🥚 EggMapper

The fastest .NET runtime object-to-object mapper — forked from AutoMapper's last open-source release, rebuilt for maximum performance. Drop-in replacement with the same API, 1.5–5× faster.

Overview

EggMapper started as a fork of AutoMapper's last open-source release and was completely rewritten for performance. It keeps the same familiar API — MapperConfiguration, CreateMap, ForMember, Profile, IMapper — so you can switch from AutoMapper with minimal code changes. Under the hood, it compiles expression-tree delegates with inlined nested maps, typed collection loops, and static generic caching, achieving zero reflection at map-time, zero extra allocations, and near-manual mapping speed.

Migrating from AutoMapper?

EggMapper is a drop-in replacement. In most cases, you only need to:

Replace using AutoMapper; with using EggMapper;
Replace services.AddAutoMapper(...) with services.AddEggMapper(...)

The same CreateMap<>(), ForMember(), ReverseMap(), Profile, and IMapper APIs work identically.

Why EggMapper?

🚀 Faster than Mapster on flat, flattening, deep, and complex mappings
🔥 1.5–5× faster than AutoMapper across all scenarios
🎯 Zero extra allocations — matches hand-written code exactly
🔁 Drop-in AutoMapper replacement — same fluent API, same patterns
🧩 Full feature set — profiles, ForMember, ReverseMap, nested types, collections, DI, and more
🪶 Lightweight — no runtime reflection, no unnecessary allocations
📖 MIT licensed — free for commercial use, forever

Installation

dotnet add package EggMapper

DI support (AddEggMapper) is included in the main package — no separate package needed.

Quick Start

using EggMapper;

var config = new MapperConfiguration(cfg => {
    cfg.CreateMap<Source, Destination>();
});

var mapper = config.CreateMapper();
var dest = mapper.Map<Destination>(source);

With Profiles

public class MyProfile : Profile
{
    public MyProfile()
    {
        CreateMap<Customer, CustomerDto>()
            .ForMember(d => d.FullName, opt => opt.MapFrom(s => $"{s.FirstName} {s.LastName}"))
            .ForMember(d => d.AddressLine, opt => opt.MapFrom(s => s.Address.Street));
    }
}

var config = new MapperConfiguration(cfg => cfg.AddProfile<MyProfile>());
var mapper = config.CreateMapper();

Dependency Injection

// In Program.cs
builder.Services.AddEggMapper(typeof(MyProfile).Assembly);

// In your service
public class MyService(IMapper mapper) { ... }

Performance

⏱ Last updated: 2026-05-22 15:12 UTC

All benchmarks run on BenchmarkDotNet with .NET 10. Ratio = time vs hand-written manual code (lower is better).

Scenario	Manual	EggMapper	Mapster	AutoMapper	Mapperly*
Flat (10 props)	16.15 ns	29.01 ns (1.8×)	28.16 ns (1.7×)	80.39 ns (5.0×)	17.14 ns (1.1×)
Flattening	20.73 ns	31.25 ns (1.5×)	34.24 ns (1.6×)	84.05 ns (4.0×)	24.53 ns (1.2×)
Deep (2 nested)	56.27 ns	69.58 ns (1.2×)	73.01 ns (1.3×)	108.09 ns (1.9×)	52.90 ns (0.9×)
Complex (nest+coll)	88.16 ns	105.17 ns (1.2×)	100.13 ns (1.1×)	145.32 ns (1.6×)	80.72 ns (0.9×)
Collection (100)	2.208 μs	2.095 μs (0.9×)	2.058 μs (0.9×)	2.641 μs (1.2×)	2.156 μs (1.0×)
Deep Coll (100)	5.985 μs	6.458 μs (1.1×)	6.416 μs (1.1×)	7.090 μs (1.2×)	5.878 μs (1.0×)
Large Coll (1000)	21.52 μs	20.78 μs (1.0×)	21.46 μs (1.0×)	25.36 μs (1.2×)	22.22 μs (1.0×)

* Mapperly is a compile-time source generator — it produces code equivalent to hand-written mapping. EggMapper is the fastest runtime mapper.

Allocations: EggMapper matches manual allocation exactly in every scenario (zero extra bytes).

Run the benchmarks yourself:

cd src/EggMapper.Benchmarks
dotnet run --configuration Release -f net10.0 -- --filter * --exporters json markdown

Competitors tested: EggMapper, AutoMapper, Mapster, Mapperly (source-gen), AgileMapper

Column guide: Mean = avg time · Error = ½ CI · StdDev = std dev · Min/Median/Max = range · Ratio = vs Manual baseline · Rank = 1 is fastest · Allocated = heap / op

🔵 Flat Mapping (10 properties)

Method	Mean	Error	StdDev	Min	Median	Max	Ratio	RatioSD	Rank	Gen0	Allocated	Alloc Ratio
Manual	16.15 ns	0.273 ns	0.242 ns	15.71 ns	16.21 ns	16.42 ns	1.00	0.02	1	0.0048	80 B	1.00
EggMapper	29.01 ns	0.282 ns	0.264 ns	28.57 ns	28.99 ns	29.38 ns	1.80	0.03	2	0.0048	80 B	1.00
AutoMapper	80.39 ns	0.074 ns	0.061 ns	80.29 ns	80.41 ns	80.47 ns	4.98	0.07	3	0.0048	80 B	1.00
Mapster	28.16 ns	0.424 ns	0.397 ns	27.62 ns	28.22 ns	28.88 ns	1.74	0.03	2	0.0048	80 B	1.00
MapperlyMap	17.14 ns	0.397 ns	0.407 ns	16.02 ns	17.21 ns	17.68 ns	1.06	0.03	1	0.0048	80 B	1.00
AgileMapper	372.54 ns	1.937 ns	1.812 ns	368.55 ns	372.64 ns	374.88 ns	23.08	0.35	4	0.0205	344 B	4.30
EggMapperGenerator	16.26 ns	0.172 ns	0.143 ns	16.07 ns	16.25 ns	16.63 ns	1.01	0.02	1	0.0048	80 B	1.00
EggMapperClassMapper	16.96 ns	0.322 ns	0.301 ns	16.44 ns	16.95 ns	17.44 ns	1.05	0.02	1	0.0048	80 B	1.00

🟡 Flattening

Method	Mean	Error	StdDev	Min	Median	Max	Ratio	RatioSD	Rank	Gen0	Allocated	Alloc Ratio
Manual	20.73 ns	0.193 ns	0.180 ns	20.32 ns	20.73 ns	21.03 ns	1.00	0.01	1	0.0048	80 B	1.00
EggMap	31.25 ns	0.297 ns	0.263 ns	30.94 ns	31.23 ns	31.88 ns	1.51	0.02	3	0.0048	80 B	1.00
AutoMapper	84.05 ns	0.361 ns	0.320 ns	83.72 ns	83.89 ns	84.53 ns	4.05	0.04	5	0.0048	80 B	1.00
Mapster	34.24 ns	0.383 ns	0.359 ns	33.82 ns	34.15 ns	34.98 ns	1.65	0.02	4	0.0048	80 B	1.00
MapperlyMap	24.53 ns	0.397 ns	0.371 ns	24.09 ns	24.47 ns	25.18 ns	1.18	0.02	2	0.0062	104 B	1.30
AgileMapper	325.54 ns	2.157 ns	1.912 ns	323.15 ns	325.18 ns	330.02 ns	15.70	0.16	6	0.0205	344 B	4.30

🟣 Deep Mapping (2 nested objects)

Method	Mean	Error	StdDev	Min	Median	Max	Ratio	RatioSD	Rank	Gen0	Allocated	Alloc Ratio
Manual	56.27 ns	0.099 ns	0.083 ns	56.14 ns	56.25 ns	56.40 ns	1.00	0.00	2	0.0162	272 B	1.00
EggMapper	69.58 ns	0.303 ns	0.269 ns	69.11 ns	69.50 ns	69.98 ns	1.24	0.00	3	0.0162	272 B	1.00
AutoMapper	108.09 ns	0.203 ns	0.180 ns	107.82 ns	108.06 ns	108.38 ns	1.92	0.00	5	0.0162	272 B	1.00
Mapster	73.01 ns	0.804 ns	0.752 ns	70.97 ns	73.24 ns	73.86 ns	1.30	0.01	4	0.0162	272 B	1.00
MapperlyMap	52.90 ns	0.270 ns	0.239 ns	52.56 ns	52.86 ns	53.24 ns	0.94	0.00	1	0.0162	272 B	1.00
AgileMapper	358.36 ns	1.869 ns	1.748 ns	354.39 ns	358.28 ns	361.11 ns	6.37	0.03	6	0.0253	424 B	1.56

🟢 Complex Mapping (nested + collection)

Method	Mean	Error	StdDev	Min	Median	Max	Ratio	RatioSD	Rank	Gen0	Allocated	Alloc Ratio
Manual	88.16 ns	0.947 ns	0.886 ns	86.06 ns	88.35 ns	89.58 ns	1.00	0.01	2	0.0191	320 B	1.00
EggMapper	105.17 ns	0.717 ns	0.636 ns	104.08 ns	105.30 ns	106.06 ns	1.19	0.01	4	0.0191	320 B	1.00
AutoMapper	145.32 ns	1.394 ns	1.304 ns	143.47 ns	145.31 ns	147.61 ns	1.65	0.02	5	0.0196	328 B	1.02
Mapster	100.13 ns	0.684 ns	0.640 ns	98.31 ns	100.15 ns	100.98 ns	1.14	0.01	3	0.0191	320 B	1.00
MapperlyMap	80.72 ns	1.258 ns	1.115 ns	77.72 ns	81.16 ns	81.90 ns	0.92	0.02	1	0.0191	320 B	1.00
AgileMapper	405.62 ns	1.279 ns	1.196 ns	403.89 ns	405.46 ns	407.62 ns	4.60	0.05	6	0.0315	528 B	1.65

🟠 Collection (100 items)

Method	Mean	Error	StdDev	Min	Median	Max	Ratio	RatioSD	Rank	Gen0	Gen1	Allocated	Alloc Ratio
Manual	2.208 μs	0.0290 μs	0.0271 μs	2.164 μs	2.215 μs	2.251 μs	1.00	0.02	1	0.5264	0.0153	8.65 KB	1.00
EggMapper	2.095 μs	0.0412 μs	0.0850 μs	1.912 μs	2.090 μs	2.274 μs	0.95	0.04	1	0.5264	0.0153	8.65 KB	1.00
AutoMapper	2.641 μs	0.0527 μs	0.0951 μs	2.497 μs	2.655 μs	2.899 μs	1.20	0.04	2	0.6065	0.0191	9.95 KB	1.15
Mapster	2.058 μs	0.0405 μs	0.0897 μs	1.910 μs	2.059 μs	2.286 μs	0.93	0.04	1	0.5264	0.0153	8.65 KB	1.00
MapperlyMap	2.156 μs	0.0414 μs	0.0539 μs	2.049 μs	2.155 μs	2.265 μs	0.98	0.03	1	0.5264	0.0153	8.65 KB	1.00
AgileMapper	2.722 μs	0.0523 μs	0.0603 μs	2.616 μs	2.709 μs	2.822 μs	1.23	0.03	2	0.5417	0.0153	8.91 KB	1.03

🔴 Deep Collection (100 items, nested)

Method	Mean	Error	StdDev	Min	Median	Max	Ratio	Rank	Gen0	Gen1	Allocated	Alloc Ratio
Manual	5.985 μs	0.0644 μs	0.0571 μs	5.871 μs	5.975 μs	6.086 μs	1.00	2	1.6708	0.0916	27.4 KB	1.00
EggMapper	6.458 μs	0.0696 μs	0.0651 μs	6.338 μs	6.429 μs	6.581 μs	1.08	3	1.6708	0.0916	27.4 KB	1.00
AutoMapper	7.090 μs	0.0181 μs	0.0161 μs	7.065 μs	7.087 μs	7.116 μs	1.18	4	1.7548	0.1068	28.7 KB	1.05
Mapster	6.416 μs	0.0431 μs	0.0403 μs	6.332 μs	6.420 μs	6.492 μs	1.07	3	1.6708	0.0916	27.4 KB	1.00
MapperlyMap	5.878 μs	0.0299 μs	0.0265 μs	5.845 μs	5.867 μs	5.928 μs	0.98	2	1.6785	0.0992	27.42 KB	1.00
AgileMapper	5.628 μs	0.0280 μs	0.0234 μs	5.596 μs	5.631 μs	5.682 μs	0.94	1	1.0223	0.0610	16.72 KB	0.61

⚫ Large Collection (1,000 items)

Method	Mean	Error	StdDev	Min	Median	Max	Ratio	RatioSD	Rank	Gen0	Gen1	Allocated	Alloc Ratio
Manual	21.52 μs	0.183 μs	0.162 μs	21.15 μs	21.58 μs	21.70 μs	1.00	0.01	1	5.2490	1.3123	85.99 KB	1.00
EggMapper	20.78 μs	0.414 μs	0.935 μs	19.46 μs	20.71 μs	23.24 μs	0.97	0.04	1	5.2490	1.3123	85.99 KB	1.00
AutoMapper	25.36 μs	0.503 μs	0.517 μs	24.24 μs	25.46 μs	26.09 μs	1.18	0.02	2	5.7678	1.4343	94.34 KB	1.10
Mapster	21.46 μs	0.426 μs	0.880 μs	20.07 μs	21.31 μs	23.60 μs	1.00	0.04	1	5.2490	1.3123	85.99 KB	1.00
MapperlyMap	22.22 μs	0.442 μs	1.149 μs	20.81 μs	21.90 μs	25.37 μs	1.03	0.05	1	5.2490	1.2817	86.02 KB	1.00
AgileMapper	23.03 μs	0.456 μs	0.823 μs	21.85 μs	22.79 μs	24.88 μs	1.07	0.04	1	5.2795	1.3123	86.25 KB	1.00

⚪ Startup / Config

Method	Mean	Error	StdDev	Min	Median	Max	Ratio	RatioSD	Rank	Gen0	Gen1	Allocated	Alloc Ratio
EggMapperStartup	1,128.804 μs	13.5841 μs	12.7066 μs	1,095.100 μs	1,130.245 μs	1,151.025 μs	1.000	0.02	3	5.8594	1.9531	95.68 KB	1.00
AutoMapperStartup	242.537 μs	0.5804 μs	0.5146 μs	241.782 μs	242.531 μs	243.358 μs	0.215	0.00	2	5.8594	-	103.64 KB	1.08
MapsterStartup	2.490 μs	0.0450 μs	0.0631 μs	2.434 μs	2.471 μs	2.648 μs	0.002	0.00	1	0.7019	0.0267	11.51 KB	0.12

⚪ Cold Start (Config + First Map per Type Pair)

Method	Mean	Error	StdDev	Min	Median	Max	Ratio	RatioSD	Rank	Gen0	Gen1	Allocated	Alloc Ratio
EggMapper	1.102 ms	0.0102 ms	0.0090 ms	1.090 ms	1.102 ms	1.118 ms	1.00	0.01	1	5.8594	3.9063	96.69 KB	1.00
AutoMapper	3.386 ms	0.0066 ms	0.0052 ms	3.379 ms	3.386 ms	3.398 ms	3.07	0.02	3	15.6250	7.8125	310.38 KB	3.21
Mapster	2.585 ms	0.0145 ms	0.0128 ms	2.568 ms	2.586 ms	2.605 ms	2.35	0.02	2	39.0625	15.6250	757.48 KB	7.83

Benchmarks run automatically on every push to main with .NET 10. See workflow

Features

✅ Compiled expression tree delegates (zero runtime reflection)
✅ ForMember / MapFrom custom mappings
✅ Ignore() members
✅ ReverseMap() bidirectional mapping
✅ Nested object mapping (inlined into parent expression tree)
✅ Collection mapping (List<T>, arrays, HashSet<T>, etc.)
✅ Flattening (src.Address.Street → dest.AddressStreet)
✅ Constructor mapping (auto-detects best-matching constructor for records)
✅ Profile-based configuration
✅ Assembly scanning
✅ Before/After map hooks
✅ Conditional mapping
✅ Null substitution
✅ Null source collection → empty destination collection (default AllowNullCollections = false semantics)
✅ Unmatched destination collection properties auto-initialized to empty (top-level + nested inline maps)
✅ Ignore() on getter-only and non-public-setter properties; non-Ignore() ops throw at config time
✅ Custom IEnumerable wrappers (e.g. SelectList) auto-constructed via cached interface-ctor lookup
✅ MaxDepth for self-referencing types
✅ Inheritance mapping
✅ Enum mapping (int ↔ enum and string ↔ enum auto-conversion)
✅ ForPath for nested destination properties
✅ .NET Dependency Injection integration (transient IMapper, scoped service support)
✅ EF Core proxy / derived type resolution (base-type + interface walk)
✅ Constructor-based type conversion in MapFrom(s => s) patterns
✅ Configuration validation
✅ CreateMap(Type, Type) runtime type mapping
✅ ITypeConverter<S,D> / ConvertUsing custom converters
✅ ShouldMapProperty global property filter
✅ Patch / partial mapping via mapper.Patch<S,D>(src, dest)
✅ Inline validation rules via .Validate() (collects all failures before throwing)
✅ IQueryable projection via ProjectTo<S,D>(config) for EF Core / LINQ providers

Mapping Tiers

EggMapper supports three complementary mapping approaches. Choose based on your use case:

	Runtime (`EggMapper`)	Attribute Mapper (`EggMapper.Generator`)	Class Mapper (`EggMapper.ClassMapper`)
API	`MapperConfiguration` + `CreateMap`	`[MapTo(typeof(Dest))]` attribute	`[EggMapper]` partial class
Mapping errors detected	Runtime	✅ Build time	✅ Build time
Reflection at map time	None (expression trees)	✅ None (generated code)	✅ None (generated code)
Startup cost	Compilation (once)	✅ None	✅ None
Custom logic	Full (`ForMember`, hooks, etc.)	`AfterMap` hook	Full custom methods
Reverse mapping	`ReverseMap()`	Separate `[MapTo]` annotation	Declare both `partial` methods
DI-friendly instance	`IMapper`	N/A (extension methods)	✅ `Instance` + constructors
Migration from AutoMapper	✅ Drop-in	Via EGG1003 suggestion	New API
Best for	Complex/conditional mapping	Simple 1:1 copies	Custom logic + compile safety

See Migration Guide to move from runtime to compile-time APIs.

Documentation

Page	Description
Getting Started	Installation and your first runtime mapping
Attribute Mapper	Compile-time extension methods with `[MapTo]`
Class Mapper	Compile-time partial mapper classes with `[EggMapper]`
Migration Guide	Moving from AutoMapper or runtime to compile-time APIs
Configuration	`MapperConfiguration` options
Profiles	Organising maps with `Profile`
Dependency Injection	ASP.NET Core / DI integration
Advanced Features	`ForMember`, conditions, hooks, etc.
Performance	Benchmark methodology & tips
API Reference	Full public API surface
Diagnostic Reference	All EGG diagnostic codes explained

Sponsor

EggMapper is built and maintained by Eggspot. If this library saves you time or money, consider supporting its development:

Sponsorships help fund:

Continuous performance optimization and benchmarking
New feature development
Bug fixes and maintenance
Documentation and community support

Contributing

We welcome contributions from the community! Here's how you can help:

Report bugs — Open an issue
Request features — Start a discussion
Submit code — Fork, branch, and open a pull request
Improve docs — Edit files in the docs/ folder (published to eggspot.github.io/EggMapper)
Share benchmarks — Run on your hardware and share results

Development Setup

git clone https://github.com/eggspot/EggMapper.git
cd EggMapper
dotnet build --configuration Release
dotnet test --configuration Release

Contribution Guidelines

Fork the repository and create a branch from main
Write tests for any new functionality
Run all tests — dotnet test --configuration Release must pass on all TFMs
Run benchmarks if changing core mapping code — cd src/EggMapper.Benchmarks && dotnet run -c Release -f net10.0 -- --filter *
Open a PR with a clear description of the change

All contributors are recognized in the GitHub Release notes automatically.

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.claude		.claude
.cursor		.cursor
.github		.github
assets		assets
docs		docs
scripts		scripts
src		src
.editorconfig		.editorconfig
.gitignore		.gitignore
CLAUDE.md		CLAUDE.md
Directory.Build.props		Directory.Build.props
EggMapper.slnx		EggMapper.slnx
LICENSE		LICENSE
README.md		README.md
llms-full.txt		llms-full.txt
llms.txt		llms.txt

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🥚 EggMapper

Overview

Migrating from AutoMapper?

Why EggMapper?

Installation

Quick Start

With Profiles

Dependency Injection

Performance

🔵 Flat Mapping (10 properties)

🟡 Flattening

🟣 Deep Mapping (2 nested objects)

🟢 Complex Mapping (nested + collection)

🟠 Collection (100 items)

🔴 Deep Collection (100 items, nested)

⚫ Large Collection (1,000 items)

⚪ Startup / Config

⚪ Cold Start (Config + First Map per Type Pair)

Features

Mapping Tiers

Documentation

Sponsor

Contributing

Development Setup

Contribution Guidelines

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