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.

4 criteria3 packages4-point checklist

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.

Inspect package

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.

Inspect package

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.

Inspect package

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.

Practical implementation plan

1Start with a small, representative feature and validate the package against the actual target framework and deployment environment.
2Write contract-focused tests for the required behavior before rolling the choice across the solution.
3Document package version, configuration, operational ownership, and an explicit rollback plan in the change record.

Common pitfalls

Choosing by popularity alone instead of validating compatibility, maintenance posture, and the application's actual constraints.
Adding overlapping packages that solve the same concern, increasing upgrade and incident-response effort.
Shipping default configuration without validating security, performance, and operational behavior in the deployed environment.

Before production

The selected package version is compatible with supported target frameworks.
Configuration is reviewed for security, observability, and production defaults.
Representative success and failure paths are covered by automated tests.
License, advisory, and upgrade ownership are recorded for the dependency.

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.

Put this decision into practice

Audit NuGet dependencies in a .NET project Review NuGet licenses before shipping Audit Central Package Management versions

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.