SageFs FAQs

Question 1

What is SageFs and what problem does it solve?

Accepted Answer

SageFs is a live F# development server that eliminates the tedious edit-build-run cycle. It fixes the painful feedback loop of F# development by providing instant hot reloads, live unit testing, and full project context, allowing developers to see changes instantly without restarts or rebuilds.

Question 2

How does SageFs achieve sub-second hot reload?

Accepted Answer

SageFs uses Harmony patching to update method pointers at runtime. This avoids the need for full builds and restarts, applying changes to your running F# application in approximately 100ms, with browsers auto-refreshing via SSE.

Question 3

What are the key benefits of SageFs's Live Unit Testing?

Accepted Answer

SageFs offers real-time pass/fail markers and code coverage in your editor (VS Code, Neovim, etc.) for all major .NET test frameworks. Tests run automatically on edits (often under 500ms) without IL instrumentation, providing faster and more integrated feedback than traditional solutions.

Question 4

Can SageFs be used with AI development tools?

Accepted Answer

Yes, SageFs includes an MCP (Model Context Protocol) server. This allows AI agents like Copilot or Claude to interact directly with your live project environment to compile, run, type-check F# code, and execute tests.

Question 5

Which development environments and editors does SageFs support?

Accepted Answer

SageFs supports multi-frontend connections to a single daemon, including VS Code, Neovim, TUI (terminal user interface), a GPU-rendered GUI, and a web dashboard. It loads your full F# project context into the REPL, including NuGet packages and references, automatically.

SageFs

SageFs

Key Features

Use Cases

Key Features

Use Cases