SimConnect MCP

SimConnect MCP Server

An MCP (Model Context Protocol) server that connects AI coding agents to Microsoft Flight Simulator via SimConnect. This server is built for add-on development — full read/write access to SimVars, L-vars, events, calculator code execution, and embedded documentation.

What It Does

• Read/write any SimVar — altitude, heading, speed, autopilot settings, engine parameters, and 1,080+ more from a comprehensive built-in catalog, with unit selection and honest failures on a rejected write
• Read/write L-vars — aircraft-specific local variables used by add-on developers (Fenix A320, FlyByWire A32NX, PMDG, etc.), including live enumeration of what the loaded aircraft has actually registered
• PMDG 777 and 737 NG3 native SDK support — direct access to all aircraft data fields and control events via the PMDG SDK Client Data Areas, plus CDU screen reading with colors/formatting
• Trigger events — toggle switches, set autopilot modes, control lights, fire custom MobiFlight events
• Execute RPN calculator code — run arbitrary Reverse Polish Notation code directly in the sim
• Search and discover variables — searchable catalogs of SimVars, events, and aircraft-specific L-vars with human-readable names and valid values
• Facilities lookup — nearby airports sorted by distance and detail lookup for a specific airport, waypoint, NDB or VOR by ICAO identifier, read directly from SimConnect's facility subscription
• Flight and scenario tools — load and save .FLT flights, load a .PLN flight plan, and spawn an AI aircraft or object, for scripting test scenarios instead of setting them up by hand
• Embedded documentation — SimConnect reference docs served as MCP resources, available offline
• Aircraft-specific catalogs — pre-built variable databases with panel groupings, display names, and value descriptions. Ships with 1,607 PMDG 777 variables (777-200LR/200F/300ER/F) and 1,861 PMDG 737 NG3 variables (-600/700/800/900 incl. BBJ/BDSF/BCF).
• HubHop integration — search the MobiFlight HubHop community preset database directly as an MCP tool, or use the built-in client to generate and extend L-var catalogs for any supported aircraft

Prerequisites

• Microsoft Flight Simulator (MSFS 2020 or 2024) running on the same machine
• [uv](https://docs.astral.sh/uv/) — provides uvx, which fetches the server and its Python runtime for you
• MobiFlight WASM Module (optional, for L-var support) — install in your MSFS Community folder. Download from MobiFlight

Installation

Published on PyPI as simconnect-mcp, and listed in the MCP Registry as io.github.robin24/simconnect-mcp.

Once uv is installed, no separate install step is needed — uvx fetches and runs the server on demand:

uvx simconnect-mcp

That starts the server on stdio, which is what an MCP client does for you. Run it by hand only to check that it starts; press Ctrl+C to stop.

To pin a version, use uvx simconnect-mcp@1.0.1.

From source (for development)

git clone https://github.com/robin24/simconnect-mcp.git

cd simconnect-mcp

Creates the virtual environment and installs the dev group too

uv sync

Configuring as an MCP Server

Claude Code

Via CLI:

claude mcp add --transport stdio simconnect -- uvx simconnect-mcp

Or to make it available across all projects:

claude mcp add --transport stdio --scope user simconnect -- uvx simconnect-mcp

Via JSON (~/.claude/settings.json or project-level .claude/settings.json):

{

"mcpServers": { "simconnect": { "command": "uvx", "args": ["simconnect-mcp"] } } }

OpenAI Codex CLI

Via CLI:

codex mcp add simconnect -- uvx simconnect-mcp

Via JSON:

{

"mcpServers": { "simconnect": { "command": "uvx", "args": ["simconnect-mcp"] } } }

Gemini CLI

Via CLI:

gemini mcp add --transport stdio simconnect -- uvx simconnect-mcp

Via JSON (~/.gemini/settings.json):

{

"mcpServers": { "simconnect": { "command": "uvx", "args": ["simconnect-mcp"] } } }

MCP Inspector (Interactive Testing)

uv run mcp dev src/simconnect_mcp/server.py

Note: To run a local checkout instead of the published package, replace

uvx simconnect-mcp with uv run --directory /path/to/simconnect-mcp simconnect-mcp,

using the absolute path to your clone.

Tools (32)

Every tool is prefixed msfs_, carries explicit readOnlyHint/destructiveHint annotations, and returns a typed result or a structured error — never a fabricated success. The tables below are generated from the live server (name, kind, and title come straight from each tool's ToolAnnotations); descriptions are the one-line summary from the tool's own docstring:

uv run python -c "

import asyncio from simconnect_mcp.server import mcp async def m(): for t in sorted(await mcp.list_tools(), key=lambda x: x.name): kind = 'read' if t.annotations.readOnlyHint else 'write' print(f'| \{t.name}\ | {kind} | {t.annotations.title} |') asyncio.run(m())"

Connection (3)

SimVar Operations (6)

Units: msfs_get_simvar (and msfs_set_simvar) accept an optional unit argument and always report the unit actually used in the result. Omit unit and the bundled SimVar catalog supplies a sensible default for that variable; for a variable the catalog doesn't know, the default is "number".

Event Operations (3)

L-Var Operations (6)

msfs_list_lvars asks the MobiFlight WASM module to enumerate what the aircraft has *actually* registered, live — but the module caps its reply at 1000 names and still reports the list as complete when it truncates. A busy add-on setup (GSX and similar) can crowd the aircraft's own variables out of the response entirely; watch for truncated: true. Treat the catalogs and the live listing as a starting point, not a guaranteed inventory — msfs_get_lvar reads any name you supply, whether or not it surfaced in either one.

Aircraft State (1)

Facilities (2)

Airports are world-wide (SimConnect returns the full 85,249-airport list, cached after the first collection). Waypoints, NDBs and VORs are scoped to wherever the aircraft currently is, so they are re-collected on every call rather than cached — a cached navaid list would keep answering for the aircraft's *previous* position after a reposition or a flight.

Utilities (2)

PMDG 777 / 737 NG3 (3)

These tools use the PMDG SDK Client Data Areas for direct binary access to the aircraft state — bypassing the MobiFlight L-var bridge. The right SDK (777 or 737 NG3) is auto-detected from the loaded aircraft, or can be forced with the variant argument. Requires EnableDataBroadcast=1 and EnableCDUBroadcast.N=1 in the aircraft's options.ini (777_Options.ini or 737NG3_Options.ini). The 777 has three CDUs (Capt/Center/F-O); the 737 NG3 has two (Capt/F-O). See PMDG 777 SDK Reference and PMDG 737 NG3 SDK Reference for details.

HubHop (2)

Unlike every other tool, these two reach HubHop's HTTP API rather than the simulator, so they work with MSFS closed. The first call downloads and caches the full preset database (~17 MB); later calls in the same server process are served from that in-memory cache, which both tools share and which re-fetches on its own every 6 hours. Either tool accepts refresh=true to force an immediate re-fetch.

Flight and Scenario (4)

| msfs_load_flight_plan | write | Load a .PLN flight plan into the aircraft's GPS/FMS, replacing whatever plan is currently activ