SageFs

Overview

SageFs is a daemon-based F# development tool that provides sub-500ms feedback on code changes through live evaluation, inline results, test markers, and hot reloading. It exposes an MCP server with affordance-driven state machine tools for AI agents, enabling F# code execution, type-checking, test verification, and failure explanation. Multiple editors and AI agents can connect simultaneously to share the same live session state.

Try asking AI

After installing, here are 5 things you can ask your AI assistant:

• eval_code

  Evaluate F# code and return results

  Try:Evaluate this expression: List.map (fun x -> x * 2) [1; 2; 3]Try:Run this F# code snippet and show me the result
• run_tests

  Execute tests in the current session

  Try:Run all tests in my projectTry:Execute only failing tests and show me why they fail
• create_session

  Create a new session for a project

  Try:Create a new session for my F# project at /path/to/projectTry:Start a bare FSI session without any project
• switch_workflow

  Switch between REPL and Live workflows

  Try:Switch to live mode for hot reloadingTry:Change to REPL mode to redefine types
• get_diagnostics

  Retrieve current diagnostic information for the session

  Try:Show me all type errors in my projectTry:What compilation warnings do I have?
• get_coverage

  Get code coverage information for tests

  Try:Which lines of my code are covered by tests?Try:Show me test coverage for the entire project
• toggle_hot_reload

  Enable or disable hot reload functionality

  Try:Turn on hot reload for my web appTry:Disable hot reload mode
• get_test_results

  Retrieve test execution results and status

  Try:Show me the test results for the last runTry:What tests are currently failing?
• mark_tests_stale

  Mark all tests as stale to trigger re-execution

  Try:Mark all tests as stale so they run againTry:Force re-run of all tests in the project
• get_type_info

  Retrieve type information and definitions

  Try:Show me the definition of the Customer typeTry:What methods are available on this record?
• get_call_graph

  Generate a call graph for functions in the project

  Try:Show me the call graph for the main functionTry:Which functions call ProcessData?
• get_history

  Retrieve the execution history of the current session

  Try:Show me the last 10 code evaluationsTry:What was the result of the previous expression?

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Installation

dotnet tool install --global SageFs

{
  "mcpServers": {
    "sagefs": {
      "command": "sagefs",
      "args": ["mcp"]
    }
  }
}

FAQ

How is SageFs different from Ionide?

Ionide provides IntelliSense and diagnostics through the F# Compiler Service. SageFs adds live execution: eval expressions, see inline results, continuous test feedback, and hot reloading.

Can I use both REPL and Live modes?

Yes, SageFs supports both modes. REPL mode allows full type redefinition, while Live mode enables browser hot reload. You can switch between them as needed.

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