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Costura is an add-in for Fody

Embeds dependencies as resources.

Chat on Gitter NuGet Status

This is an add-in for Fody

It is expected that all developers using Fody become a Patron on OpenCollective. See Licensing/Patron FAQ for more information.

!!! READ THIS !!! Package is in maintenance mode !!! READ THIS !!!

In .NET Core 3 there are two new features:

With these features included in the dotnet tool set, the value proposition of Costura is greatly diminished.

Therefore we strongly recommend to try out the alternatives mentioned above.

Supported use cases

Costura will be kept in maintenance mode for the following use-cases because they are used by the maintainers:

  • C# projects (we have no experience with VB.NET, nor have any intention supporting this)
  • Library linking (e.g. embed dependencies in library projects)
  • Exe linking (e.g. embed dependencies in exe projects)
  • Windows platforms
  • Any advanced scenario that you are not willing to contribute (money, PR, etc) after discussing with the core contributes first

Non-supported use cases

  • VB.NET (see above)
  • Windows Services
  • Non-Windows platforms

Note that this list may be updated and will become more strict over time.

NuGet installation

Install the Costura.Fody NuGet package and update the Fody NuGet package:

PM> Install-Package Fody
PM> Install-Package Costura.Fody

The Install-Package Fody is required since NuGet always defaults to the oldest, and most buggy, version of any dependency.

Add to FodyWeavers.xml

Add <Costura/> to FodyWeavers.xml


How it works

Merge assemblies as embedded resources

This approach uses a combination of two methods


This Task performs the following changes

  • Take all assemblies (and pdbs) that have been marked as "Copy Local" and embed them as resources in the target assembly.
  • Injects the following code into the module initializer of the target assembly. This code will be called when the assembly is loaded into memory


static <Module>()

Configuration Options

All config options are accessed by modifying the Costura node in FodyWeavers.xml.

Default FodyWeavers.xml:

  <Costura />


This will copy embedded files to disk before loading them into memory. This is helpful for some scenarios that expected an assembly to be loaded from a physical file.

Defaults to false

<Costura CreateTemporaryAssemblies='true' />


Controls if .pdbs for reference assemblies are also embedded.

Defaults to true

<Costura IncludeDebugSymbols='false' />


Controls whether the runtimes folder, used by .NET Core, for the embedded dependencies will be embedded.

Defaults to true

<Costura IncludeRuntimeReferences='false' />


Controls whether the runtime assemblies are embedded with their full path or only with their assembly name.

For example, the reference system.text.encoding.codepages\5.0.0\runtimes\win\lib\net461\System.Text.Encoding.CodePages.dll will be embedded as costura.system.text.encoding.codepages.dll.compressed when false, so Costura will automatically load it.

It will be embedded as when true (given IncludeRuntimeReferences='true' and IncludeRuntimeAssemblies='System.Text.Encoding.CodePages'), requiring custom user code to load the embedded compressed assembly.

Defaults to false when the weaved assembly targets .NET Framework, true when the weaved assembly targets .NET Core

<Costura UseRuntimeReferencePaths='true' />


Embedded assemblies are compressed by default, and uncompressed when they are loaded. You can turn compression off with this option.

Defaults to false

<Costura DisableCompression='true' />


As part of Costura, embedded assemblies are no longer included as part of the build. This cleanup can be turned off.

Defaults to false

<Costura DisableCleanup='true' />


Costura by default will load as part of the module initialization. This flag disables that behaviour. Make sure you call CosturaUtility.Initialize() somewhere in your code.

Defaults to true

<Costura LoadAtModuleInit='false' />


Costura will by default use assemblies with a name like 'resources.dll' as a satellite resource and prepend the output path. This flag disables that behavior.

Be advised, that DLL project assembly names ending with '.resources' (resulting in *.resources.dll will lead to errors when this flag set to false.

Defaults to false

<Costura IgnoreSatelliteAssemblies='true' />

ExcludeAssemblies / ExcludeRuntimeAssemblies

A list of assembly names to exclude from the default action of "embed all Copy Local references".

Do not include .exe or .dll in the names.

Can not be defined with IncludeAssemblies.

Can use wildcards for partial assembly name matching. For example System.* will exclude all assemblies that start with System.. Wildcards may only be used at the end of an entry so for example, System.*.Private.* would not work.

Can take two forms.

As an element with items delimited by a newline.


Or as an attribute with items delimited by a pipe |.

<Costura ExcludeAssemblies='Foo|Bar' />

IncludeAssemblies / IncludeRuntimeAssemblies

A list of assembly names to include from the default action of "embed all Copy Local references".

Do not include .exe or .dll in the names.

Can not be defined with ExcludeAssemblies / IncludeRuntimeAssemblies.

Can use wildcards at the end of the name for partial matching.

Can take two forms.

As an element with items delimited by a newline.


Or as an attribute with items delimited by a pipe |.

<Costura IncludeAssemblies='Foo|Bar' />

Unmanaged32Assemblies & Unmanaged64Assemblies

Mixed-mode assemblies cannot be loaded the same way as managed assemblies.

Therefore, to help Costura identify which assemblies are mixed-mode, and in what environment to load them in you should include their names in one or both of these lists.

Do not include .exe or .dll in the names.

Can use wildcards at the end of the name for partial matching.

Can take two forms.

As an element with items delimited by a newline.


Or as a attribute with items delimited by a pipe |.

    Unmanaged64Assemblies='Foo64|Bar64' />

Native Libraries and PreloadOrder

Native libraries can be loaded by Costura automatically. To include a native library include it in your project as an Embedded Resource in a folder called costura32 or costura64 depending on the bittyness of the library.

Optionally you can also specify the order that preloaded libraries are loaded. When using temporary assemblies from disk mixed mode assemblies are also preloaded.

To specify the order of preloaded assemblies add a PreloadOrder element to the config.


Or as a attribute with items delimited by a pipe |.

<Costura PreloadOrder='Foo|Bar' />


CosturaUtility is a class that gives you access to initialize the Costura system manually in your own code. This is mainly for scenarios where the module initializer doesn't work, such as libraries and Mono.

To use, call CosturaUtility.Initialize() somewhere in your code, as early as possible.

class Program
    static Program()

    static void Main(string[] args) { ... }

Unit Testing

Most unit test frameworks need the .dlls files in order to discover and perform the unit tests. You may need to add Costura and a configuration like the below to your testing assembly.

    <Costura ExcludeAssemblies='TargetExe|TargetExeTest'


Merge from The Noun Project