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 · 2026-08-22 · single run — not yet median-of-N · 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	16.1 µs ±156 ns	15.2 µs ±857 ns	1.00×	21.7 KB	-6%
Stj_sourcegen	12.7 µs ±1.0 µs	10.1 µs ±752 ns	0.67×	21.4 KB	-20%
Newtonsoft_json	33.2 µs ±269 ns	30.6 µs ±382 ns	2.02×	70.0 KB	-8%

RATIO VS BASELINE — 100 · net10.0

Stj_reflection

1.00×

Stj_sourcegen

0.67×

Newtonsoft_json

2.02×

RESULTS — 10000

method	net9.0	net10.0	ratio	allocated	Δ net10.0
Stj_reflection baseline	2.18 ms ±26.0 µs	1.95 ms ±41.0 µs	1.00×	2.18 MB	-11%
Stj_sourcegen	1.77 ms ±36.1 µs	1.50 ms ±33.5 µs	0.77×	2.17 MB	-15%
Newtonsoft_json	4.30 ms ±114.6 µs	3.88 ms ±52.2 µs	1.99×	5.80 MB	-10%

RATIO VS BASELINE — 10000 · net10.0

Stj_reflection

1.00×

Stj_sourcegen

0.77×

Newtonsoft_json

1.99×

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	35.8 µs ±144 ns	34.9 µs ±1.4 µs	1.00×	42.5 KB	-2%
Stj_sourcegen	37.4 µs ±1.5 µs	34.0 µs ±1.9 µs	0.97×	42.5 KB	-9%
Newtonsoft_json	59.1 µs ±3.0 µs	52.0 µs ±2.8 µs	1.49×	96.1 KB	-12%

RATIO VS BASELINE — 100 · net10.0

Stj_reflection

1.00×

Stj_sourcegen

0.97×

Newtonsoft_json

1.49×

RESULTS — 10000

method	net9.0	net10.0	ratio	allocated	Δ net10.0
Stj_reflection baseline	4.89 ms ±406.0 µs	4.31 ms ±262.0 µs	1.00×	4.16 MB	-12%
Stj_sourcegen	4.52 ms ±112.7 µs	4.45 ms ±324.2 µs	1.03×	4.19 MB	-2%
Newtonsoft_json	7.47 ms ±412.7 µs	6.57 ms ±244.1 µs	1.52×	9.19 MB	-12%

RATIO VS BASELINE — 10000 · net10.0

Stj_reflection

1.00×

Stj_sourcegen

1.03×

Newtonsoft_json

1.52×

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