---

title: FlexSim MCP Server emoji: ⚙️ colorFrom: blue colorTo: green sdk: gradio sdk_version: "5.0.0" app_file: app.py pinned: false

FlexSim MCP Server (incl. FlexSimPy)

Control and automate FlexSim simulations via the Model Context Protocol (MCP). This repository exposes a FastMCP server that launches FlexSim (via FlexSimPy) and provides tools to open models, run/stop, step, query/set node values, evaluate FlexScript, export results, and more.

Why this matters

• Bridges digital twins and AI assistants (Claude/Cursor) for manufacturing/warehouse analysis and “what-if” studies.
• Demonstrates robust systems engineering: GUI process orchestration, async I/O, protocol handling, Windows quirks, and reproducible automation.

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Design

┌─────────────────────┐       JSON-RPC        ┌─────────────────────┐
│    MCP Client       │◄────────────────────► │    MCP Server       │
│  (Claude/Cursor)    │     stdin/stdout      │  (flexsim_mcp.py)   │
└─────────────────────┘                       └──────────┬──────────┘
                                                         │
                                                         │ Python API
                                                         ▼
                                              ┌─────────────────────┐
                                              │     FlexSimPy       │
                                              │   (Python SDK)      │
                                              └──────────┬──────────┘
                                                         │
                                                         │ COM/IPC
                                                         ▼
                                              ┌─────────────────────┐
                                              │      FlexSim        │
                                              │  (Simulation Engine)│
                                              └─────────────────────┘

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Features

• MCP server entry point: mcp_server/flexsim_mcp.py
• Tools exposed:
  • Simulation control: flexsim_open_model, flexsim_reset, flexsim_run, flexsim_run_to_time, flexsim_stop, flexsim_step, flexsim_get_time
  • Model/script: flexsim_evaluate, flexsim_compile, flexsim_save_model, flexsim_new_model
  • Node access: flexsim_get_node_value, flexsim_set_node_value
  • Results/stats: flexsim_get_statistics, flexsim_export_results
• Logging: mcp_server/flexsim_mcp.log
• Reproducible environment: uv sync
• FlexSimPy build automation: utility/build_automation.py
• Integration tests: tests/integration/test_mcp_client.py (stdio-based MCP client)
• GUI sanity test: utility/integration_test.py
• Configurable behavior via config.toml and environment overrides

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Requirements

• OS: Windows
• Python: 3.12 (default; configurable via config.toml or FLEXSIM_PYTHON_VERSION)
• Package manager: uv (https://astral.sh)
• FlexSim:
  • Real runs require a local FlexSim installation (or repo-local mirror in FlexSimDev/program)
  • FlexSimPy SDK submodule is provided at depends/FlexSimPy (see .gitmodules)

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Quickstart

Guided setup (recommended)

# From the repo root
python setup_mcp_server.py

# The setup helper will:
# - Summarize your configuration (install locations, Python version, submodule presence)
# - Ensure `uv` is installed and run `uv sync`
# - Build/install FlexSimPy via `utility/build_automation.py`
# - Optionally run a GUI integration sanity test
# - Print next steps to run the MCP server and tests

Manual setup

# 1) Install dependencies
uv sync

# 2) Check (and optionally build) FlexSimPy
uv run python utility/build_automation.py --status
# To force a build with a specific Python version:
# uv run python utility/build_automation.py --python-version 3.12

# 3) Launch MCP server in test mode (keeps the process alive; launches FlexSim on first tool call)
uv run mcp_server/flexsim_mcp.py --test-mode

# 4) Run integration tests (spawns the server as a subprocess; stdio MCP client)
uv run python tests/integration/test_mcp_client.py

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Configuration

Primary configuration lives in config.toml (repo root). You can also override at runtime using environment variables.

Example (excerpt from config.toml):

[flexsim]
install_path = "FlexSimDev/program"
src_path = "C:\\Program Files\\FlexSim 2025 Update 2"

[python]
version = "3.12"

[server]
name = "FlexSimPy MCP Server"
version = "0.1.0"
http_endpoint = "http://127.0.0.1:8088/mcp"

[session]
reuse_policy = "singleton"

[logging]
level = "INFO"
log_file = "flexsim_mcp.log"

[build]
flexsimpy_dir = "depends/FlexSimPy"
auto_build = true
auto_install = true

Environment overrides (see utility/config.py):

• FLEXSIM_CONFIG_PATH – path to an alternate config.toml
• FLEXSIM_INSTALL_PATH – override FlexSim program path
• FLEXSIM_PYTHON_VERSION – override Python version for FlexSimPy
• FLEXSIM_LOG_LEVEL – override logging level

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Running the MCP server

Two modes:

• Test mode (interactive; no stdio protocol)

uv run mcp_server/flexsim_mcp.py --test-mode
# Keeps running; FlexSim launches on first tool call; intended for manual testing

• MCP stdio mode (default when no flags are passed)

uv run mcp_server/flexsim_mcp.py
# Expects MCP JSON-RPC messages via stdin/stdout; used by clients/tests

Client configuration (for Claude/Cursor/etc.):

{
  "mcpServers": {
    "flexsim": {
      "command": "uv",
      "args": [
        "--directory",
        "<repo-flexsim_mcp>/",
        "run",
        "mcp_server/flexsim_mcp.py"
      ]
    }
  }
}

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Example tool calls (JSON-RPC via MCP)

Open a model

{"jsonrpc":"2.0","id":1,"method":"tools/call",
 "params":{
   "name":"flexsim_open_model",
   "arguments":{"params":{
     "model_path":"C:/path/to/Model.fsm"
   }}
 }}

Run to time and read time

{"jsonrpc":"2.0","id":2,"method":"tools/call",
 "params":{"name":"flexsim_run_to_time","arguments":{"params":{"target_time":300}}}}

{"jsonrpc":"2.0","id":3,"method":"tools/call",
 "params":{"name":"flexsim_get_time"}}

Evaluate FlexScript

{"jsonrpc":"2.0","id":4,"method":"tools/call",
 "params":{"name":"flexsim_evaluate","arguments":{"params":{
   "script":"getmodeltime()"
 }}}}

Get/Set node value

{"jsonrpc":"2.0","id":5,"method":"tools/call",
 "params":{"name":"flexsim_get_node_value","arguments":{"params":{
   "node_path":"Model/Queue1/stats/input"
 }}}}

{"jsonrpc":"2.0","id":6,"method":"tools/call",
 "params":{"name":"flexsim_set_node_value","arguments":{"params":{
   "node_path":"Model/Processor1/variables/processtime",
   "value":5.0
 }}}}

More FlexScript examples and behavior: see eval-flexscript.md.

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Tests

Integration tests (stdio client; verifies tools and basic run sequence):

uv run python tests/integration/test_mcp_client.py
# Test 1: open model; Test 2: run for 20s, stop, verify time > 0

GUI sanity test (manual, interactive menu):

uv run python utility/integration_test.py
# Launches FlexSim GUI and provides simple interactive actions

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Repository structure

• mcp_server/flexsim_mcp.py — FastMCP server and FlexSimPy controller logic (entry point)
• utility/
  • config.py — configuration loader with env overrides
  • build_automation.py — FlexSimPy build/install orchestration (MSBuild resolution, .pyd install)
  • copy_flexsim.py — copies a FlexSim installation into FlexSimDev/ (uses flexsim.src_path)
  • integration_test.py — GUI-backed sanity test (suppresses CEF stderr, safe cleanup)
  • utility.py — helpers: suppress stderr, kill FlexSim processes, force exit
• tests/integration/
  • test_mcp_client.py — async stdio client that starts the server and calls tools
  • README.md — test descriptions and sample outputs
• depends/FlexSimPy — FlexSimPy SDK submodule
• FlexSimDev/program — optional repo-local mirror of FlexSim install
• config.toml, mcp_server_config.json, AGENTS.md, eval-flexscript.md

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Batch Experiment Orchestrator (Design)

A high-impact enhancement to run parameter sweeps with replications, gather metrics, and export a unified summary.csv (and manifest.json), enabling “what-if” studies at scale.

• Design document: Batch_Experiment_Orchestrator.md
• Status: design in-repo; implementation planned (not yet in flexsim_mcp.py)
• MVP tool (planned): flexsim_run_experiments with parameter list, seeds/replications, run_to_time, stats, artifact_dir

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Troubleshooting

• FlexSim not found:
  • Update flexsim.install_path in config.toml or set FLEXSIM_INSTALL_PATH
  • Optionally use utility/copy_flexsim.py to mirror an existing install into FlexSimDev/
• FlexSimPy unavailable:
  • Check status: uv run python utility/build_automation.py --status
  • Rebuild for the active Python version and ensure the .pyd is installed
• Stdio client issues:
  • Ensure you run the server without --test-mode when using stdio clients
  • Check mcp_server/flexsim_mcp.log for details
• GUI noise (CEF) or shutdown issues:
  • The utilities suppress CEF stderr and force a safe interpreter exit when needed