diff --git a/pkgs/test/CHANGELOG.md b/pkgs/test/CHANGELOG.md
index 04ef333c1..68519d4d3 100644
--- a/pkgs/test/CHANGELOG.md
+++ b/pkgs/test/CHANGELOG.md
@@ -4,6 +4,7 @@
 * Increase SDK constraint to ^3.5.0-311.0.dev.
 * Support running Node.js tests compiled with dart2wasm.
 * Allow `firefox` or `firefox-bin` executable name on macOS.
+* Use a DevTools URL instead of a defunct observatory URL.
 
 ## 1.25.8
 
diff --git a/pkgs/test_core/CHANGELOG.md b/pkgs/test_core/CHANGELOG.md
index 610311022..34af12c9d 100644
--- a/pkgs/test_core/CHANGELOG.md
+++ b/pkgs/test_core/CHANGELOG.md
@@ -3,6 +3,7 @@
 * Fix dart2wasm tests on windows.
 * Increase SDK constraint to ^3.5.0-311.0.dev.
 * Allow passing additional arguments to `dart compile wasm`.
+* Use a DevTools URL instead of a defunct observatory URL.
 
 ## 0.6.5
 
diff --git a/pkgs/test_core/lib/src/runner/environment.dart b/pkgs/test_core/lib/src/runner/environment.dart
index 7fcba66eb..67e64de1f 100644
--- a/pkgs/test_core/lib/src/runner/environment.dart
+++ b/pkgs/test_core/lib/src/runner/environment.dart
@@ -12,8 +12,9 @@ abstract class Environment {
   /// Whether this environment supports interactive debugging.
   bool get supportsDebugging;
 
-  /// The URL of the Dart VM Observatory for this environment, or `null` if this
-  /// environment doesn't run the Dart VM or the URL couldn't be detected.
+  /// The URL of the Dart Dev Tools server for this environment, or `null` if
+  /// this environment doesn't run the Dart VM or the URL couldn't be detected.
+  // TODO(https://github.com/dart-lang/test/issues/2185) rename to `devToolsUrl`
   Uri? get observatoryUrl;
 
   /// The URL of the remote debugger for this environment, or `null` if it isn't
diff --git a/pkgs/test_core/lib/src/runner/vm/platform.dart b/pkgs/test_core/lib/src/runner/vm/platform.dart
index 506909db7..23e2565a6 100644
--- a/pkgs/test_core/lib/src/runner/vm/platform.dart
+++ b/pkgs/test_core/lib/src/runner/vm/platform.dart
@@ -107,6 +107,8 @@ class VMPlatform extends PlatformPlugin {
 
     Environment? environment;
     IsolateRef? isolateRef;
+    String? isolateID;
+    Uri? serverUri;
     if (_config.debug) {
       if (platform.compiler == Compiler.exe) {
         throw UnsupportedError(
@@ -115,21 +117,17 @@ class VMPlatform extends PlatformPlugin {
       }
       var info =
           await Service.controlWebServer(enable: true, silenceOutput: true);
-      // ignore: deprecated_member_use, Remove when SDK constraint is at 3.2.0
-      var isolateID = Service.getIsolateID(isolate!)!;
+      serverUri = info.serverUri!;
+      isolateID = Service.getIsolateId(isolate!)!;
 
-      var libraryPath = (await absoluteUri(path)).toString();
-      var serverUri = info.serverUri!;
-      client = await vmServiceConnectUri(_wsUriFor(serverUri).toString());
+      var serviceWebsocket = _wsUriFor(serverUri);
+      client = await vmServiceConnectUri(serviceWebsocket.toString());
       var isolateNumber = int.parse(isolateID.split('/').last);
       isolateRef = (await client.getVM())
           .isolates!
           .firstWhere((isolate) => isolate.number == isolateNumber.toString());
       await client.setName(isolateRef.id!, path);
-      var libraryRef = (await client.getIsolate(isolateRef.id!))
-          .libraries!
-          .firstWhere((library) => library.uri == libraryPath);
-      var url = _observatoryUrlFor(serverUri, isolateRef.id!, libraryRef.id!);
+      var url = _devtoolsUriFor(serviceWebsocket);
       environment = VMEnvironment(url, isolateRef, client);
     }
 
@@ -137,7 +135,7 @@ class VMPlatform extends PlatformPlugin {
 
     var controller = deserializeSuite(
         path, platform, suiteConfig, environment, channel.cast(), message,
-        gatherCoverage: () => _gatherCoverage(environment!));
+        gatherCoverage: () => _gatherCoverage(serverUri!, isolateID!));
 
     if (isolateRef != null) {
       await client!.streamListen('Debug');
@@ -331,20 +329,23 @@ stderr: ${processResult.stderr}''');
   }
 }
 
-Future<Map<String, dynamic>> _gatherCoverage(Environment environment) async {
-  final isolateId = Uri.parse(environment.observatoryUrl!.fragment)
-      .queryParameters['isolateId'];
-  return await collect(environment.observatoryUrl!, false, false, false, {},
-      isolateIds: {isolateId!});
+Future<Map<String, dynamic>> _gatherCoverage(
+    Uri serviceUri, String isolateId) async {
+  return await collect(serviceUri, false, false, false, {},
+      isolateIds: {isolateId});
 }
 
 Uri _wsUriFor(Uri observatoryUrl) =>
     observatoryUrl.replace(scheme: 'ws').resolve('ws');
 
-Uri _observatoryUrlFor(Uri base, String isolateId, String id) => base.replace(
-    fragment: Uri(
-        path: '/inspect',
-        queryParameters: {'isolateId': isolateId, 'objectId': id}).toString());
+Uri _devtoolsUriFor(Uri serviceUri) {
+  assert(serviceUri.isScheme('ws'));
+  return serviceUri.resolve('devtools/debugger').replace(
+        scheme: 'http',
+        queryParameters: {'uri': '$serviceUri'},
+        fragment: '',
+      );
+}
 
 var _hasRegistered = false;
 void _setupPauseAfterTests() {