NexusBrowser

NexusBrowser

Your real Chrome, driven by AI agents in background tabs.

Antigravity, Claude and Codex use your own Chrome, with your sessions and extensions, each in its own background tabs, while you keep browsing in yours.

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

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

✨ Why NexusBrowser

🌐 Your real Chrome Your sessions and extensions, not a separate headless browser or an empty profile. 🗂️ Background tabs, per agent Each agent works in its own tabs, grouped under its name, without activating them or taking your cursor. 🖱️ Trusted input Real mouse and keyboard events through the Chrome DevTools Protocol, with Playwright-style locators in every frame.

🧰 49 MCP tools Dialogs, network with response bodies, cross-origin iframes, exports (page, Google Docs/Sheets/Slides, YouTube transcript), downloads, WebMCP. 🛡️ Guard rails in the bridge Tab ownership, a DevTools allowlist, masked secrets, and your yes for every outward action (send, pay, publish). 🛑 Emergency stop One file (or Ctrl+Alt+Shift+Esc with NexusWindows) cancels running commands and refuses every action for 120 s.

Windows 10/11 (x64 and ARM64) · Chrome 116+ · self-contained .NET engine, nothing else to install · MIT licence

See it in action

Why a bridge, next to each agent's own browser tools

Browser automation usually means a separate headless browser (no sessions, no extensions) or screen-level computer use that moves the user's cursor and brings the window to the front. NexusBrowser works inside the browser the user already uses, without activating the agent's tab or window, and keeps the guard rails in the extension and the bridge rather than in the agent: tab ownership, an allowlist of DevTools commands, masked secrets, an emergency stop.

• Antigravity: its own browser agent runs in a separate Chrome profile, without the cookies or sign-ins of the user's browsing (Antigravity docs). NexusBrowser gives it the user's real Chrome.
• Claude and Codex already have their own Chrome extension (Claude in Chrome, the Codex Chrome extension). NexusBrowser complements it where a bridge with the DevTools protocol helps: JavaScript dialogs (browser_handle_dialog), detailed network capture with response bodies, elements inside cross-origin iframes, content and Google Docs/Sheets/Slides exports, and downloads.

Until 2.4.0 it was published here as "Antigravity Browser Bridge", for Antigravity only. Since 2.6.0 it is a neutral bridge shared by several agents.

🚀 Quick start

Windows 10 or 11 and Google Chrome. No admin rights, nothing else to install first.

[!TIP]

Let your AI install it. Paste this sentence into Claude Code, Codex or Antigravity:

`text

Install and set up NexusBrowser 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): it installs NexusBrowser for you. New versions are no longer published to PyPI; earlier packages stay available.

[!IMPORTANT]

One manual step: load the extension. Chrome opens chrome://extensions and the extension folder is copied to

the clipboard: turn on Developer mode (top right), click Load unpacked, paste the folder (Ctrl+V) and click

Select Folder. Outside the Chrome Web Store, Chrome installs an extension this way only. The installer waits and

says when the extension is connected.

Then restart your AI app and ask it, for example: *"Open https://example.com in a background tab and give me the page as Markdown."*

Manual install (verified)

Download the installer and the checksums of the latest release, check the installer, then run it as a file (never paste a downloaded script into PowerShell):

$r = 'https://github.com/pironjulien/NexusBrowser/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 match the get.ps1 line of SHA256SUMS.txt gh attestation verify get.ps1 --repo pironjulien/NexusBrowser --signer-repo pironjulien/NexusSystem # optional: build provenance powershell -NoProfile -ExecutionPolicy Bypass -File .\get.ps1

It downloads the latest release for your PC (x64 or ARM64), checks it against SHA256SUMS.txt, unpacks it into %LOCALAPPDATA%\NexusBrowser\app, sets up the local bridge, the native host and the shared MCP daemon (127.0.0.1:16182, shared token file NEXUS_MCP_TOKEN_FILE, otherwise ~\.nexus\mcp-token.txt, mirrored in your user variable NEXUS_MCP_TOKEN), and declares the nexus-browser server to every AI client it finds: Claude Code, Claude Desktop, Codex and Antigravity. No Python, no .NET to install: the engine is self-contained. Then load the extension as described above.

Updates and automatic maintenance

Run the installer again to update: the folder stays the same, so Chrome keeps the extension and reloads it. The new version is prepared beside the working one and checked first; a failed update restores the previous version. Chrome and the AI apps keep running. A bridge with running calls or agent-owned tabs keeps serving; the installer asks an idle bridge to exit cooperatively and never terminates it. Bridges older than 2.33.2 switch on their next natural start because they do not implement this protocol. The daemon has a separate session-preserving restart protocol from 2.33.3: older or unrecognized daemons keep serving until natural exit, and the installer writes no restart request for them.

The bridge can also update a public install itself (the contract shared by the Nexus products): it writes ~\.nexus\status\browser.json (version, latest read from the releases/latest redirect at most once a day, state, message), GET /api/update returns it and POST /api/update (bridge token) starts the "NexusBrowser Update" task, which runs get.ps1 outside the bridge and records done or failed (the current version is kept; deferred while an agent works in Chrome). A clone updates with git instead.

Automatic maintenance is owned by NexusSystem (get-nexus.ps1 -Maintain), not by a second product timer. It calls get.ps1 -UpdateOnly on an already installed release: no new AI app is configured and disabled or custom routes stay untouched. Published, installed and loaded versions are distinct; a deferred activation is retried by NexusSystem. NEXUS_UPDATE_RESULT reports completion only after the daemon and bridge match the installed build fingerprint and the loaded Chrome extension is verified. A developer checkout is never pulled or built automatically. For a Store extension, Chrome must first download the published Store update; a local reload alone cannot obtain it. Updates awaiting Store review or rollout remain deferred while the current tools keep serving.

Updating an existing installation also checks the extension's loaded version/features and reloads it when needed, then asks the shared MCP daemon to move to the new build once idle. An update defers while an agent owns browser tabs; user tabs are never driven or activated by the refresh. If Chrome is closed, it loads the updated extension files on its next launch; that state is not a live validation.

Installed an AI client later? Run the installer again too. An entry you wrote yourself, or a nexus-browser plugin that already provides the server, is never changed.

Other MCP clients: Gemini CLI, Claude Desktop extension

The installer registers Claude Code, Claude Desktop, Codex and Antigravity automatically. The former PyPI package is retired; new versions are distributed through GitHub releases and NexusSystem.

Gemini CLI: gemini extensions install https://github.com/pironjulien/NexusBrowser (the shared local daemon of the one-time install, with the token of NEXUS_MCP_TOKEN, from gemini-extension.json).

Claude Desktop extension: download nexus-browser-win-x64.mcpb (ARM64 PC: nexus-browser-win-arm64.mcpb) and drop it on Claude Desktop's window, or add it in Settings > Extensions (it carries the self-contained engine).

Without the bridge, the server still starts and lists its 49 tools, and every call answers with a clear error that points to the one-time install.

⚙️ How it works

flowchart LR

A["Claude / Codex / Antigravity"] -->|"MCP: stdio or shared daemon :16182"| S["NexusBrowser.exe MCP server (C#, .NET 10)"] S -->|"HTTP 9225, token"| B["Local bridge 127.0.0.1"] B -->|"WebSocket 9224, signed"| X["Chrome extension"] X -->|"DevTools Protocol"| T["Agent's background tabs in your Chrome"]

NexusBrowser.exe is the only engine (C#, .NET 10; the Python one was removed in 2.33.0). A release carries it self-contained for each Windows architecture (NexusBrowser-win-x64.zip, NexusBrowser-win-arm64.zip), with their `SHA256SUMS.tx