What is Microsoft's Rayfin?

Microsoft announced Rayfin at Build 2026 as a new way to build application backends on top of Microsoft Fabric.

The short version: Rayfin is an open-source SDK and CLI for defining an application backend in code.

Instead of manually wiring together a database, authentication, APIs, storage, hosting, and access policies, Rayfin aims to make those backend pieces part of the application definition. This is especially interesting in the AI coding era. Coding agents can generate frontend applications quickly, but production backends still need security, governance, data access, and deployment decisions.

Rayfin is Microsoft's attempt to make that backend layer more code-first and more suitable for both developers and coding agents. Rayfin runs on Microsoft Fabric. And Microsoft Fabric is Microsoft's unified data and analytics platform. It brings together data engineering, data warehousing, real-time analytics, data science, Power BI, OneLake, and governance into one platform.

The important point for Rayfin is this: application data can live inside the same governed Fabric environment where analytics and AI workloads already run. That means a Rayfin application is not just an app with a separate database somewhere else. It is intended to run closer to the organization's data estate.

Microsoft describes Rayfin as a backend-as-a-service platform for the agentic era. With it, you define your data model using TypeScript decorators, and Rayfin provisions and manages the backend pieces.

Getting started begins with Node's npm:

npm create @microsoft/rayfin@latest

The generated project can then be deployed and run with the Rayfin CLI:

npx rayfin up

The SDK is TypeScript-based. The Rayfin GitHub repository lists packages such as:

• @microsoft/create-rayfin for scaffolding projects
• @microsoft/rayfin-cli for deployment and management
• @microsoft/rayfin-core for entity decorators and schema definitions
• @microsoft/rayfin-client for client access to Rayfin services
• @microsoft/rayfin-auth for authentication utilities
• @microsoft/rayfin-storage for storage operations

A typical Rayfin project is therefore not a C# backend or an ASP.NET Core project. It is more like a TypeScript-defined backend model that Rayfin can turn into managed backend services.

The interesting part is the scope. Rayfin is not only trying to generate an API. It is trying to describe the application backend, including:

• data models
• authentication
• data APIs
• storage
• hosting
• access policies
• deployment to Fabric.

This makes the project worth watching even if you are not ready to use it yet.

For enterprise developers, the promise is not only speed. The bigger promise is that governance, security, and analytics are considered earlier, instead of being added after a prototype becomes important.

For .NET developers, Rayfin may feel slightly unfamiliar at first because the SDK is TypeScript-based. But the problem it tries to solve is very familiar: how do we move from a quick application idea to a backend that can actually run in a managed enterprise environment?

Good questions to ask when evaluating Rayfin:

• does the application data belong in Fabric?
• does the team already use Microsoft Fabric or Power BI?
• is the backend mostly data, authentication, APIs, and storage?
• does the team want coding agents to help scaffold backend code?
• what parts of the generated backend need human review?
• how mature are the templates and deployment workflow for your scenario?

Rayfin is not a replacement for every backend architecture. Traditional ASP.NET Core, Azure Functions, containers, queues, and databases are still useful tools.

But Rayfin is an interesting new option for Fabric-centered applications, especially when application data, analytics, AI, and governance need to live close together.

Happy data development!