Decision guide

JSON libraries for .NET

Most new .NET applications should start by checking whether System.Text.Json covers their requirements. Newtonsoft.Json remains a pragmatic choice when its mature feature set, established converters or existing models are part of the project.

The decision to make

Should a new project use System.Text.Json or Newtonsoft.Json?

Target frameworks and whether the library is included in the shared framework.
Required serializer behavior: polymorphism, reference handling, custom converters and DOM APIs.
The migration cost of existing attributes, converters and tests.
Whether package dependencies or source-generation support matter for the deployment model.

Shortlist and trade-offs

These options are starting points, not an exhaustive market list. Verify the current release, compatibility, license and advisory information for your project on the linked package pages.

System.Text.Json

The JSON stack built into modern .NET, with source generation and a low-allocation design.

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Best fit: New .NET applications that target modern runtimes and can use its supported serializer model.
Validate first: Check behavior differences before migrating Newtonsoft.Json attributes, converters or reference handling.

Newtonsoft.Json

A long-established JSON library with a broad converter and compatibility ecosystem.

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Best fit: Existing applications or integrations that already depend on Json.NET behavior and extension points.
Validate first: It adds a package dependency where System.Text.Json may already be available in the runtime.

JsonSchema.Net

A focused library for evaluating JSON Schema rather than replacing an application serializer.

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Best fit: Validating JSON contracts at boundaries, configuration inputs or integration points.
Validate first: It complements a serializer; it is not a general System.Text.Json or Json.NET alternative.

When to revisit this choice

Re-evaluate the choice when changing target frameworks, introducing Native AOT, or integrating an API with a fixed JSON contract.

Data, method and limits

Sources: the public NuGet v3 registry and NuBrowse editorial review. Refresh: package pages read current registry metadata when viewed; guide text is revised separately. Method: the shortlist favours distinct use cases and spells out trade-offs instead of calculating a quality score. Limit: validate the specific version, license, framework and operational requirements in your project.