flutter_net_inspector

A Dio interceptor that captures your Flutter app's HTTP traffic and streams it live to the Flutter Net Inspector VSCode extension — with support for mocking responses, setting breakpoints, and replaying requests, all without touching your app code.

Think of it as Flipper/Stetho for Flutter, but the dashboard lives inside VSCode.

The package is safe to leave wired up permanently. When no extension is connected, all requests pass through normally with zero overhead.

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Installation

dependencies:
  flutter_net_inspector: ^0.1.2

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Setup

Step 1 — Add the interceptor to Dio

Wrap your Dio instance with NetInspectorInterceptor in debug mode only:

import 'package:dio/dio.dart';
import 'package:flutter/foundation.dart';
import 'package:flutter_net_inspector/flutter_net_inspector.dart';

final dio = Dio(BaseOptions(baseUrl: 'https://api.example.com'));

if (kDebugMode) {
  final inspector = NetInspectorInterceptor();
  dio.interceptors.insert(0, inspector); // must be first
  inspector.attachDio(dio);              // enables request replay
}

Step 2 — Connect

Call connect() once after your app initialises (e.g. in main() or after your DI container is ready):

void main() async {
  WidgetsFlutterBinding.ensureInitialized();

  if (kDebugMode) {
    await inspector.connect();
  }

  runApp(const MyApp());
}

The client connects in the background and auto-reconnects silently if the extension is not yet running.

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Host configuration

The interceptor needs to reach the WebSocket server run by the VSCode extension (default port 9555). The correct host depends on how you run your app:

Device	Default host	Notes
iOS Simulator	127.0.0.1	Works out of the box
Android Emulator	10.0.2.2	Emulator's alias for the host machine
Android Real Device	—	Set your machine's LAN IP, or use adb reverse
iOS Real Device	—	Set your machine's LAN IP

Override the host

Option A — --dart-define (recommended for teams)

Add to your IDE launch configuration so no shared code changes:

// .vscode/launch.json
{
  "configurations": [
    {
      "name": "Flutter (debug)",
      "type": "dart",
      "request": "launch",
      "args": ["--dart-define=INSPECTOR_HOST=192.168.1.42"]
    }
  ]
}

Or from the terminal:

flutter run --dart-define=INSPECTOR_HOST=192.168.1.42

Option B — set it in code

NetInspectorConfig.host = '192.168.1.42'; // set before constructing the interceptor

Option C — adb reverse (Android real device, no IP needed)

adb reverse tcp:9555 tcp:9555
# host remains 127.0.0.1

Override the port

NetInspectorConfig.port = 9555; // default; change if the extension uses a different port

Or via --dart-define:

flutter run --dart-define=INSPECTOR_PORT=9555

---

Using with a DI container (get_it / injectable)

@module
abstract class NetworkModule {
  @singleton
  NetInspectorInterceptor get inspector => NetInspectorInterceptor();

  @singleton
  Dio dio(NetInspectorInterceptor inspector) {
    final dio = Dio(BaseOptions(baseUrl: Env.apiBaseUrl));
    if (kDebugMode) {
      dio.interceptors.insert(0, inspector);
      inspector.attachDio(dio);
    }
    return dio;
  }
}

// In main(), after getIt is ready:
if (kDebugMode) {
  await getIt<NetInspectorInterceptor>().connect();
}

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What you get in the VSCode dashboard

• Live traffic — every request and response, with headers, body, status, and timing
• Mock responses — intercept any URL and return a custom status, headers, and body
• Breakpoints — pause a response mid-flight, inspect and edit it, then resume
• Replay — re-fire any captured request with one click
• Filters — filter by URL, method, or status code; dedicated views for mocked and errored requests

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Screenshots

Step 1 — Capture traffic and open the context menu

Click the three-dots icon on any captured request to mock it, replay it, or copy it as a cURL command.

Step 2 — Configure the mock response

The mock editor opens pre-filled with the request's URL, method, status code, and response body. Change only what you need.

Step 3 — Mock active

The request is now intercepted. The row is highlighted, the detail panel shows the mocked response body, and your Flutter app receives the mock data.

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Companion

This package requires the Flutter Net Inspector VSCode extension to display the dashboard. Install it from the VS Code Marketplace or from open-vsx.