> ## Documentation Index
> Fetch the complete documentation index at: https://ancplua.mintlify.site/llms.txt
> Use this file to discover all available pages before exploring further.

# AL0027 - Avoid legacy JSON library

> Replace legacy JSON libraries with System.Text.Json for better performance and native .NET support

Source: [AL0027AvoidNewtonsoftJsonAnalyzer.cs](https://github.com/ANcpLua/ANcpLua.Analyzers/blob/main/src/ANcpLua.Analyzers/Analyzers/AL0027AvoidNewtonsoftJsonAnalyzer.cs)

## Description

The legacy JSON library (Newtonsoft.Json) should be replaced with System.Text.Json for better performance and native .NET support.

This rule only triggers when System.Text.Json is available in the project, making migration possible.

## Bad Code

```csharp theme={null}
using Newtonsoft.Json;

var json = JsonConvert.SerializeObject(obj);
var obj = JsonConvert.DeserializeObject<MyClass>(json);
var jObject = JObject.Parse(json);
```

## Good Code

```csharp theme={null}
using System.Text.Json;

var json = JsonSerializer.Serialize(obj);
var obj = JsonSerializer.Deserialize<MyClass>(json);
var doc = JsonDocument.Parse(json);
```

## Properties

* **Category**: Usage
* **Severity**: Warning
* **Enabled by default**: True
* **Code fix available**: False

## Configuration

```editorconfig theme={null}
dotnet_diagnostic.AL0027.severity = warning
```

## Notes

System.Text.Json is the recommended JSON library for .NET applications. It offers:

* Better performance (faster serialization/deserialization)
* Lower memory allocations
* Native integration with ASP.NET Core
* Source generator support for AOT compilation