update llms.txt file for System.Text.Json

docs/standard/serialization/system-text-json/llms.txt

@@ -2,38 +2,26 @@
 
 > High-performance JSON serialization and deserialization for .NET applications.
 
-*Topics available: 31*
-
-**.NET 10 adds:** `JsonSerializerOptions.Strict` preset for best-practice defaults, `AllowDuplicateProperties` option to reject duplicate JSON properties, `PipeReader` deserialization support, and `ReferenceHandler` in `JsonSourceGenerationOptions`.
-
-- [Serialize and deserialize JSON using C#](https://raw.githubusercontent.com/dotnet/docs/refs/heads/llmstxt/docs/standard/serialization/system-text-json/overview.md): This overview describes the System.Text.Json namespace functionality for serializing to and deserializing from JSON in .NET.
-- [How to serialize JSON in C#](https://raw.githubusercontent.com/dotnet/docs/refs/heads/llmstxt/docs/standard/serialization/system-text-json/how-to.md): Learn how to use the System.Text.Json namespace to serialize to JSON in .NET. Includes sample code.
-- [Migrate from Newtonsoft.Json to System.Text.Json](https://raw.githubusercontent.com/dotnet/docs/refs/heads/llmstxt/docs/standard/serialization/system-text-json/migrate-from-newtonsoft.md): Learn about the differences between Newtonsoft.Json and System.Text.Json and how to migrate to System.Text.Json.
-- [How to enable case-insensitive property name matching with System.Text.Json](https://raw.githubusercontent.com/dotnet/docs/refs/heads/llmstxt/docs/standard/serialization/system-text-json/character-casing.md): Learn how to enable case-insensitive property name matching while serializing to and deserializing from JSON in .NET.
-- [How to customize character encoding with System.Text.Json](https://raw.githubusercontent.com/dotnet/docs/refs/heads/llmstxt/docs/standard/serialization/system-text-json/character-encoding.md): Learn how to customize character encoding while serializing to and deserializing from JSON in .NET.
-- [How to instantiate JsonSerializerOptions with System.Text.Json](https://raw.githubusercontent.com/dotnet/docs/refs/heads/llmstxt/docs/standard/serialization/system-text-json/configure-options.md): Learn about constructors for JsonSerializerOptions instances and how to reuse JsonSerializerOptions instances.
-- [How to write custom converters for JSON serialization](https://raw.githubusercontent.com/dotnet/docs/refs/heads/llmstxt/docs/standard/serialization/system-text-json/converters-how-to.md): Learn how to create custom converters for the JSON serialization classes that are provided in the System.Text.Json namespace.
-- [Custom serialization and deserialization contracts](https://raw.githubusercontent.com/dotnet/docs/refs/heads/llmstxt/docs/standard/serialization/system-text-json/custom-contracts.md): Learn how to write your own contract resolution logic to customize the JSON contract for a type.
-- [How to customize property names and values with System.Text.Json](https://raw.githubusercontent.com/dotnet/docs/refs/heads/llmstxt/docs/standard/serialization/system-text-json/customize-properties.md): Learn how to customize property names and values when serializing with System.Text.Json in .NET.
-- [How to deserialize JSON in C#](https://raw.githubusercontent.com/dotnet/docs/refs/heads/llmstxt/docs/standard/serialization/system-text-json/deserialization.md): Learn how to use the System.Text.Json namespace to deserialize from JSON in .NET. Includes sample code.
-- [JSON schema exporter](https://raw.githubusercontent.com/dotnet/docs/refs/heads/llmstxt/docs/standard/serialization/system-text-json/extract-schema.md): Learn how to use the JsonSchemaExporter class to extract JSON schema documents from .NET types.
-- [Include fields in serialization](https://raw.githubusercontent.com/dotnet/docs/refs/heads/llmstxt/docs/standard/serialization/system-text-json/fields.md): Learn how to include fields when you serialize to and deserialize from JSON in .NET.
-- [How to handle overflow JSON or use JsonElement or JsonNode in System.Text.Json](https://raw.githubusercontent.com/dotnet/docs/refs/heads/llmstxt/docs/standard/serialization/system-text-json/handle-overflow.md): Learn how to handle overflow JSON or use JsonElement or JsonNode while using System.Text.Json to serialize and deserialize JSON in .NET.
-- [Serialization extension methods on HttpClient](https://raw.githubusercontent.com/dotnet/docs/refs/heads/llmstxt/docs/standard/serialization/system-text-json/httpclient-extensions.md): Learn how to serialize and deserialize JSON payloads from the network in a single line of code using extension methods on HttpClient and HttpContent.
-- [How to ignore properties with System.Text.Json](https://raw.githubusercontent.com/dotnet/docs/refs/heads/llmstxt/docs/standard/serialization/system-text-json/ignore-properties.md): Learn how to ignore properties when serializing with System.Text.Json in .NET.
-- [Use immutable types and properties](https://raw.githubusercontent.com/dotnet/docs/refs/heads/llmstxt/docs/standard/serialization/system-text-json/immutability.md): Learn how to deserialize JSON to immutable types and properties in .NET.
-- [How to allow some kinds of invalid JSON with System.Text.Json](https://raw.githubusercontent.com/dotnet/docs/refs/heads/llmstxt/docs/standard/serialization/system-text-json/invalid-json.md): Learn how to allow comments, trailing commas, and quoted numbers while serializing to and deserializing from JSON in .NET.
-- [Handle unmapped members during deserialization](https://raw.githubusercontent.com/dotnet/docs/refs/heads/llmstxt/docs/standard/serialization/system-text-json/missing-members.md): Learn how to configure the JSON deserialization behavior when properties are present in the JSON payload that aren't present in the POCO type.
-- [Respect nullable annotations](https://raw.githubusercontent.com/dotnet/docs/refs/heads/llmstxt/docs/standard/serialization/system-text-json/nullable-annotations.md): Learn how to configure serialization and deserialization to respect nullable annotations.
-- [How to serialize properties of derived classes with System.Text.Json](https://raw.githubusercontent.com/dotnet/docs/refs/heads/llmstxt/docs/standard/serialization/system-text-json/polymorphism.md): Learn how to serialize polymorphic objects while serializing to and deserializing from JSON in .NET.
-- [Populate initialized properties](https://raw.githubusercontent.com/dotnet/docs/refs/heads/llmstxt/docs/standard/serialization/system-text-json/populate-properties.md): Learn how to modify properties and fields that are already initialized when deserializing from JSON in .NET.
-- [How to preserve references in System.Text.Json](https://raw.githubusercontent.com/dotnet/docs/refs/heads/llmstxt/docs/standard/serialization/system-text-json/preserve-references.md): Learn how to preserve references and handle or ignore circular references while using System.Text.Json to serialize and deserialize JSON in .NET.
-- [How to choose reflection or source generation in System.Text.Json](https://raw.githubusercontent.com/dotnet/docs/refs/heads/llmstxt/docs/standard/serialization/system-text-json/reflection-vs-source-generation.md): Learn how to choose reflection or source generation in System.Text.Json.
-- [Require properties for deserialization](https://raw.githubusercontent.com/dotnet/docs/refs/heads/llmstxt/docs/standard/serialization/system-text-json/required-properties.md): Learn how to mark properties as required for deserialization to succeed.
-- [Source-generation modes in System.Text.Json](https://raw.githubusercontent.com/dotnet/docs/refs/heads/llmstxt/docs/standard/serialization/system-text-json/source-generation-modes.md): Learn about the two different source-generation modes in System.Text.Json.
-- [How to use source generation in System.Text.Json](https://raw.githubusercontent.com/dotnet/docs/refs/heads/llmstxt/docs/standard/serialization/system-text-json/source-generation.md): Learn how to use source generation in System.Text.Json.
-- [Supported types in System.Text.Json](https://raw.githubusercontent.com/dotnet/docs/refs/heads/llmstxt/docs/standard/serialization/system-text-json/supported-types.md): Learn which types are supported for serialization by the APIs in the System.Text.Json namespace.
-- [How to use a JSON DOM in System.Text.Json](https://raw.githubusercontent.com/dotnet/docs/refs/heads/llmstxt/docs/standard/serialization/system-text-json/use-dom.md): Learn how to use a JSON document object model (DOM).
-- [How to use Utf8JsonReader in System.Text.Json](https://raw.githubusercontent.com/dotnet/docs/refs/heads/llmstxt/docs/standard/serialization/system-text-json/use-utf8jsonreader.md): Learn how to use Utf8JsonReader.
-- [How to use Utf8JsonWriter in System.Text.Json](https://raw.githubusercontent.com/dotnet/docs/refs/heads/llmstxt/docs/standard/serialization/system-text-json/use-utf8jsonwriter.md): Learn how to use Utf8JsonWriter.
-- [Visual Basic support for System.Text.Json](https://raw.githubusercontent.com/dotnet/docs/refs/heads/llmstxt/docs/standard/serialization/system-text-json/visual-basic-support.md): Learn which parts of the System.Text.Json namespace aren't supported in Visual Basic.
+## What's New in .NET 10
+
+### New APIs
+
+- `JsonSerializerOptions.Strict` / `JsonSerializerDefaults.Strict` — best-practice preset that disallows unmapped members, duplicate properties, and enforces nullable annotations.
+- `JsonSerializerOptions.AllowDuplicateProperties` — option to reject duplicate JSON keys (disabled in Strict).
+- `JsonSerializer.DeserializeAsync<T>(PipeReader)` — direct PipeReader deserialization without Stream conversion.
+- `JsonSourceGenerationOptionsAttribute.ReferenceHandler` — specify ReferenceHandler in source-generated contexts to handle circular references.
+
+For full details and code examples, see: [.NET 10 Serialization update](https://github.com/dotnet/docs/blob/main/docs/core/whats-new/dotnet-10/libraries.md#serialization).
+
+### Breaking Changes
+
+- **Property name conflict validation** — System.Text.Json now validates that user-defined property names don't conflict with metadata property names (`$type`, `$id`, `$ref`, or custom `TypeDiscriminatorPropertyName`). Previously, conflicts silently produced invalid JSON with duplicate properties; now an `InvalidOperationException` is thrown. Rename the conflicting property or apply `[JsonIgnore]` to resolve.
+
+For details, see: [System.Text.Json checks for property name conflicts](https://github.com/dotnet/docs/blob/main/docs/core/compatibility/serialization/10/property-name-validation.md).
+
+## Best Practices
+
+- **Reuse `JsonSerializerOptions` instances.** Creating a new instance per call is expensive — the metadata cache is rebuilt each time. Use a shared static instance or the built-in singletons (`JsonSerializerOptions.Default`, `.Web`, `.Strict`).
+- **Use source generation for AOT/trimming.** Reflection-based serialization is incompatible with Native AOT. Use `[JsonSerializable]` attribute to the context classes for AOT-safe serialization. See the source generation topic below.
+- **Prefer `Strict` for new projects.** The `Strict` preset catches common mistakes (unmapped members, duplicate keys, null violations) at deserialization time rather than silently ignoring them.
+- **Serialize to UTF-8 when possible.** `SerializeToUtf8Bytes()` is 5–10% faster than string-based serialization because it avoids UTF-16 conversion.