sagefs.nvim

sagefs.nvim is a Neovim frontend for the SageFs live F# development server. SageFs runs as a daemon and provides sub-second hot reload, live unit testing, code coverage, and a rich MCP (Model Context Protocol) surface that agents can interact with. The Neovim plugin connects to the running SageFs daemon and exposes interactive capabilities such as evaluating code cells, managing sessions, monitoring test results, and viewing live SSE updates directly in the editor. The MCP surface includes tools like get_fsi_status during warmup and send_fsharp_code once the session is ready, enabling AI agents or external tools to inspect and manipulate the live project state within SageFs.

To use the MCP tools from within Neovim, ensure SageFs is running and the sagefs.nvim MCP server is connected. You can then perform actions such as evaluating F# code in the editor, running tests, inspecting session context, and accessing live diagnostics and coverage information via the plugin’s UI and the MCP-dispatched events. The integration is designed to be transparent to your workflow: you edit, SageFs hot-reloads, tests run, and results stream back to Neovim in near real-time, with signs, panels, and SSE events keeping you informed.

Prerequisites

• A working Neovim installation (nvim --version should be recent enough for Lua support)
• A running SageFs daemon (the .NET global tool) configured for your project: sagefs --proj YourApp.fsproj
• An MCP-capable environment for the sagefs.nvim plugin (Node.js is assumed for this MCP server wrapper)

Install steps

1. Install SageFs and start the daemon for your project. Example:

   • dotnet tool install -g SageFs (if applicable)
   • sagefs --proj path/to/YourApp.fsproj
   • Ensure the SageFs API is reachable (default http://localhost:PORT if you customize it)

2. Install the sagefs.nvim Neovim plugin using your preferred plugin manager. Example with packer: -- In your plugins.lua use { 'WillEhrendreich/sagefs.nvim', config = function() require('sagefs').setup({}) end }

3. Configure the MCP server mapping (example snippet for your init): -- Lua configuration (adjust path and endpoint as needed) local mcp = { mcp_config = { mcpServers = { ["sagefs.nvim"] = { command = "node", args = {"path/to/sagefs.nvim/mcp_server.js"}, env = { SAGEFS_API_URL = "http://localhost:5000", SAGEFS_AUTH_TOKEN = "<token-in-use>" } } } } }

4. Start Neovim and ensure the MCP connection initializes. Check Neovim messages for successful MCP server handshakes and start using the plugin’s commands to evaluate code, manage sessions, and view live updates.

Tips and notes:

• The MCP surface exposed by SageFs includes tools like get_fsi_status during warmup and send_fsharp_code once ready. Agents can use these to inspect session state, type-check code, and execute F# in the live environment.
• Live SSE updates are used to stream events such as evaluation results, diagnostics, and coverage data. Ensure SSE support is not blocked by corporate proxies or firewall rules.
• For best results, keep SageFs and the sagefs.nvim plugin updated to align with the latest MCP capabilities and event formats.
• If you encounter connection issues, verify the API URL and authentication token (if used), and confirm that the SageFs daemon is listening on the expected port. Logs from SageFs and Neovim will help identify where the handshake fails.
• Environment variables can be used to customize remote endpoints, authentication, or feature flags as needed by your development environment.