SageFS
Sage Mode for F# development — REPL with solution or project loading, Live Testing for FREE, Hot Reload, and session management.
What is SageFS?
SageFS is a Model Context Protocol (MCP) server that allows AI assistants like Claude, Cursor, and VS Code to sage mode for f# development — repl with solution or project loading, live testing for free, hot reload, and session management.
Sage Mode for F# development — REPL with solution or project loading, Live Testing for FREE, Hot Reload, and session management.
This server falls under the Developer Tools category on MCPgee, the world's largest MCP server directory with 33,000+ servers.
Features
- Sage Mode for F# development — REPL with solution or project
Use Cases
Maintainer
Works with
Installation
Manual Installation
npx sagefsConfiguration
Configuration Details
claude_desktop_config.json
Performance
Response Metrics
Resource Usage
How to Set Up and Use SageFS
SageFS is an MCP server and daemon for F# development that brings a persistent, hot-reloading F# Interactive (FSI) REPL to AI assistants and editors. It exposes 17 focused MCP tools covering session management, trusted code evaluation, live test execution with pass/fail feedback, coverage tracking, and hot reload with approximately 100ms patching latency. F# developers use it so their AI assistant can write, run, and iterate on F# code in real time without waiting for full compilation cycles.
Prerequisites
- .NET 10 SDK installed (required — SageFS is a .NET global tool)
- An MCP-compatible client that supports the streamable-http transport (e.g. Claude Desktop with HTTP MCP support, or a custom MCP client)
- An active REAPER project or F# solution/project file for the server to load
Install SageFS as a .NET global tool
Install SageFS from NuGet using the dotnet tool command. The .NET 10 SDK must already be installed.
dotnet tool install --global SageFsVerify the installation
Check that the sagefs command is available and the environment is valid.
sagefs --version
sagefs checkStart the SageFS daemon
Run the daemon in supervised mode for automatic restart on crash. The MCP server starts on port 37749 by default.
sagefs --supervisedConfigure your MCP client to connect
Add SageFS to your MCP client configuration using the streamable-http transport. The daemon must be running before the client connects.
{
"mcpServers": {
"sagefs": {
"type": "streamable-http",
"url": "http://localhost:37749/"
}
}
}Create a per-directory config (optional)
Add a .SageFs/config.fsx file to your project root to auto-load your solution or project when SageFS starts a session in that directory.
// .SageFs/config.fsx
{ DirectoryConfig.empty with
Load = Projects ["src/MyApp.fsproj"]
InitScript = Some "setup.fsx" }Open the dashboard
Navigate to the SageFS dashboard in a browser to view active sessions, live diagnostics, and test results.
# Dashboard URL
http://localhost:37750/dashboardSageFS Examples
Client configuration
MCP client configuration to connect to a locally running SageFS daemon using streamable-http.
{
"mcpServers": {
"sagefs": {
"type": "streamable-http",
"url": "http://localhost:37749/"
}
}
}Prompts to try
Commands you can give an AI assistant connected to SageFS to develop and test F# code interactively.
- "Create a new FSI session and load the MyApp.fsproj project."
- "Evaluate this F# expression in the active session: [1..10] |> List.map (fun x -> x * x)"
- "Run all tests in the Authentication module and show pass/fail results."
- "Hot-reload the updated Parser.fs file without restarting the session."
- "Show current test coverage for the Domain layer."Troubleshooting SageFS
sagefs command not found after installation.
The .NET global tools directory (~/.dotnet/tools on Unix, %USERPROFILE%\.dotnet\tools on Windows) must be on your PATH. Add it and restart your terminal: export PATH="$PATH:$HOME/.dotnet/tools"
MCP client cannot connect to http://localhost:37749/.
Ensure the SageFS daemon is running with 'sagefs --supervised'. Use 'sagefs status' to check. If the port is taken, start with a different port: sagefs --mcp-port 37800 and update the URL in your client config.
Type redefinition errors (FS0037) when evaluating F# code.
This occurs in Live workflow mode, which disables type redefinition for hot reload compatibility. Switch to REPL mode via the editor command palette or ':SageFsWorkflow repl' to allow type redefinition in your FSI session.
Frequently Asked Questions about SageFS
What is SageFS?
SageFS is a Model Context Protocol (MCP) server that sage mode for f# development — repl with solution or project loading, live testing for free, hot reload, and session management. It connects AI assistants to external tools and data sources through a standardized interface.
How do I install SageFS?
Follow the installation instructions on the SageFS GitHub repository. Clone the repo, install dependencies, and add the server config to your AI client.
Which AI clients work with SageFS?
SageFS works with all major MCP-compatible AI clients including Claude Desktop, Claude Code, Cursor, VS Code (GitHub Copilot), Windsurf, and Cline.
Is SageFS free to use?
Yes, SageFS is open source and available under the MIT license. You can use it freely in both personal and commercial projects.
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Set Up SageFS in Your Editor
Choose your AI client for step-by-step setup instructions.
Quick Config Preview
Add this to your claude_desktop_config.json or .cursor/mcp.json
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