🥚 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.

Sponsored by eggspot.app

📖 Full documentation →

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:

1. Replace using AutoMapper; with using EggMapper;
2. 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: 2026-09-15 13:57 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)	15.36 ns	27.67 ns (1.8×)	28.51 ns (1.9×)	83.06 ns (5.4×)	15.46 ns (1.0×)
Flattening	19.06 ns	30.65 ns (1.6×)	36.62 ns (1.9×)	88.49 ns (4.6×)	22.70 ns (1.2×)
Deep (2 nested)	54.35 ns	65.44 ns (1.2×)	69.31 ns (1.3×)	121.82 ns (2.2×)	49.91 ns (0.9×)
Complex (nest+coll)	71.15 ns	93.34 ns (1.3×)	89.92 ns (1.3×)	157.63 ns (2.2×)	72.00 ns (1.0×)
Collection (100)	1.790 μs	1.710 μs (1.0×)	1.766 μs (1.0×)	2.323 μs (1.3×)	1.924 μs (1.1×)
Deep Coll (100)	5.353 μs	5.871 μs (1.1×)	5.912 μs (1.1×)	6.664 μs (1.2×)	5.504 μs (1.0×)
Large Coll (1000)	17.76 μs	17.26 μs (1.0×)	17.53 μs (1.0×)	21.49 μs (1.2×)	18.67 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	Min	Median	Max	Ratio	RatioSD	Rank	Gen0	Allocated	Alloc Ratio
Manual	15.36 ns	0.265 ns	0.221 ns	14.89 ns	15.41 ns	15.67 ns	1.00	0.02	1	0.0048	80 B	1.00
EggMapper	27.67 ns	0.495 ns	0.463 ns	27.02 ns	27.67 ns	28.61 ns	1.80	0.04	2	0.0048	80 B	1.00
AutoMapper	83.06 ns	0.676 ns	0.565 ns	82.45 ns	82.93 ns	84.58 ns	5.41	0.08	3	0.0048	80 B	1.00
Mapster	28.51 ns	0.398 ns	0.353 ns	27.86 ns	28.58 ns	29.08 ns	1.86	0.03	2	0.0048	80 B	1.00
MapperlyMap	15.46 ns	0.374 ns	0.350 ns	14.91 ns	15.55 ns	16.03 ns	1.01	0.03	1	0.0048	80 B	1.00
AgileMapper	500.13 ns	2.157 ns	2.017 ns	496.61 ns	500.12 ns	503.68 ns	32.57	0.47	4	0.0200	344 B	4.30
EggMapperGenerator	15.27 ns	0.272 ns	0.241 ns	14.95 ns	15.21 ns	15.68 ns	0.99	0.02	1	0.0048	80 B	1.00
EggMapperClassMapper	15.77 ns	0.202 ns	0.169 ns	15.52 ns	15.77 ns	16.16 ns	1.03	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	19.06 ns	0.206 ns	0.193 ns	18.77 ns	19.03 ns	19.37 ns	1.00	0.01	1	0.0048	80 B	1.00
EggMap	30.65 ns	0.592 ns	0.581 ns	29.79 ns	30.55 ns	31.81 ns	1.61	0.03	3	0.0048	80 B	1.00
AutoMapper	88.49 ns	0.391 ns	0.365 ns	87.68 ns	88.66 ns	88.94 ns	4.64	0.05	5	0.0048	80 B	1.00
Mapster	36.62 ns	0.535 ns	0.475 ns	35.99 ns	36.43 ns	37.86 ns	1.92	0.03	4	0.0048	80 B	1.00
MapperlyMap	22.70 ns	0.375 ns	0.351 ns	22.16 ns	22.66 ns	23.36 ns	1.19	0.02	2	0.0062	104 B	1.30
AgileMapper	534.62 ns	3.249 ns	2.880 ns	530.84 ns	533.85 ns	541.99 ns	28.05	0.31	6	0.0200	344 B	4.30

🟣 Deep Mapping (2 nested objects)

Method	Mean	Error	StdDev	Min	Median	Max	Ratio	RatioSD	Rank	Gen0	Allocated	Alloc Ratio
Manual	54.35 ns	0.855 ns	0.800 ns	53.02 ns	54.25 ns	56.00 ns	1.00	0.02	2	0.0162	272 B	1.00
EggMapper	65.44 ns	1.257 ns	1.345 ns	63.24 ns	65.36 ns	68.38 ns	1.20	0.03	3	0.0162	272 B	1.00
AutoMapper	121.82 ns	2.341 ns	2.695 ns	118.75 ns	120.89 ns	127.14 ns	2.24	0.06	5	0.0162	272 B	1.00
Mapster	69.31 ns	1.278 ns	1.133 ns	67.93 ns	68.97 ns	71.82 ns	1.28	0.03	4	0.0162	272 B	1.00
MapperlyMap	49.91 ns	0.745 ns	0.696 ns	48.19 ns	50.00 ns	50.85 ns	0.92	0.02	1	0.0162	272 B	1.00
AgileMapper	513.02 ns	4.132 ns	3.865 ns	506.92 ns	511.42 ns	521.35 ns	9.44	0.15	6	0.0248	424 B	1.56

🟢 Complex Mapping (nested + collection)

Method	Mean	Error	StdDev	Min	Median	Max	Ratio	RatioSD	Rank	Gen0	Allocated	Alloc Ratio
Manual	71.15 ns	1.091 ns	1.020 ns	69.81 ns	71.02 ns	73.28 ns	1.00	0.02	1	0.0191	320 B	1.00
EggMapper	93.34 ns	1.038 ns	0.867 ns	91.80 ns	93.38 ns	94.99 ns	1.31	0.02	2	0.0191	320 B	1.00
AutoMapper	157.63 ns	2.769 ns	2.590 ns	153.02 ns	158.86 ns	160.31 ns	2.22	0.05	3	0.0196	328 B	1.02
Mapster	89.92 ns	1.123 ns	1.050 ns	88.36 ns	89.78 ns	91.86 ns	1.26	0.02	2	0.0191	320 B	1.00
MapperlyMap	72.00 ns	0.747 ns	0.662 ns	71.16 ns	71.99 ns	73.24 ns	1.01	0.02	1	0.0191	320 B	1.00
AgileMapper	541.38 ns	3.835 ns	3.587 ns	533.88 ns	541.60 ns	547.47 ns	7.61	0.12	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	1.790 μs	0.0357 μs	0.0489 μs	1.727 μs	1.775 μs	1.907 μs	1.00	0.04	1	0.5283	0.0172	8.65 KB	1.00
EggMapper	1.710 μs	0.0244 μs	0.0216 μs	1.668 μs	1.714 μs	1.743 μs	0.96	0.03	1	0.5283	0.0172	8.65 KB	1.00
AutoMapper	2.323 μs	0.0292 μs	0.0228 μs	2.292 μs	2.319 μs	2.383 μs	1.30	0.04	3	0.6065	0.0191	9.95 KB	1.15
Mapster	1.766 μs	0.0346 μs	0.0518 μs	1.673 μs	1.756 μs	1.885 μs	0.99	0.04	1	0.5283	0.0172	8.65 KB	1.00
MapperlyMap	1.924 μs	0.0234 μs	0.0219 μs	1.893 μs	1.924 μs	1.961 μs	1.08	0.03	2	0.5283	0.0172	8.65 KB	1.00
AgileMapper	2.623 μs	0.0482 μs	0.0451 μs	2.539 μs	2.616 μs	2.697 μs	1.47	0.05	4	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	5.353 μs	0.0914 μs	0.0855 μs	5.213 μs	5.314 μs	5.495 μs	1.00	0.02	1	1.6708	0.0916	27.4 KB	1.00
EggMapper	5.871 μs	0.0987 μs	0.0923 μs	5.681 μs	5.891 μs	6.005 μs	1.10	0.02	2	1.6708	0.0916	27.4 KB	1.00
AutoMapper	6.664 μs	0.1311 μs	0.1287 μs	6.393 μs	6.687 μs	6.841 μs	1.25	0.03	3	1.7548	0.1068	28.7 KB	1.05
Mapster	5.912 μs	0.1066 μs	0.1185 μs	5.729 μs	5.921 μs	6.149 μs	1.10	0.03	2	1.6708	0.0916	27.4 KB	1.00
MapperlyMap	5.504 μs	0.1031 μs	0.1013 μs	5.290 μs	5.491 μs	5.681 μs	1.03	0.02	1	1.6785	0.0992	27.42 KB	1.00
AgileMapper	5.125 μs	0.1001 μs	0.0887 μs	5.011 μs	5.105 μs	5.299 μs	0.96	0.02	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	17.76 μs	0.277 μs	0.245 μs	17.45 μs	17.70 μs	18.30 μs	1.00	0.02	1	5.2490	1.3123	85.99 KB	1.00
EggMapper	17.26 μs	0.327 μs	0.321 μs	16.58 μs	17.23 μs	17.88 μs	0.97	0.02	1	5.2490	1.3123	85.99 KB	1.00
AutoMapper	21.49 μs	0.322 μs	0.285 μs	20.82 μs	21.55 μs	21.81 μs	1.21	0.02	2	5.7678	1.4343	94.34 KB	1.10
Mapster	17.53 μs	0.348 μs	0.453 μs	17.00 μs	17.41 μs	18.67 μs	0.99	0.03	1	5.2490	1.3123	85.99 KB	1.00
MapperlyMap	18.67 μs	0.324 μs	0.303 μs	18.17 μs	18.76 μs	19.17 μs	1.05	0.02	1	5.2490	1.2817	86.02 KB	1.00
AgileMapper	21.08 μs	0.401 μs	0.375 μs	20.53 μs	21.06 μs	21.65 μs	1.19	0.03	2	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	1,149.892 μs	4.5725 μs	4.0534 μs	1,141.599 μs	1,150.714 μs	1,155.339 μs	1.000	3	3.9063	1.9531	95.31 KB	1.00
AutoMapperStartup	286.999 μs	2.3138 μs	1.9321 μs	284.670 μs	286.450 μs	291.391 μs	0.250	2	5.8594	-	103.76 KB	1.09
MapsterStartup	3.173 μs	0.0617 μs	0.0606 μs	3.089 μs	3.166 μs	3.279 μs	0.003	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	1.155 ms	0.0145 ms	0.0135 ms	1.137 ms	1.153 ms	1.181 ms	1.00	0.02	1	5.8594	3.9063	96.56 KB	1.00
AutoMapper	3.271 ms	0.0276 ms	0.0258 ms	3.241 ms	3.265 ms	3.323 ms	2.83	0.04	3	15.6250	7.8125	309.93 KB	3.21
Mapster	2.494 ms	0.0149 ms	0.0140 ms	2.470 ms	2.491 ms	2.516 ms	2.16	0.03	2	46.8750	15.6250	766.77 KB	7.94

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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.

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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

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

All contributors are recognized in the GitHub Release notes automatically.

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