stj-serialization-optimizer

System.Text.Json Optimizer

Make JSON serialization faster and leaner with System.Text.Json — source generation, reused options, streaming, and the small mistakes that cost a lot.

Input — point it at your code

Works on a target: a file, folder, project, or GitHub URL. Find usage: grep -rn "JsonSerializer\.\|JsonSerializerOptions\|System.Text.Json" --include=*.cs <target>.

Top fixes

1. Reuse JsonSerializerOptions — building a new options object per call is expensive (it caches metadata). Create one static instance and reuse it. This alone is a common big win.
2. Source generation — avoid reflection at runtime with a JsonSerializerContext:

[JsonSerializable(typeof(Order))]
[JsonSerializable(typeof(List<Order>))]
public partial class AppJsonContext : JsonSerializerContext { }

var json = JsonSerializer.Serialize(order, AppJsonContext.Default.Order);

Faster startup, lower allocations, AOT-friendly. 3. Stream, don't buffer — JsonSerializer.SerializeAsync(stream, ...) / DeserializeAsync for large payloads and HTTP bodies instead of Serialize to a string then write. 4. Utf8JsonWriter/Utf8JsonReader for the hottest custom paths — work on byte/UTF-8 directly, skip the string. 5. Trim the payload — [JsonIgnore], DefaultIgnoreCondition = WhenWritingNull, shorter property names where appropriate. 6. Custom converters only when needed — and make them allocation-light.

Principles

• Options reuse + source generation are 80% of the wins — do those first.
• Stream large payloads; don't materialize giant strings.
• Measure with [MemoryDiagnoser] — serialization is often an allocation story.
• Don't hand-roll converters the built-in serializer already handles.

How to use it & best prompts

"Speed up my JSON serialization", "add System.Text.Json source generation", "why does serializing this allocate so much", "stream this large JSON response". Pairs with benchmarkdotnet-setup.