useLocalCanvasKit,
     required this.fileSystem,
+    required this.logger,
     Map<String, String> webDefines = const <String, String>{},
   }) : basePath = WebTemplate.baseHref(htmlTemplate(fileSystem, 'index.html', _kDefaultIndex)),
        _webDefines = webDefines {
@@ -266,6 +267,7 @@ class WebAssetServer implements AssetReader {
       webRenderer: webRenderer,
       useLocalCanvasKit: useLocalCanvasKit,
       fileSystem: fileSystem,
+      logger: logger,
       webDefines: webDefines,
     );
     final int selectedPort = server.selectedPort;
@@ -595,6 +597,7 @@ class WebAssetServer implements AssetReader {
   final bool useLocalCanvasKit;
 
   final FileSystem fileSystem;
+  final Logger logger;
 
   String get _buildConfigString {
     final buildConfig = <String, Object>{
@@ -634,6 +637,7 @@ _flutter.buildConfig = ${jsonEncode(buildConfig)};
       serviceWorkerVersion: null,
       buildConfig: _buildConfigString,
       flutterJsFile: _flutterJsFile,
+      logger: logger,
       webDefines: _webDefines,
     );
   }
@@ -657,6 +661,7 @@ _flutter.buildConfig = ${jsonEncode(buildConfig)};
         buildConfig: _buildConfigString,
         flutterJsFile: _flutterJsFile,
         flutterBootstrapJs: _flutterBootstrapJsContent,
+        logger: logger,
         webDefines: _webDefines,
       ),
       encoding: utf8,
diff --git a/packages/flutter_tools/lib/src/runner/flutter_command.dart b/packages/flutter_tools/lib/src/runner/flutter_command.dart
index 091be82f457..74c50ead025 100644
--- a/packages/flutter_tools/lib/src/runner/flutter_command.dart
+++ b/packages/flutter_tools/lib/src/runner/flutter_command.dart
@@ -774,7 +774,7 @@ abstract class FlutterCommand extends Command<void> {
           'Variables are replaced in the format {{VARIABLE_NAME}}.\n'
           'Multiple defines can be passed by repeating "--${FlutterOptions.kWebDefinesOption}" multiple times.\n'
           'If a template contains a variable placeholder but no corresponding "--web-define" is provided, '
-          'the build will fail with an error.',
+          'it will warn that you have an unhandled variable.',
       valueHelp: 'API_URL=https://api.example.com',
       splitCommas: false,
     );
diff --git a/packages/flutter_tools/lib/src/web_template.dart b/packages/flutter_tools/lib/src/web_template.dart
index 919f3eefc19..2910236167a 100644
--- a/packages/flutter_tools/lib/src/web_template.dart
+++ b/packages/flutter_tools/lib/src/web_template.dart
@@ -8,6 +8,7 @@ import 'package:meta/meta.dart';
 
 import 'base/common.dart';
 import 'base/file_system.dart';
+import 'base/logger.dart';
 import 'base/utils.dart';
 
 /// Placeholder for base href
@@ -107,6 +108,7 @@ class WebTemplate {
     String? buildConfig,
     String? flutterBootstrapJs,
     String? staticAssetsUrl,
+    required Logger logger,
     Map<String, String> webDefines = const <String, String>{},
   }) {
     String newContent = _content;
@@ -133,7 +135,7 @@ class WebTemplate {
             "navigator.serviceWorker.register('flutter_service_worker.js?v=$serviceWorkerVersion') /* $_kServiceWorkerDeprecationNotice */",
           );
     }
-    newContent = _applyVariableSubstitutions(newContent, <String, String>{
+    newContent = _applyVariableSubstitutions(newContent, logger, <String, String>{
       ...webDefines,
       if (buildConfig != null) 'flutter_build_config': buildConfig,
       if (flutterBootstrapJs != null) 'flutter_bootstrap_js': flutterBootstrapJs,
@@ -149,8 +151,13 @@ class WebTemplate {
   /// Applies web-define variable substitutions and validates all variables are provided.
   ///
   /// Replaces {{VARIABLE}} placeholders with values from webDefines. Built-in Flutter
-  /// variables are preserved if missing; user-defined variables throw ToolExit.
-  String _applyVariableSubstitutions(String content, Map<String, String> webDefines) {
+  /// variables are preserved if missing; user-defined variables will log a warning
+  /// and be skipped.
+  String _applyVariableSubstitutions(
+    String content,
+    Logger logger,
+    Map<String, String> webDefines,
+  ) {
     final variablePattern = RegExp(r'\{\{([A-Za-z_][A-Za-z0-9_]*)\}\}');
     final missingVariables = <String>{};
 
@@ -188,13 +195,16 @@ class WebTemplate {
         .map((String name) => '--web-define=$name=VALUE')
         .join(' ');
     final String variablesList = pluralize('variable', missingVariables.length);
-    throwToolExit(
-      'Missing web-define $variablesList: $variables\n\n'
-      'Please provide the missing $variablesList using:\n'
+    logger.printWarning(
+      'Warning: Missing web-define $variablesList: $variables\n\n'
+      'You can provide the missing $variablesList using:\n'
       'flutter run $suggestion\n'
       'or\n'
-      'flutter build web $suggestion',
+      'flutter build web $suggestion\n'
+      'This variable will be skipped.\n',
     );
+
+    return result;
   }
 }
 
diff --git a/packages/flutter_tools/test/general.shard/web/devfs_web_ddc_modules_test.dart b/packages/flutter_tools/test/general.shard/web/devfs_web_ddc_modules_test.dart
index 3a0a1184d21..682792b4f2a 100644
--- a/packages/flutter_tools/test/general.shard/web/devfs_web_ddc_modules_test.dart
+++ b/packages/flutter_tools/test/general.shard/web/devfs_web_ddc_modules_test.dart
@@ -81,6 +81,7 @@ void main() {
           webRenderer: WebRendererMode.canvaskit,
           useLocalCanvasKit: false,
           fileSystem: globals.fs,
+          logger: logger,
         );
         releaseAssetServer = ReleaseAssetServer(
           globals.fs.file('main.dart').uri,
@@ -329,6 +330,7 @@ void main() {
       webRenderer: WebRendererMode.canvaskit,
       useLocalCanvasKit: false,
       fileSystem: globals.fs,
+      logger: logger,
     );
 
     expect(webAssetServer.basePath, 'foo/bar');
@@ -350,6 +352,7 @@ void main() {
       webRenderer: WebRendererMode.canvaskit,
       useLocalCanvasKit: false,
       fileSystem: globals.fs,
+      logger: logger,
     );
 
     // Defaults to "/" when there's no base element.
@@ -373,6 +376,7 @@ void main() {
         webRenderer: WebRendererMode.canvaskit,
         useLocalCanvasKit: false,
         fileSystem: globals.fs,
+        logger: logger,
       ),
       throwsToolExit(),
     );
@@ -395,6 +399,7 @@ void main() {
         webRenderer: WebRendererMode.canvaskit,
         useLocalCanvasKit: false,
         fileSystem: globals.fs,
+        logger: logger,
       ),
       throwsToolExit(),
     );
@@ -1216,6 +1221,7 @@ void main() {
       webRenderer: WebRendererMode.canvaskit,
       useLocalCanvasKit: false,
       fileSystem: globals.fs,
+      logger: logger,
     );
 
     expect(await webAssetServer.metadataContents('foo/main_module.ddc_merged_metadata'), null);
diff --git a/packages/flutter_tools/test/general.shard/web/devfs_web_test.dart b/packages/flutter_tools/test/general.shard/web/devfs_web_test.dart
index 61996302213..195e5c29ef4 100644
--- a/packages/flutter_tools/test/general.shard/web/devfs_web_test.dart
+++ b/packages/flutter_tools/test/general.shard/web/devfs_web_test.dart
@@ -80,6 +80,7 @@ void main() {
           webRenderer: WebRendererMode.canvaskit,
           useLocalCanvasKit: false,
           fileSystem: globals.fs,
+          logger: logger,
         );
         releaseAssetServer = ReleaseAssetServer(
           globals.fs.file('main.dart').uri,
@@ -352,6 +353,7 @@ void main() {
         webRenderer: WebRendererMode.canvaskit,
         useLocalCanvasKit: false,
         fileSystem: globals.fs,
+        logger: logger,
       );
 
       expect(webAssetServer.basePath, 'foo/bar');
@@ -376,6 +378,7 @@ void main() {
         webRenderer: WebRendererMode.canvaskit,
         useLocalCanvasKit: false,
         fileSystem: globals.fs,
+        logger: logger,
       );
 
       // Defaults to "/" when there's no base element.
@@ -402,6 +405,7 @@ void main() {
           webRenderer: WebRendererMode.canvaskit,
           useLocalCanvasKit: false,
           fileSystem: globals.fs,
+          logger: logger,
         ),
         throwsToolExit(),
       );
@@ -427,6 +431,7 @@ void main() {
           webRenderer: WebRendererMode.canvaskit,
           useLocalCanvasKit: false,
           fileSystem: globals.fs,
+          logger: logger,
         ),
         throwsToolExit(),
       );
@@ -500,6 +505,7 @@ void main() {
         webRenderer: WebRendererMode.canvaskit,
         useLocalCanvasKit: true,
         fileSystem: globals.fs,
+        logger: logger,
       );
 
       final Response response = await webAssetServer.handleRequest(
@@ -1530,6 +1536,7 @@ void main() {
         webRenderer: WebRendererMode.canvaskit,
         useLocalCanvasKit: false,
         fileSystem: globals.fs,
+        logger: logger,
       );
 
       expect(await webAssetServer.metadataContents('foo/main_module.ddc_merged_metadata'), null);
@@ -1596,7 +1603,7 @@ void main() {
   );
 
   test(
-    'WebAssetServer serves index.html with web-define variables',
+    'WebAssetServer serves index.html without user defined web-define variables',
     () => testbed.run(() async {
       // Simple test case with no custom variables - should work like before
       globals.fs.file(
@@ -1619,6 +1626,7 @@ void main() {
         webRenderer: WebRendererMode.canvaskit,
         useLocalCanvasKit: false,
         fileSystem: globals.fs,
+        logger: logger,
       );
 
       final Response response = await webAssetServer.handleRequest(
@@ -1629,7 +1637,7 @@ void main() {
   );
 
   test(
-    'WebAssetServer throws error for missing web-define variables in index.html',
+    'WebAssetServer warns for missing user defined web-define variables in index.html',
     () => testbed.run(() async {
       const htmlContent = '''
 <!DOCTYPE html>
@@ -1670,11 +1678,78 @@ void main() {
         useLocalCanvasKit: false,
         fileSystem: globals.fs,
         webDefines: <String, String>{}, // Empty webDefines
+        logger: logger,
       );
 
+      final Response response = await webAssetServer.handleRequest(
+        Request('GET', Uri.parse('http://foobar/')),
+      );
+
+      expect(response.statusCode, HttpStatus.ok);
+      // Verify the placeholder is preserved
+      expect(await response.readAsString(), contains("const apiUrl = '{{MISSING_VAR}}';"));
+      expect(logger.warningText, contains('Missing web-define variable: MISSING_VAR'));
+    }),
+  );
+
+  test(
+    'WebAssetServer logs warning for multiple missing web-define variables in index.html',
+    () => testbed.run(() async {
+      const htmlContent = '''
+<!DOCTYPE html>
+<html>
+<head>
+  <title>Test</title>
+  <base href="/">
+</head>
+<body>
+  <script>
+    const apiUrl = '{{MISSING_VAR_1}}';
+    const apiKey = '{{MISSING_VAR_2}}';
+  </script>
+</body>
+</html>''';
+
+      globals.fs.currentDirectory.childDirectory('web').childFile('index.html')
+        ..createSync(recursive: true)
+        ..writeAsStringSync(htmlContent);
+
+      globals.fs.file(
+          globals.fs.path.join(
+            globals.artifacts!.getHostArtifact(HostArtifact.flutterJsDirectory).path,
+            'flutter.js',
+          ),
+        )
+        ..createSync(recursive: true)
+        ..writeAsStringSync('flutter.js content');
+
+      final webAssetServer = WebAssetServer(
+        FakeHttpServer(),
+        PackageConfig.empty,
+        InternetAddress.anyIPv4,
+        <String, String>{},
+        <String, String>{},
+        usesDdcModuleSystem,
+        canaryFeatures,
+        webRenderer: WebRendererMode.canvaskit,
+        useLocalCanvasKit: false,
+        fileSystem: globals.fs,
+        webDefines: <String, String>{}, // Empty webDefines
+        logger: logger,
+      );
+
+      final Response response = await webAssetServer.handleRequest(
+        Request('GET', Uri.parse('http://foobar/')),
+      );
+
+      expect(response.statusCode, HttpStatus.ok);
+      // Verify the placeholders are preserved
+      final String responseBody = await response.readAsString();
+      expect(responseBody, contains("const apiUrl = '{{MISSING_VAR_1}}';"));
+      expect(responseBody, contains("const apiKey = '{{MISSING_VAR_2}}';"));
       expect(
-        () async => webAssetServer.handleRequest(Request('GET', Uri.parse('http://foobar/'))),
-        throwsToolExit(message: 'Missing web-define variable: MISSING_VAR'),
+        logger.warningText,
+        contains('Missing web-define variables: MISSING_VAR_1, MISSING_VAR_2'),
       );
     }),
   );
@@ -1715,6 +1790,7 @@ const config = {
         useLocalCanvasKit: false,
         fileSystem: globals.fs,
         webDefines: <String, String>{'API_URL': 'https://test.api.com', 'DEBUG_MODE': 'true'},
+        logger: logger,
       );
 
       final Response response = await webAssetServer.handleRequest(
diff --git a/packages/flutter_tools/test/general.shard/web_template_test.dart b/packages/flutter_tools/test/general.shard/web_template_test.dart
index a2b03907321..63b61a34561 100644
--- a/packages/flutter_tools/test/general.shard/web_template_test.dart
+++ b/packages/flutter_tools/test/general.shard/web_template_test.dart
@@ -4,9 +4,12 @@
 
 import 'package:file/file.dart';
 import 'package:file/memory.dart';
+
+import 'package:flutter_tools/src/base/logger.dart';
 import 'package:flutter_tools/src/web_template.dart';
 
 import '../src/common.dart';
+import '../src/context.dart';
 
 const htmlSample1 = '''
 <!DOCTYPE html>
@@ -285,6 +288,7 @@ String htmlSampleStaticAssetsUrlReplaced({required String staticAssetsUrl}) =>
 
 void main() {
   final fs = MemoryFileSystem();
+  final logger = BufferLogger.test();
   final File flutterJs = fs.file('flutter.js');
   flutterJs.writeAsStringSync('(flutter.js content)');
 
@@ -316,6 +320,7 @@ void main() {
         baseHref: '/foo/333/',
         serviceWorkerVersion: 'v123xyz',
         flutterJsFile: flutterJs,
+        logger: logger,
       ),
       htmlSample2Replaced(baseHref: '/foo/333/', serviceWorkerVersion: 'v123xyz'),
     );
@@ -328,6 +333,7 @@ void main() {
         baseHref: '/foo/333/',
         serviceWorkerVersion: 'v123xyz',
         flutterJsFile: flutterJs,
+        logger: logger,
       ),
       htmlSample2Replaced(baseHref: '/foo/333/', serviceWorkerVersion: 'v123xyz'),
     );
@@ -343,6 +349,7 @@ void main() {
         serviceWorkerVersion: '(service worker version)',
         flutterJsFile: flutterJs,
         buildConfig: '(build config)',
+        logger: logger,
       ),
       htmlSampleInlineFlutterJsBootstrapOutput,
     );
@@ -359,6 +366,7 @@ void main() {
         flutterJsFile: flutterJs,
         buildConfig: '(build config)',
         flutterBootstrapJs: '(flutter bootstrap script)',
+        logger: logger,
       ),
       htmlSampleFullFlutterBootstrapReplacementOutput,
     );
@@ -374,6 +382,7 @@ void main() {
         serviceWorkerVersion: 'v123xyz',
         flutterJsFile: flutterJs,
         staticAssetsUrl: expectedStaticAssetsUrl,
+        logger: logger,
       ),
       htmlSampleStaticAssetsUrlReplaced(staticAssetsUrl: expectedStaticAssetsUrl),
     );
@@ -387,6 +396,7 @@ void main() {
       baseHref: '/foo/333/',
       serviceWorkerVersion: 'v123xyz',
       flutterJsFile: flutterJs,
+      logger: logger,
     );
     // The parsed base href should be updated after substitutions.
     expect(WebTemplate.baseHref(substituted), 'foo/333');
@@ -452,6 +462,7 @@ void main() {
         'ENV': 'production',
         'DEBUG_MODE': 'false',
       },
+      logger: logger,
     );
 
     expect(result, contains("apiUrl: 'https://api.example.com'"));
@@ -459,7 +470,7 @@ void main() {
     expect(result, contains('debugMode: false'));
   });
 
-  test('throws ToolExit when web-define variable is missing', () {
+  testUsingContext('logs warning when user defined web-define variable is missing', () {
     const htmlWithMissingVar = '''
 <!DOCTYPE html>
 <html>
@@ -475,18 +486,20 @@ void main() {
 </html>''';
 
     const indexHtml = WebTemplate(htmlWithMissingVar);
-    expect(
-      () => indexHtml.withSubstitutions(
-        baseHref: '/',
-        serviceWorkerVersion: null,
-        flutterJsFile: flutterJs,
-        webDefines: <String, String>{}, // Missing API_URL
-      ),
-      throwsToolExit(message: 'Missing web-define variable: API_URL'),
+    final String result = indexHtml.withSubstitutions(
+      baseHref: '/',
+      serviceWorkerVersion: null,
+      flutterJsFile: flutterJs,
+      webDefines: <String, String>{}, // Missing API_URL
+      logger: testLogger,
     );
+
+    expect(testLogger.warningText, contains('Missing web-define variable: API_URL'));
+    // Verify the placeholder is preserved
+    expect(result, contains("const apiUrl = '{{API_URL}}';"));
   });
 
-  test('throws ToolExit with multiple missing variables', () {
+  testUsingContext('logs warning with multiple missing user defined variables', () {
     const htmlWithMultipleMissingVars = '''
 <!DOCTYPE html>
 <html>
@@ -506,19 +519,23 @@ void main() {
 </html>''';
 
     const indexHtml = WebTemplate(htmlWithMultipleMissingVars);
-    expect(
-      () => indexHtml.withSubstitutions(
-        baseHref: '/',
-        serviceWorkerVersion: null,
-        flutterJsFile: flutterJs,
-        webDefines: <String, String>{'API_URL': 'test'}, // Missing ENV, VERSION
-      ),
-      throwsToolExit(message: 'Missing web-define variable'),
+    final String result = indexHtml.withSubstitutions(
+      baseHref: '/',
+      serviceWorkerVersion: null,
+      flutterJsFile: flutterJs,
+      webDefines: <String, String>{'API_URL': 'test'}, // Missing ENV, VERSION
+      logger: testLogger,
     );
+
+    expect(testLogger.warningText, contains('Missing web-define variables: ENV, VERSION'));
+    expect(result, contains("env: '{{ENV}}'"));
+    expect(result, contains("version: '{{VERSION}}'"));
   });
 
-  test('ignores Flutter built-in variables when validating web-define variables', () {
-    const htmlWithBuiltInVars = '''
+  testUsingContext(
+    'ignores Flutter built-in variables and logs warning for missing user variables',
+    () {
+      const htmlWithBuiltInVars = '''
 <!DOCTYPE html>
 <html>
 <head>
@@ -534,18 +551,20 @@ void main() {
 </body>
 </html>''';
 
-    const indexHtml = WebTemplate(htmlWithBuiltInVars);
-    expect(
-      () => indexHtml.withSubstitutions(
+      const indexHtml = WebTemplate(htmlWithBuiltInVars);
+      final String result = indexHtml.withSubstitutions(
         baseHref: '/',
         serviceWorkerVersion: null,
         flutterJsFile: flutterJs,
         buildConfig: 'test config',
         webDefines: <String, String>{}, // Missing CUSTOM_VAR but built-in vars should be ignored
-      ),
-      throwsToolExit(message: 'Missing web-define variable: CUSTOM_VAR'),
-    );
-  });
+        logger: testLogger,
+      );
+
+      expect(testLogger.warningText, contains('Missing web-define variable: CUSTOM_VAR'));
+      expect(result, contains("const customVar = '{{CUSTOM_VAR}}';"));
+    },
+  );
 
   test('allows empty web-define variables', () {
     const htmlWithEmptyVar = '''
@@ -568,6 +587,7 @@ void main() {
       serviceWorkerVersion: null,
       flutterJsFile: flutterJs,
       webDefines: <String, String>{'EMPTY_VAR': ''},
+      logger: logger,
     );
 
     expect(result, contains("const value = '';"));