M# Programming Language

Quick answer: M# (pronounced “M sharp”) is a declarative, model-driven development framework built on top of C# and .NET. You describe your application’s entities, pages and business rules in compact M# code, and the M# compiler generates the full C# data layer, database schema, and ASP.NET Core UI for you. It is used mainly for enterprise business applications where speed of delivery and consistency matter more than hand-crafted code.

M# is a niche technology, and much of what is written about it online is confused or outdated. This guide explains what M# actually is, how it relates to C#, what a typical M# project looks like with real code, where it is used, what you need to get started, its strengths and limitations compared with plain ASP.NET Core development, and whether it is worth learning as a .NET developer in 2026.

What is M# and how does it relate to C#?

M# is not a general-purpose language that competes with C#. It is a domain-specific language and code generator that sits on top of C#. Developers write M# definitions for three things: the data model (entities, properties, associations and validation), the UI (list, form and view modules bound to those entities) and business logic (rules and workflows). The M# toolchain then generates ordinary, readable C# classes, Entity Framework or ADO.NET-style data access, SQL schema scripts and ASP.NET Core pages. Anything M# cannot express, you simply write in standard C# alongside the generated code.

M# was created by Geeks Ltd, a UK software company, and is maintained with an open-source core on GitHub. One common mix-up: M# is sometimes described as “the language for Microsoft Dynamics 365 Finance and Operations”. That is incorrect. Dynamics 365 F&O customisations are written in X++, Microsoft’s own language. M# is an independent framework for building new line-of-business web applications, although it can of course integrate with Dynamics, SAP or any system that exposes an API.

How M# code is structured

An M# solution normally has four projects: Model (entity definitions), Domain (generated C# entities plus your hand-written logic), UI (module and page definitions) and Website (the generated ASP.NET Core app). You edit the first and third; the compiler produces the second and fourth. Here is what defining an entity looks like:

// Model/Entities/Customer.cs  (M# definition)
using MSharp;

namespace Domain
{
    public class Customer : EntityType
    {
        public Customer()
        {
            String("Name").Mandatory();
            String("Email").Mandatory().Accepts(TextPattern.EmailAddress).Unique();
            String("Phone");
            Date("Registered On").Mandatory().Default("c#:LocalTime.Today");
            Bool("Is Active").Mandatory().Default("true");
            Associate<City>("City").Mandatory();
            InverseAssociate<Order>("Orders", "Customer");
        }
    }
}

From these few lines M# generates a Customer C# class with typed properties, validation that enforces the mandatory and email rules, a unique index, a foreign key to City, a navigation collection for orders and the SQL to create the table. A list page for the same entity is also declarative:

// UI/Modules/Customer/CustomersList.cs  (M# definition)
using MSharp;

public class CustomersList : ListModule<Domain.Customer>
{
    public CustomersList()
    {
        HeaderText("Customers");

        Search(x => x.Name).Label("Name");
        Search(x => x.City);
        Search(x => x.IsActive);

        Column(x => x.Name);
        Column(x => x.Email);
        Column(x => x.City);
        Column(x => x.RegisteredOn);

        ButtonColumn("Edit").Icon(FA.Edit)
            .OnClick(x => x.Go<Customer.EnterPage>().Send("item", "item.ID"));

        Button("New customer").Icon(FA.Plus)
            .OnClick(x => x.Go<Customer.EnterPage>());
    }
}

Custom business logic lives in plain C# partial classes so it survives regeneration:

// Domain/Logic/Customer.cs  (hand-written C#)
namespace Domain
{
    partial class Customer
    {
        public async Task<decimal> GetLifetimeValue()
        {
            var orders = await Orders.GetList();
            return orders.Sum(o => o.Total);
        }

        protected override async Task OnValidating(EventArgs e)
        {
            await base.OnValidating(e);
            if (Phone.HasValue() && Phone.Length < 10)
                throw new ValidationException("Phone number must be at least 10 digits.");
        }
    }
}

What M# is used for

• Line-of-business web applications – CRM, inventory, HR, finance back-offices and admin portals where dozens of similar CRUD screens are needed.
• Rapid data modelling – entities, associations and validation are expressed in a few lines and stay consistent across database, API and UI.
• Integration projects – generated strongly typed entities and services make it quick to build front-ends over existing ERPs, including Dynamics 365 or SAP, through their APIs.
• Prototyping and MVPs – a working application with authentication, lists and forms can be produced in days rather than weeks.
• Standardised team output – because the generated code follows one pattern, junior and senior developers produce uniform, reviewable projects.

Requirements to start developing with M#

• Solid C# knowledge. M# definitions are C# syntax, and all custom logic is C#. Generics, lambdas, async/await and LINQ are used constantly.
• .NET SDK (current LTS) and Visual Studio or Visual Studio Code with the C# extension.
• The M# tooling – the MSharp NuGet packages, project templates and the msharp build/generation tools (there is also a Visual Studio extension with IntelliSense for M# fluent APIs).
• SQL Server (or LocalDB for development) as the default database.
• Web fundamentals – HTML, CSS and some JavaScript for customising the generated ASP.NET Core front-end.

M# vs hand-written ASP.NET Core vs low-code platforms

Popularity and who uses M#

M# does not appear in indexes such as TIOBE or the Stack Overflow survey, and its GitHub repositories have a few thousand stars across the ecosystem rather than the hundreds of thousands enjoyed by mainstream frameworks. Its users are chiefly Geeks Ltd itself, agencies and consultancies that have adopted it for client delivery, and enterprises that commissioned systems built on it and now maintain them in-house. In India, M# jobs are rare and usually appear as “.NET developer” roles at firms serving UK or European clients. Think of it as a productivity multiplier for a C# developer rather than a separate career path, in the same way that knowing a specific ORM or UI framework is.

Who should learn M#?

• .NET developers who build many back-office applications and want to stop rewriting the same list/form/validation code.
• Technical business analysts comfortable with code, because the model layer reads almost like a specification.
• System integrators building portals over ERPs and legacy databases.
• Students who already know C# and want to understand model-driven and code-generation approaches, which are also the ideas behind modern AI-assisted scaffolding tools.

If you are still choosing your first language, start with the fundamentals in From Zero to Hero: Learning Programming for Beginners, and compare the mainstream options in Top 10 Programming Languages to Learn for Career Growth. C# itself is on that list; M# is a specialisation on top of it.

Six mistakes developers make with M#

1. Editing generated files. Changes are lost on the next build. Put logic in partial classes in the Domain project.
2. Confusing M# with X++. They are unrelated; do not learn M# expecting to customise Dynamics 365 F&O.
3. Skipping C# fundamentals. M# saves typing, not understanding; async, LINQ and DI knowledge is assumed.
4. Treating it as low-code. It is a developer framework; non-programmers will struggle.
5. Fighting the conventions. M# is fastest when your UI follows its module patterns; highly bespoke front-ends are better built in plain ASP.NET Core or a JavaScript framework.
6. Ignoring generated SQL. Review the schema and add indexes for large tables; generation covers the common case, not every performance scenario.

Frequently asked questions

Is M# a Microsoft product?

No. M# is created and maintained by Geeks Ltd with an open-source core. It runs on Microsoft’s .NET platform but is not a Microsoft product and is not related to Dynamics 365’s X++ language.

Does M# code compile to C#?

Yes. The M# compiler reads your model and UI definitions and generates standard C# and ASP.NET Core code that is built and deployed exactly like any other .NET application.

Can I use M# for a public-facing website?

You can, but its sweet spot is internal business applications and portals. For marketing sites or highly designed consumer apps, the generated UI patterns are less of an advantage.

Will learning M# help me get a job in India?

Directly, rarely. Indirectly, yes: it deepens your C#, data modelling and architecture skills, and agencies serving UK clients do occasionally hire for it. List it as a specialisation under .NET, not as your headline skill.

Key takeaways

• M# is a model-driven framework and code generator built on C# and .NET, not a standalone language and not a Dynamics 365 tool.
• You declare entities, UI modules and rules; M# generates the database, data layer and ASP.NET Core pages.
• It shines for CRUD-heavy enterprise applications and prototypes, with full escape hatches to plain C#.
• Its community is small, so learn it as a productivity add-on to strong C# skills rather than a career on its own.

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