NexusWindows

NexusWindows

Your Windows desktop, driven in the background.

Windows computer use for AI agents: your desktop apps observed through UI Automation and driven without taking your mouse, keyboard or foreground, with every action read back. For Claude, Codex and Antigravity.

🌐 Website · 📦 Get it with NexusSystem · ▶️ Watch the video · 📝 Changelog

▶ Click to watch the video · more on julienpiron.fr

One engine, three profiles

Claude Claude Code and Claude Desktop Page · Video · README

Codex the OpenAI Codex desktop app Page · Video · README

Antigravity Google Antigravity Page · Video · README

✨ Why NexusWindows

🫥 Background first Win32 messages and UI Automation act without activating the window: your mouse, keyboard and foreground stay yours. 🔎 Every effect read back Value, state, window: an input that cannot be verified is never counted as a success. ✋ Your yes for outward actions Send, pay, publish, delete are held until you explicitly confirm.

🖱️ Real mouse only if you allow it A last resort, used only with permission and stopped as soon as you take control back. ⚡ One native program Self-contained C# (.NET 10), x64 and ARM64: no Python, Node.js or .NET runtime to install. 🤝 Three AI apps, one engine Claude, Codex and Antigravity share the same engine and safety policy.

🚀 Quick start

Windows 10 or 11, x64 or ARM64; nothing else to install (one self-contained native program, no Python, Node.js or .NET runtime needed).

[!TIP]

Let your AI install it. NexusSystem detects your AI apps and sets up the right profile:

`text

Install Nexus for me by following https://raw.githubusercontent.com/pironjulien/NexusSystem/main/INSTALL-AI.md

`

Or the NexusSystem app from the Microsoft Store (winget install --id 9NSH2P3QLWT1 --source msstore).

Manual install (verified)

By hand, from the release files (no administrator rights):

$r = 'https://github.com/pironjulien/NexusWindows/releases/latest/download'

Invoke-WebRequest "$r/get.ps1" -OutFile get.ps1 Invoke-WebRequest "$r/SHA256SUMS.txt" -OutFile SHA256SUMS.txt (Get-FileHash get.ps1 -Algorithm SHA256).Hash # must equal the get.ps1 line of SHA256SUMS.txt gh attestation verify get.ps1 --repo pironjulien/NexusWindows --signer-repo pironjulien/NexusSystem # optional: provenance powershell -NoProfile -ExecutionPolicy Bypass -File .\get.ps1

get.ps1 downloads NexusWindows-win-x64.zip or NexusWindows-win-arm64.zip from the latest release, checks its SHA-256 against SHA256SUMS.txt, installs the engine under %USERPROFILE%\.nexus\nexus-windows and declares it to Claude Code, Claude Desktop, Codex and Antigravity when they are present. Every client starts the same stable path, %USERPROFILE%\.nexus\nexus-windows\NexusWindows.exe --mcp --agent ; updates never change it. Release files carry a build provenance attestation (gh attestation verify --repo pironjulien/NexusWindows --signer-repo pironjulien/NexusSystem). The Claude Desktop extension is nexus-windows-claude.mcpb in each release.

Updates and runtime receipts

For unattended maintenance of an existing installation, NexusSystem calls get.ps1 -UpdateOnly: it updates only the installed engine and stable launcher, without registering or enabling clients. -RefreshExistingProfiles additionally refreshes the shipped files of an already installed, active Antigravity plugin. Disabled or custom declarations and client configuration remain unchanged. Running sessions keep their engine; new connections use the new version. The launcher itself never downloads updates.

Each MCP session writes an atomic runtime receipt under %USERPROFILE%\.nexus\status\runtime, with its actual PID, process birth, loaded executable, assembly SHA-256, version and idle/busy/stopped lifecycle. MCP initialization and discovery expose the same identity. A receipt must be checked against the live process and its AI host before it can establish that a particular AI uses the installed version; an installation manifest alone cannot prove this.

⚙️ How it works

flowchart LR

A["Claude / Codex / Antigravity"] -- "stdio (MCP)" --> W["NexusWindows.exe --mcp --agent ..."] W -- "UI Automation, Win32" --> D["Windows apps (in the background)"]

One repository, one common engine, three profiles:

For current MCP requests, native file dialogs, UTF-8 stdio and blank Chromium pages, use the shared MCP cookbook. How the engine compares with Cua Driver on the same bench is in the 3 November 2026 benchmark.

[!IMPORTANT]

Outward actions (send, pay, publish, delete) are held for your explicit yes, and text read on screen is treated as

data, never as instructions.

Repository layout

• codex/native/: the common C# (.NET 10) engine, NexusWindows.exe, serving the three profiles as MCP stdio servers (--mcp --agent claude|codex|antigravity) and declaring itself to them (--register).
• commun/: the shared safety policy (garde-fous.json), the stable launcher (launcher/), the workstation installer of the immutable engine (native-runtime.ps1) and the release packaging (package.ps1).
• plugin/: the single plugin of the three AI apps (Claude Code, Codex, Antigravity), served by the native engine.
• claude/, agy/, codex/: each profile's documentation (and the Claude Desktop extension in claude/).
• tests/: xUnit tests of the engine, the launcher and the installers.

🛠️ Development

./test.ps1    # dotnet test (xUnit) of the engine, launcher and installers; offline, same command as the CI

./test.ps1 -Full # the same, plus the live tests: real Explorer launch, shared foreground token, capture session

Before a stable promotion (see NexusSystem's RELEASING.md), ./test.ps1 -Full must pass on a real interactive Windows session with a GPU, at a moment nobody is using the PC (the live tests take the shared foreground token and open real windows). The hosted CI skips those tests, so a green CI alone is not enough to promote. Releases ship the engine compiled ahead of time (Native AOT, commun/package.ps1): run the suite against that very binary, installed by get.ps1 from a local package in a throwaway profile:

./commun/package.ps1 -Version X.Y.Z -Out <dist> -Runtimes win-x64 -NoMcpb

$env:NEXUS_WINDOWS_PROFILE = ' '; $env:NEXUS_WINDOWS_SOURCE = ' \NexusWindows-win-x64.zip' powershell -NoProfile -ExecutionPolicy Bypass -File ./get.ps1 ./test.ps1 -Full -Engine ' \.nexus\nexus-windows\native\ \NexusWindows.exe'

-Engine runs the process tests (MCP over stdio, helper children) against that executable. The installers accept both engine layouts:

• Native AOT single file (releases since 3.17.0): NexusWindows.exe alone holds the code;
• framework-dependent (the working-folder installation, commun/native-runtime.ps1, and releases up to 3.16.28): NexusWindows.exe with NexusWindows.dll, .deps.json and .runtimeconfig.json, all three recorded together; a partial set is refused.

These cases live in LauncherTests, NativeRuntimeInstallerTests and PublicMaintenanceTests (get.ps1, commun/native-runtime.ps1, the stable launcher); NexusSystem's WindowsRuntime/RuntimeObservation follow the same rule since NexusSystem 1.7.0.

Build and test outputs go to %USERPROFILE%\.nexus\build\nexuswindows. The three profiles were separate repositories until 30 October 2026; those repositories have since been removed (see CHANGELOG.md).

🔐 Privacy & security

Everything runs on your PC. Nothing is sent anywhere by NexusWindows; screenshots, logs and routines stay under %USERPROFILE%\.nexus. See SECURITY.md to report a vulnerability.

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Part of the Nexus ecosystem

Your AIs (Claude, Codex, Antigravity) at work on your Windows apps, real Chrome and Android phone — in the background.

NexusSystem <img src