🥚 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: 2026-05-02 09:28 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)	16.22 ns	27.64 ns (1.7×)	29.80 ns (1.8×)	83.28 ns (5.2×)	16.21 ns (1.0×)
Flattening	20.10 ns	30.69 ns (1.5×)	35.27 ns (1.8×)	90.87 ns (4.5×)	25.66 ns (1.3×)
Deep (2 nested)	58.70 ns	74.35 ns (1.3×)	75.52 ns (1.3×)	108.40 ns (1.9×)	54.75 ns (0.9×)
Complex (nest+coll)	81.48 ns	104.38 ns (1.3×)	105.25 ns (1.3×)	149.23 ns (1.8×)	82.45 ns (1.0×)
Collection (100)	2.367 μs	2.353 μs (1.0×)	2.369 μs (1.0×)	2.892 μs (1.2×)	2.440 μs (1.0×)
Deep Coll (100)	6.417 μs	6.973 μs (1.1×)	7.122 μs (1.1×)	8.142 μs (1.3×)	6.730 μs (1.1×)
Large Coll (1000)	20.88 μs	23.01 μs (1.1×)	21.81 μs (1.1×)	23.54 μs (1.1×)	22.39 μs (1.1×)

* 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	Median	Min	Max	Ratio	RatioSD	Rank	Gen0	Allocated	Alloc Ratio
Manual	16.22 ns	0.394 ns	0.751 ns	15.91 ns	15.45 ns	17.78 ns	1.00	0.06	1	0.0048	80 B	1.00
EggMapper	27.64 ns	0.276 ns	0.245 ns	27.59 ns	27.26 ns	28.09 ns	1.71	0.08	2	0.0048	80 B	1.00
AutoMapper	83.28 ns	0.485 ns	0.405 ns	83.45 ns	82.24 ns	83.60 ns	5.15	0.23	4	0.0048	80 B	1.00
Mapster	29.80 ns	0.552 ns	0.516 ns	29.71 ns	28.89 ns	30.76 ns	1.84	0.09	3	0.0048	80 B	1.00
MapperlyMap	16.21 ns	0.102 ns	0.090 ns	16.18 ns	16.12 ns	16.43 ns	1.00	0.04	1	0.0048	80 B	1.00
AgileMapper	333.00 ns	1.715 ns	1.605 ns	332.86 ns	330.29 ns	336.07 ns	20.58	0.90	5	0.0205	344 B	4.30
EggMapperGenerator	16.62 ns	0.225 ns	0.210 ns	16.53 ns	16.33 ns	16.98 ns	1.03	0.05	1	0.0048	80 B	1.00
EggMapperClassMapper	16.90 ns	0.274 ns	0.256 ns	16.89 ns	16.51 ns	17.38 ns	1.04	0.05	1	0.0048	80 B	1.00

🟡 Flattening

Method	Mean	Error	StdDev	Min	Median	Max	Ratio	RatioSD	Rank	Gen0	Allocated	Alloc Ratio
Manual	20.10 ns	0.215 ns	0.190 ns	19.82 ns	20.16 ns	20.42 ns	1.00	0.01	1	0.0048	80 B	1.00
EggMap	30.69 ns	0.300 ns	0.251 ns	30.30 ns	30.73 ns	31.05 ns	1.53	0.02	3	0.0048	80 B	1.00
AutoMapper	90.87 ns	0.540 ns	0.451 ns	89.93 ns	90.94 ns	91.81 ns	4.52	0.05	5	0.0048	80 B	1.00
Mapster	35.27 ns	0.423 ns	0.396 ns	34.78 ns	35.43 ns	35.90 ns	1.76	0.02	4	0.0048	80 B	1.00
MapperlyMap	25.66 ns	0.228 ns	0.202 ns	25.35 ns	25.65 ns	26.13 ns	1.28	0.02	2	0.0062	104 B	1.30
AgileMapper	326.33 ns	2.759 ns	2.445 ns	320.09 ns	327.18 ns	328.80 ns	16.24	0.19	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	58.70 ns	0.653 ns	0.611 ns	58.00 ns	58.43 ns	59.87 ns	1.00	0.01	2	0.0162	272 B	1.00
EggMapper	74.35 ns	0.770 ns	0.721 ns	73.28 ns	74.18 ns	75.57 ns	1.27	0.02	3	0.0162	272 B	1.00
AutoMapper	108.40 ns	0.842 ns	0.787 ns	107.27 ns	108.50 ns	109.68 ns	1.85	0.02	4	0.0162	272 B	1.00
Mapster	75.52 ns	1.181 ns	0.986 ns	73.87 ns	75.39 ns	77.50 ns	1.29	0.02	3	0.0162	272 B	1.00
MapperlyMap	54.75 ns	0.608 ns	0.569 ns	54.17 ns	54.48 ns	55.89 ns	0.93	0.01	1	0.0162	272 B	1.00
AgileMapper	359.74 ns	1.816 ns	1.699 ns	357.10 ns	359.48 ns	362.36 ns	6.13	0.07	5	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	81.48 ns	1.152 ns	1.021 ns	79.77 ns	81.40 ns	83.46 ns	1.00	0.02	1	0.0191	320 B	1.00
EggMapper	104.38 ns	0.617 ns	0.515 ns	103.18 ns	104.57 ns	105.07 ns	1.28	0.02	2	0.0191	320 B	1.00
AutoMapper	149.23 ns	1.226 ns	1.024 ns	147.19 ns	149.19 ns	150.88 ns	1.83	0.03	3	0.0196	328 B	1.02
Mapster	105.25 ns	1.330 ns	1.179 ns	103.62 ns	104.95 ns	107.50 ns	1.29	0.02	2	0.0191	320 B	1.00
MapperlyMap	82.45 ns	1.168 ns	1.092 ns	81.21 ns	82.31 ns	84.63 ns	1.01	0.02	1	0.0191	320 B	1.00
AgileMapper	422.37 ns	2.801 ns	2.483 ns	418.42 ns	421.83 ns	427.95 ns	5.18	0.07	4	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	2.367 μs	0.0338 μs	0.0316 μs	2.302 μs	2.361 μs	2.425 μs	1.00	0.02	1	0.5264	0.0153	8.65 KB	1.00
EggMapper	2.353 μs	0.0293 μs	0.0274 μs	2.295 μs	2.345 μs	2.392 μs	0.99	0.02	1	0.5264	0.0153	8.65 KB	1.00
AutoMapper	2.892 μs	0.0576 μs	0.0617 μs	2.739 μs	2.900 μs	2.978 μs	1.22	0.03	2	0.6065	0.0191	9.95 KB	1.15
Mapster	2.369 μs	0.0426 μs	0.0399 μs	2.271 μs	2.371 μs	2.414 μs	1.00	0.02	1	0.5264	0.0153	8.65 KB	1.00
MapperlyMap	2.440 μs	0.0268 μs	0.0250 μs	2.395 μs	2.445 μs	2.467 μs	1.03	0.02	1	0.5264	0.0153	8.65 KB	1.00
AgileMapper	3.024 μs	0.0393 μs	0.0368 μs	2.941 μs	3.026 μs	3.085 μs	1.28	0.02	2	0.5417	0.0153	8.91 KB	1.03

🔴 Deep Collection (100 items, nested)

Method	Mean	Error	StdDev	Min	Median	Max	Ratio	RatioSD	Rank	Gen0	Gen1	Allocated	Alloc Ratio
Manual	6.417 μs	0.0689 μs	0.0575 μs	6.321 μs	6.424 μs	6.523 μs	1.00	0.01	1	1.6708	0.0916	27.4 KB	1.00
EggMapper	6.973 μs	0.0487 μs	0.0432 μs	6.905 μs	6.962 μs	7.058 μs	1.09	0.01	1	1.6708	0.0916	27.4 KB	1.00
AutoMapper	8.142 μs	0.0737 μs	0.0653 μs	8.005 μs	8.155 μs	8.239 μs	1.27	0.01	2	1.7548	0.1068	28.7 KB	1.05
Mapster	7.122 μs	0.1397 μs	0.2334 μs	6.697 μs	7.138 μs	7.751 μs	1.11	0.04	1	1.6708	0.0916	27.4 KB	1.00
MapperlyMap	6.730 μs	0.1308 μs	0.1285 μs	6.415 μs	6.738 μs	6.864 μs	1.05	0.02	1	1.6785	0.0992	27.42 KB	1.00
AgileMapper	6.345 μs	0.0600 μs	0.0561 μs	6.203 μs	6.359 μs	6.393 μs	0.99	0.01	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	20.88 μs	0.415 μs	1.042 μs	19.51 μs	20.62 μs	23.45 μs	1.00	0.07	1	5.2490	1.3123	85.99 KB	1.00
EggMapper	23.01 μs	0.449 μs	0.499 μs	22.07 μs	22.95 μs	23.63 μs	1.10	0.06	1	5.2490	1.3123	85.99 KB	1.00
AutoMapper	23.54 μs	0.458 μs	0.700 μs	22.42 μs	23.57 μs	24.99 μs	1.13	0.06	1	5.7678	1.4343	94.34 KB	1.10
Mapster	21.81 μs	0.431 μs	0.799 μs	20.03 μs	21.97 μs	23.21 μs	1.05	0.06	1	5.2490	1.3123	85.99 KB	1.00
MapperlyMap	22.39 μs	0.421 μs	0.617 μs	21.19 μs	22.47 μs	23.49 μs	1.07	0.06	1	5.2490	1.2817	86.02 KB	1.00
AgileMapper	24.65 μs	0.473 μs	0.420 μs	24.10 μs	24.56 μs	25.48 μs	1.18	0.06	1	5.2795	1.3123	86.25 KB	1.00

⚪ Startup / Config

Method	Mean	Error	StdDev	Min	Median	Max	Ratio	Rank	Gen0	Gen1	Allocated	Alloc Ratio
EggMapperStartup	1,156.911 μs	7.0329 μs	6.5785 μs	1,148.740 μs	1,154.243 μs	1,167.530 μs	1.000	3	3.9063	1.9531	95.09 KB	1.00
AutoMapperStartup	240.601 μs	1.2057 μs	1.0068 μs	239.181 μs	240.545 μs	243.021 μs	0.208	2	5.8594	-	104.15 KB	1.10
MapsterStartup	2.598 μs	0.0273 μs	0.0228 μs	2.545 μs	2.594 μs	2.638 μs	0.002	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	1.179 ms	0.0102 ms	0.0085 ms	1.165 ms	1.183 ms	1.195 ms	1.00	0.01	1	5.8594	3.9063	96.08 KB	1.00
AutoMapper	3.512 ms	0.0239 ms	0.0224 ms	3.486 ms	3.508 ms	3.553 ms	2.98	0.03	3	15.6250	7.8125	309.93 KB	3.23
Mapster	2.598 ms	0.0090 ms	0.0075 ms	2.586 ms	2.596 ms	2.610 ms	2.20	0.02	2	39.0625	15.6250	762.12 KB	7.93

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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