🥚 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: 2026-03-27 14:14 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)	16.18 ns	26.37 ns (1.6×)	29.60 ns (1.8×)	83.46 ns (5.2×)	16.35 ns (1.0×)
Flattening	20.13 ns	30.75 ns (1.5×)	49.36 ns (2.5×)	89.57 ns (4.5×)	25.17 ns (1.2×)
Deep (2 nested)	57.31 ns	68.33 ns (1.2×)	71.55 ns (1.2×)	130.89 ns (2.3×)	52.95 ns (0.9×)
Complex (nest+coll)	75.37 ns	96.50 ns (1.3×)	94.28 ns (1.2×)	157.61 ns (2.1×)	75.47 ns (1.0×)
Collection (100)	1.916 μs	1.864 μs (1.0×)	1.850 μs (1.0×)	2.510 μs (1.3×)	1.995 μs (1.0×)
Deep Coll (100)	6.277 μs	6.111 μs (1.0×)	6.482 μs (1.0×)	6.917 μs (1.1×)	5.772 μs (0.9×)
Large Coll (1000)	19.30 μs	18.85 μs (1.0×)	18.52 μs (1.0×)	22.90 μs (1.2×)	22.06 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	16.18 ns	0.167 ns	0.157 ns	15.94 ns	16.15 ns	16.48 ns	1.00	0.01	1	0.0048	80 B	1.00
EggMapper	26.37 ns	0.190 ns	0.169 ns	26.05 ns	26.38 ns	26.72 ns	1.63	0.02	2	0.0048	80 B	1.00
AutoMapper	83.46 ns	0.256 ns	0.239 ns	83.01 ns	83.47 ns	83.90 ns	5.16	0.05	4	0.0048	80 B	1.00
Mapster	29.60 ns	0.187 ns	0.166 ns	29.28 ns	29.56 ns	29.84 ns	1.83	0.02	3	0.0048	80 B	1.00
MapperlyMap	16.35 ns	0.196 ns	0.184 ns	16.10 ns	16.29 ns	16.62 ns	1.01	0.01	1	0.0048	80 B	1.00
AgileMapper	514.51 ns	1.664 ns	1.557 ns	511.60 ns	514.79 ns	516.59 ns	31.80	0.31	5	0.0200	344 B	4.30
EggMapperGenerator	15.94 ns	0.178 ns	0.167 ns	15.53 ns	15.98 ns	16.15 ns	0.99	0.01	1	0.0048	80 B	1.00
EggMapperClassMapper	16.74 ns	0.108 ns	0.090 ns	16.63 ns	16.74 ns	16.91 ns	1.03	0.01	1	0.0048	80 B	1.00

🟡 Flattening

Method	Mean	Error	StdDev	Min	Median	Max	Ratio	RatioSD	Rank	Gen0	Allocated	Alloc Ratio
Manual	20.13 ns	0.174 ns	0.154 ns	19.87 ns	20.13 ns	20.42 ns	1.00	0.01	1	0.0048	80 B	1.00
EggMap	30.75 ns	0.244 ns	0.204 ns	30.13 ns	30.78 ns	30.95 ns	1.53	0.01	3	0.0048	80 B	1.00
AutoMapper	89.57 ns	0.206 ns	0.172 ns	89.34 ns	89.60 ns	89.86 ns	4.45	0.03	5	0.0048	80 B	1.00
Mapster	49.36 ns	0.231 ns	0.205 ns	48.99 ns	49.34 ns	49.67 ns	2.45	0.02	4	0.0048	80 B	1.00
MapperlyMap	25.17 ns	0.132 ns	0.123 ns	24.97 ns	25.13 ns	25.38 ns	1.25	0.01	2	0.0062	104 B	1.30
AgileMapper	529.57 ns	1.187 ns	1.110 ns	527.31 ns	529.50 ns	531.21 ns	26.31	0.20	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	57.31 ns	0.494 ns	0.412 ns	56.76 ns	57.27 ns	58.15 ns	1.00	0.01	2	0.0162	272 B	1.00
EggMapper	68.33 ns	0.512 ns	0.454 ns	67.57 ns	68.38 ns	69.04 ns	1.19	0.01	3	0.0162	272 B	1.00
AutoMapper	130.89 ns	0.631 ns	0.591 ns	129.93 ns	130.87 ns	131.96 ns	2.28	0.02	5	0.0162	272 B	1.00
Mapster	71.55 ns	0.646 ns	0.604 ns	70.27 ns	71.60 ns	72.60 ns	1.25	0.01	4	0.0162	272 B	1.00
MapperlyMap	52.95 ns	0.315 ns	0.279 ns	52.35 ns	52.97 ns	53.30 ns	0.92	0.01	1	0.0162	272 B	1.00
AgileMapper	514.21 ns	1.865 ns	1.744 ns	512.00 ns	513.78 ns	517.66 ns	8.97	0.07	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	75.37 ns	0.466 ns	0.436 ns	74.75 ns	75.41 ns	76.16 ns	1.00	0.01	1	0.0191	320 B	1.00
EggMapper	96.50 ns	0.543 ns	0.481 ns	95.84 ns	96.42 ns	97.25 ns	1.28	0.01	2	0.0191	320 B	1.00
AutoMapper	157.61 ns	0.971 ns	0.908 ns	156.13 ns	157.62 ns	159.36 ns	2.09	0.02	3	0.0196	328 B	1.02
Mapster	94.28 ns	0.975 ns	0.912 ns	92.22 ns	94.66 ns	95.59 ns	1.25	0.01	2	0.0191	320 B	1.00
MapperlyMap	75.47 ns	0.740 ns	0.692 ns	74.61 ns	75.26 ns	76.41 ns	1.00	0.01	1	0.0191	320 B	1.00
AgileMapper	582.33 ns	1.241 ns	1.100 ns	580.78 ns	582.43 ns	584.49 ns	7.73	0.05	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	1.916 μs	0.0089 μs	0.0074 μs	1.901 μs	1.916 μs	1.927 μs	1.00	0.01	1	0.5283	0.0172	8.65 KB	1.00
EggMapper	1.864 μs	0.0287 μs	0.0269 μs	1.812 μs	1.868 μs	1.905 μs	0.97	0.01	1	0.5283	0.0172	8.65 KB	1.00
AutoMapper	2.510 μs	0.0425 μs	0.0398 μs	2.459 μs	2.521 μs	2.584 μs	1.31	0.02	3	0.6065	0.0191	9.95 KB	1.15
Mapster	1.850 μs	0.0358 μs	0.0335 μs	1.799 μs	1.841 μs	1.914 μs	0.97	0.02	1	0.5283	0.0172	8.65 KB	1.00
MapperlyMap	1.995 μs	0.0136 μs	0.0127 μs	1.967 μs	1.994 μs	2.019 μs	1.04	0.01	2	0.5264	0.0153	8.65 KB	1.00
AgileMapper	2.685 μs	0.0188 μs	0.0157 μs	2.661 μs	2.687 μs	2.715 μs	1.40	0.01	4	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	6.277 μs	0.0681 μs	0.0637 μs	6.168 μs	6.275 μs	6.380 μs	1.00	3	1.6708	0.0916	27.4 KB	1.00
EggMapper	6.111 μs	0.0636 μs	0.0595 μs	5.996 μs	6.122 μs	6.191 μs	0.97	3	1.6708	0.0916	27.4 KB	1.00
AutoMapper	6.917 μs	0.0447 μs	0.0396 μs	6.822 μs	6.912 μs	6.992 μs	1.10	4	1.7548	0.1068	28.7 KB	1.05
Mapster	6.482 μs	0.0742 μs	0.0694 μs	6.392 μs	6.482 μs	6.629 μs	1.03	3	1.6708	0.0916	27.4 KB	1.00
MapperlyMap	5.772 μs	0.0491 μs	0.0459 μs	5.675 μs	5.783 μs	5.854 μs	0.92	2	1.6785	0.0992	27.42 KB	1.00
AgileMapper	5.505 μs	0.0411 μs	0.0365 μs	5.468 μs	5.491 μs	5.597 μs	0.88	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	19.30 μs	0.208 μs	0.184 μs	19.06 μs	19.29 μs	19.69 μs	1.00	0.01	1	5.2490	1.3123	85.99 KB	1.00
EggMapper	18.85 μs	0.162 μs	0.135 μs	18.55 μs	18.88 μs	19.08 μs	0.98	0.01	1	5.2490	1.3123	85.99 KB	1.00
AutoMapper	22.90 μs	0.225 μs	0.211 μs	22.51 μs	22.89 μs	23.22 μs	1.19	0.02	3	5.7678	1.4343	94.34 KB	1.10
Mapster	18.52 μs	0.155 μs	0.145 μs	18.28 μs	18.49 μs	18.71 μs	0.96	0.01	1	5.2490	1.3123	85.99 KB	1.00
MapperlyMap	22.06 μs	0.172 μs	0.161 μs	21.80 μs	22.02 μs	22.38 μs	1.14	0.01	2	5.2490	1.2817	86.02 KB	1.00
AgileMapper	21.57 μs	0.266 μs	0.236 μs	21.17 μs	21.58 μs	21.97 μs	1.12	0.02	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	1,199.826 μs	6.7724 μs	6.3350 μs	1,190.649 μs	1,200.022 μs	1,210.590 μs	1.000	3	5.8594	-	95.69 KB	1.00
AutoMapperStartup	282.899 μs	1.2716 μs	1.1272 μs	280.515 μs	282.702 μs	285.338 μs	0.236	2	5.8594	-	104.04 KB	1.09
MapsterStartup	2.639 μs	0.0329 μs	0.0292 μs	2.592 μs	2.641 μs	2.695 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	1.165 ms	0.0100 ms	0.0094 ms	1.154 ms	1.165 ms	1.184 ms	1.00	0.01	1	5.8594	3.9063	95.98 KB	1.00
AutoMapper	3.297 ms	0.0157 ms	0.0139 ms	3.278 ms	3.295 ms	3.323 ms	2.83	0.02	3	15.6250	7.8125	310.17 KB	3.23
Mapster	2.552 ms	0.0129 ms	0.0114 ms	2.529 ms	2.555 ms	2.569 ms	2.19	0.02	2	39.0625	15.6250	764.06 KB	7.96

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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
• ✅ 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)	Tier 2 (EggMapper.Generator)	Tier 3 (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
Tier 2 Getting Started	Compile-time extension methods with [MapTo]
Tier 3 Getting Started	Compile-time partial mapper classes with [EggMapper]
Migration Guide	Moving from runtime to compile-time APIs
Diagnostic Reference	All EGG diagnostic codes explained
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

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 (auto-synced to the wiki)
• 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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