Metalama is an open-source patterns & architecture toolkit for C#.

Define your team's patterns once: the compiler writes the repetitive parts at build time and enforces your rules as you type.

Tip

Using an AI coding assistant or agent? Install Metalama.AI.Skills so it generates correct aspects, fabrics, and architecture rules from the real API instead of inferring it from training data.

Why Metalama?

• Write the pattern once, apply it everywhere: Aspects generate the repetitive code at compile time; the boilerplate never lands in the repo, so it never needs review or maintenance.
• Enforce architecture as you type: Dependency rules, naming conventions, and pattern guidelines in plain C#, with real-time IDE feedback long before the pull request.
• Stay consistent in the AI era: Hand-written or AI-generated, every line is checked against your rules; a pattern change is one file edit and the whole codebase follows at the next build.

Built on Roslyn by the PostSharp team, who have been doing compiler-level meta-programming in .NET since 2004.

When to use it?

Metalama is ideal for:

• Large projects: Automate repetitive patterns across dozens of entities and hundreds of properties or methods.
• Large teams: Align developers on consistent patterns and practices.
• Long lifecycle projects: Maintain quality over years of development.

Its main use cases are:

• Design Patterns: Singleton, Memento, Factory, Builder, Decorator, Proxy, ...
• UI Patterns: INotifyPropertyChanged, Change Tracking, Memoization, Undo/Redo, Command, Dependency Properties, ...
• Object Services: Cloning, ToString, Comparison, ...
• Defensive Programming: Code Contracts (preconditions, post-conditions, invariants)
• DevOps: Logging & Tracing, Metrics, Caching, Exception Handling
• Architecture Validation 💎
• Refactoring
• In general, Clean Code and SOLID & DRY Principles

License

Metalama is vendor-led open source: built and maintained by full-time engineers, funded by commercial licenses.

The core framework, which is the large majority of the codebase, is released under the MIT license. It cannot be taken away, relicensed, or paywalled.

Some optional extensions and IDE tooling are released under a proprietary license and are marked with a diamond 💎 symbol.

Features

• Code Generation
• Code Validation
• Immediate Editor Feedback
• Code Fix Toolkit 💎
• Ready-to-Use Aspect Libraries
• Visual Studio Tooling 💎
• Test Frameworks
• Debugging of Transformed Code
• Roslyn Extensibility SDK
• Code Query API

Resources

• Metalama Website
• Documentation
• Annotated Examples
• Release Notes
• Builds
• Metalama Tools for Visual Studio Extension

Quick Start

1. Add the Metalama.Framework package to your project:

   dotnet add package Metalama.Framework

2. Optionally, install Metalama Tools for Visual Studio Extension. It's free for individuals, non-commercial uses, and companies with up to 3 users.

3. Explore the Metalama Marketplace for ready-made aspects or examples.

4. Follow the Getting Started guide to create your first aspect.

Contributing

Contributions are accepted through the following channels:

• Share your aspects on the Metalama Marketplace.
• Contribute aspects to Metalama.Community.
• Improve the documentation. Learn how.
• Fix bugs or contribute code. Learn how.

For more details, see Contributing to Metalama.

Support

• Report issues on GitHub. Follow these recommendations.
• Ask questions and submit proposals in GitHub discussions.
• Enterprise support is available. Learn more about premium support. 💎

Packages

Below is a list of packages originating from this repository:

Package Name	Description
Metalama.Framework	This is the public API of the Metalama Framework. It incorporates a reference to Metalama.Compiler, effectively replacing the Roslyn compiler with our custom version.
Metalama.Testing.UnitTesting	Provides base classes and utilities for unit testing compile-time code.
Metalama.Testing.AspectTesting	A framework based on xUnit for testing code generation by aspects.
Metalama.Framework.Redist	Similar to Metalama.Framework, but excludes the dependency on Metalama.Compiler.
Metalama.Framework.Sdk	Facilitates the use of the Roslyn API from aspects.
Metalama.Framework.Engine	This is the core implementation of Metalama.Framework. Direct referencing of this package is discouraged and unsupported. It's intended to be a dependency for Metalama.Testing.AspectTesting.
Metalama.Framework.CompileTimeContracts	Defines the public API between compiled T# templates and Metalama.Framework.Engine.
Metalama.Framework.Introspection	Provides an API to inspect the object model that represents the compilation process of Metalama.Framework, such as aspect and advice instances, as well as its results.
Metalama.Framework.Workspaces	A supplementary API to Metalama.Framework.Introspection, designed to facilitate the loading of Visual Studio projects and solutions. This package is also useful to inspect projects that don't use Metalama. It is used by Metalama.LinqPad.
Metalama.Tool	The metalama tool for the .NET CLI.
Metalama.Extensions.DependencyInjection	A framework that allows aspects to consume dependencies from an arbitrary dependency injection framework.
Metalama.Extensions.Metrics	Implements code metrics that can be consumed by aspects and fabrics.
Metalama.Extensions.Multicast	Reproduces PostSharp attribute multicasting in Metalama, for teams porting business code from one to the other.
Metalama.Extensions.Architecture	Allows you to validate the source code against architecture rules.
Metalama.Patterns.Caching	Caching framework for Metalama.
Metalama.Patterns.Caching.Aspects	Aspects designed for Metalama caching, building upon Metalama.Patterns.Caching.
Metalama.Patterns.Caching.Backend	Provides an abstraction over caching backends, including an in-memory caching implementation.
Metalama.Patterns.Contracts	Code contract aspects like [NotNull], [Url] for contract-based programming.
Metalama.Patterns.Immutability	Represents the concept of Immutable Type so that it can be used by other packages like Metalama.Patterns.Observability.
Metalama.Patterns.Memoization	Implements a memoization aspect, i.e., simple, low-overhead caching.
Metalama.Patterns.Observability	A Metalama aspect implementing INotifyPropertyChanged.
Metalama.Patterns.Wpf	Aspects that implement WPF dependency properties and commands.
Metalama.LinqPad	Provides integration with LINQPad for inspecting projects and solutions.
Flashtrace	A structured tracing library used by Metalama.Patterns.Caching.
Flashtrace.Formatters	Object formatters used in caching and logging.

Related Repositories

Repository	License	Description
Metalama.Compiler	MIT	A Roslyn fork for source code transformations.
PostSharp.Engineering	MIT	A custom multi-repo build and CI framework.
Metalama.Community	MIT	Community-contributed aspects repository.
Metalama.Documentation	MIT	Source for documentation hosted on Metalama Docs.
Metalama.Samples	MIT	Illustrative samples available at Metalama Examples.
Metalama.Premium 💎	Proprietary	Extensions available to customers with a commercial license.

Dependencies

Direct and indirect dependencies, as well as their licensing, are documented in Third Party Notices.