ILVerify

December 5, 2025 ยท View on GitHub

Intention of this project:

The goal is to create a standalone, cross platform, open-source tool that is capable of verifying MSIL code based on ECMA-335.

The main users of this tool are people working on software that emits MSIL code. These are typically compiler and profiler writers.

How to use ILVerify

ILVerify is published as a global tool package. Install it by running:

dotnet tool install --global dotnet-ilverify

Example of use:

C:\test>ilverify hello.dll -r "c:\Program Files\dotnet\shared\Microsoft.NETCore.App\2.1.12\*.dll"
All Classes and Methods in C:\test\hello.dll Verified.

Note that ILVerify requires all dependencies of assembly that is being verified to be explicitly specified on the command line.

Other tools

Historically on .NET Framework IL generators used PEVerify to make sure that they generated correct IL. PEVerify has some major limitations (e.g. it is tied to the .NET Framework, it cannot verify mscorlib.dll, etc.), which initiated this project.

Main properties of ILVerify:

  • No coupling with CoreLib: ILVerify can point to any assembly and verify it. This also includes the .NET Framework base assemblies (especially mscorlib).
  • Cross-platform, Open-Source
  • It should be easy to add new verification rules
  • Fast spin up/tear down.

The codebase

The code is split into three projects:

  • ILVerification is the library with the core verification logic,
  • ILVerification.Tests contains the tests for ILVerification,
  • ILVerify is an application that provides a command-line interface on top of ILVerification.

Tests

To test the ILVerification library we have small methods checked in as .il files testing specific verification scenarios. These tests live under src/coreclr/tools/ILVerification.Tests/ILTests. Tests are grouped into .il files based on functionalities they test. There is no strict policy here, the goal is to have a few dozen .il files instead of thousands containing each only a single method.

The test project itself is under src/coreclr/tools/ILVerification.Tests

Building and Running Tests

To run tests, you can run ./dotnet[.cmd|.sh] test src/coreclr/tools/ILVerification.Tests/ILVerification.Tests.csproj from the root of the repository.

Defining Tests

Method names in the .il files must follow the following naming convention:

Methods with Valid IL:

[FriendlyName]_Valid

The method must contain 1 '_'.

  • The part before the _ is a friendly name describing what the method does.
  • The word after the _ must be 'Valid' (Case sensitive)

E.g.: SimpleAdd_Valid

Methods with Invalid IL:

[FriendlyName]_Invalid_[ExpectedVerifierError1].[ExpectedVerifierError2]....[ExpectedVerifierErrorN]

The method name must contain 2 '_' characters.

  1. part: a friendly name
  2. part: must be the word 'Invalid' (Case sensitive)
  3. part: the expected VerifierErrors as string separated by '.'. We assert on these errors; the test fails if ILVerify does not report these errors.

E.g.: SimpleAdd_Invalid_ExpectedNumericType

Methods with special names:

In order to test methods with special names (e.g. '.ctor'), the specialname method is defined as usual and a separate empty method is added to the type:

special.[FriendlyName].[SpecialName]_[Valid | Invalid]_[ExpectedVerifierError1].[ExpectedVerifierError2]....[ExpectedVerifierErrorN]

The format of the special test method is equal to normal valid or invalid tests, except that the first part must contain 3 sub-parts separated by '.':

  1. part: the 'special' prefix
  2. part: a friendly name
  3. part: the name of the specialname method to actually test

Additionally the method signature of the special test method must be equal to the signature of the method that shall be tested.

E.g.: In order to test a specific invalid constructor method the specialname .ctor method is defined as usual, while an additional method 'special.SimpleAdd..ctor_Invalid_StackUnexpected' is defined.

The methods are automatically fed into appropriate XUnit theories based on the naming convention. Methods not following this naming conventions are ignored by the test scaffolding system.

How to contribute

All ILVerify issues are labeled with area-Tools-ILVerification. You can also look and fix TODOs in the source code.

Useful sources: