Serialization benchmarks

BENCHMARKS · SERIALIZATION

System.Text.Json (reflection and source-gen) vs Newtonsoft, both directions. Suite and raw reports: github.com/gdhami-net/dotnet-benchmarks.

Intel Core Ultra 9 285HX · Windows 11 · BenchmarkDotNet 0.15.8 · SDK 10.0.201 · 2026-09-01 · median of 4 quiet runs · typical spread ±3.3% · bars/tables: mean time, lower is better

SerializeOrders

Serialize the same order list three ways: reflection-based System.Text.Json, its source-generated twin, and Newtonsoft.Json.

TAKEAWAY Turn on the source generator: same API, same output, roughly a quarter faster and AOT-safe. Keep Newtonsoft only where its features (converters, LINQ-to-JSON) are actually used.
In this run: Stj_sourcegen is fastest — 1.5× faster than the baseline.

RESULTS — 100

method	net9.0	net10.0	ratio	allocated	Δ net10.0
Stj_reflection baseline	16.9 µs ±142 ns	15.1 µs ±129 ns	1.00×	21.7 KB	-11%
Stj_sourcegen	12.3 µs ±100 ns	10.0 µs ±79 ns	0.66×	21.4 KB	-19%
Newtonsoft_json	34.3 µs ±193 ns	31.1 µs ±319 ns	2.06×	70.0 KB	-10%

RATIO VS BASELINE — 100 · net10.0

Stj_reflection1.00×

Stj_sourcegen0.66×

Newtonsoft_json2.06×

RESULTS — 10000

method	net9.0	net10.0	ratio	allocated	Δ net10.0
Stj_reflection baseline	2.11 ms ±17.3 µs	1.90 ms ±14.0 µs	1.00×	2.13 MB	-10%
Stj_sourcegen	1.76 ms ±9.0 µs	1.48 ms ±21.2 µs	0.78×	2.13 MB	-16%
Newtonsoft_json	4.28 ms ±66.1 µs	3.94 ms ±61.9 µs	2.07×	5.80 MB	-8%

RATIO VS BASELINE — 10000 · net10.0

Stj_reflection1.00×

Stj_sourcegen0.78×

Newtonsoft_json2.07×

SCALING · net10.0 · MEAN TIME BY INPUT SIZE (LOG)

Stj_reflectionStj_sourcegenNewtonsoft_json

THE LEDGER · SAME WORKLOAD ACROSS RELEASES (LOG)

Stj_reflectionStj_sourcegenNewtonsoft_json

THE CODE BEING MEASURED

Stj_reflection — what this measures

System.Text.Json with reflection-driven metadata — the default most codebases run.

[Benchmark (Baseline)]
public string Stj_reflection()
=> JsonSerializer.Serialize(_orders);

Stj_sourcegen — what this measures

System.Text.Json with compile-time source-generated metadata — no runtime reflection.

[Benchmark]
public string Stj_sourcegen()
=> JsonSerializer.Serialize(_orders, OrderJsonContext.Default.ListOrder);

Newtonsoft_json — what this measures

Newtonsoft.Json — the library much of .NET migrated from.

[Benchmark]
public string Newtonsoft_json()
=> Newtonsoft.Json.JsonConvert.SerializeObject(_orders);

DeserializeOrders

Read the same JSON back: reflection vs source-generated System.Text.Json vs Newtonsoft.

TAKEAWAY Deserialization is where serializer choice hurts most - it runs on every request you receive. Source-gen System.Text.Json is the default to standardize on.
In this run: Stj_sourcegen is fastest — 1.0× faster than the baseline.

RESULTS — 100

method	net9.0	net10.0	ratio	allocated	Δ net10.0
Stj_reflection baseline	36.8 µs ±223 ns	34.1 µs ±264 ns	1.00×	42.5 KB	-7%
Stj_sourcegen	37.2 µs ±239 ns	33.5 µs ±285 ns	0.98×	42.5 KB	-10%
Newtonsoft_json	58.3 µs ±291 ns	51.8 µs ±418 ns	1.52×	96.1 KB	-11%

RATIO VS BASELINE — 100 · net10.0

Stj_reflection1.00×

Stj_sourcegen0.98×

Newtonsoft_json1.52×

RESULTS — 10000

method	net9.0	net10.0	ratio	allocated	Δ net10.0
Stj_reflection baseline	4.63 ms ±86.2 µs	4.43 ms ±141.9 µs	1.00×	4.16 MB	-4%
Stj_sourcegen	4.60 ms ±119.2 µs	4.39 ms ±134.4 µs	0.99×	4.16 MB	-5%
Newtonsoft_json	7.44 ms ±164.0 µs	6.77 ms ±110.7 µs	1.53×	9.19 MB	-9%

RATIO VS BASELINE — 10000 · net10.0

Stj_reflection1.00×

Stj_sourcegen0.99×

Newtonsoft_json1.53×

SCALING · net10.0 · MEAN TIME BY INPUT SIZE (LOG)

Stj_reflectionStj_sourcegenNewtonsoft_json

THE LEDGER · SAME WORKLOAD ACROSS RELEASES (LOG)

Stj_reflectionStj_sourcegenNewtonsoft_json

THE CODE BEING MEASURED

Stj_reflection — what this measures

System.Text.Json, reflection-driven metadata.

[Benchmark (Baseline)]
public List<Order>? Stj_reflection()
=> JsonSerializer.Deserialize<List<Order>>(_json);

Stj_sourcegen — what this measures

System.Text.Json, source-generated metadata.

[Benchmark]
public List<Order>? Stj_sourcegen()
=> JsonSerializer.Deserialize(_json, OrderJsonContext.Default.ListOrder);

Newtonsoft_json — what this measures

Newtonsoft.Json.

[Benchmark]
public List<Order>? Newtonsoft_json()
=> Newtonsoft.Json.JsonConvert.DeserializeObject<List<Order>>(_json);

speed vs allocation

Fast is one axis. What it costs the GC is the other.

Stj_reflectionStj_sourcegenNewtonsoft_jsonStj_reflectionStj_sourcegenNewtonsoft_json