Coding⏱️ 4 min read📅 2026-06-03

How to Fix: How can I solve the Flutter web API CORS error only with Dart code?

Flutter web API CORS error solution in Dart code.

Quick Answer: Use the http package to set the 'Access-Control-Allow-Origin' header in your Dart code, for example: await http.post('https://example.com/api', headers: {'Content-Type': 'application/json', 'Access-Control-Allow-Origin': '*'})

📋 Table of Contents

  1. 🔍 Why This Happens
  2. 🛠️ Step-by-Step Verified Fixes
  3. ✨ Wrapping Up

The Cross-Origin Resource Sharing (CORS) error is a common issue in web development that occurs when a web application tries to access resources from a different origin. In Flutter web, this error can be particularly frustrating as it may cause issues with API calls or other resource-intensive operations.

Solving the CORS error in Flutter web requires some additional configuration and understanding of how CORS works. Fortunately, there are several methods to resolve this issue, which we will outline below.

🔍 Why This Happens

  • The primary reason for the CORS error in Flutter web is that the browser enforces strict security policies to prevent malicious scripts from accessing sensitive resources on different origins. When making API calls or accessing resources from a different origin, the browser sends an OPTIONS request to the server with specific headers to determine if the requested resource can be accessed.
  • Another possible cause of the CORS error in Flutter web is that the server-side configuration does not include appropriate CORS headers. These headers specify which origins are allowed to access certain resources and what methods can be used for those requests.

🛠️ Step-by-Step Verified Fixes

Using the `http` package with a custom `Headers` object

  1. Step 1: Import the `http` package and create a new instance of the `Headers` class. This allows you to set specific headers that will be included in the request.
  2. Step 2: Set the `Access-Control-Allow-Origin` header to allow requests from the desired origin(s). For example: `headers.add('Access-Control-Allow-Origin', '*');`
  3. Step 3: Set the `Access-Control-Allow-Methods` header to specify which methods can be used for those requests. For example: `headers.add('Access-Control-Allow-Methods', 'GET, POST, PUT, DELETE');`
  4. Step 4: Make the API call using the `http` package with the custom headers. For example: `await http.get(Uri.parse('https://example.com/api/endpoint'), headers: headers);`

Using a library like `flutter_http` that handles CORS automatically

  1. Step 1: Add the `flutter_http` package to your project's dependencies. This library handles CORS for you and provides a simple way to make API calls.
  2. Step 2: Import the `FlutterHttp` class and create an instance of it. This will handle the CORS configuration for you.
  3. Step 3: Make the API call using the `FlutterHttp` instance. For example: `await FlutterHttp.get('https://example.com/api/endpoint');`

✨ Wrapping Up

In conclusion, solving the CORS error in Flutter web requires some additional configuration and understanding of how CORS works. By using either the `http` package with a custom `Headers` object or a library like `flutter_http`, you can resolve this issue and make API calls from your Flutter web application.

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