Tandem Browser

A programmable workspace where human intent and AI capability meet — on the web that already exists.

Tandem is a local-first Electron browser that shifts the AI from a sidebar next to your browser into the browser itself. Same tabs, same cookies, same logged-in sessions, same page you are looking at right now. The agent reads the accessibility tree, watches the live network, can rewrite the UI of the site you are on, and hands back to you when something needs a human. You are both in one runtime.

That shift matters because it is what makes a bunch of things actually possible for the first time:

• Automate real SaaS without an API — Gmail, Coolblue, Funda, your bank's portal, your internal admin tool. If you can use it in a browser, your agent can use it in Tandem, in your real logged-in session.
• Rewrite live UI on any site — “add a price-per-square-meter column to this listing view” becomes a userscript the agent injects into the real page while you keep scrolling.
• See beyond pixels — accessibility tree + DOM + live network log + DevTools. The agent can answer “what API did this page just hit and what came back?” without anything leaving your machine.
• Real co-browsing — you and one or more agents in the same browser at the same time, across tabs and workspaces, with tab locks and explicit handoffs.
• Cold-start usable — point a capable model (Claude, Cursor, a local Ollama model) at a fresh Tandem install and a normal web task works on day one. No per-site recipes to author, no retrain-per-flow phase.
• Bring any AI — Tandem is model-agnostic. Any agent that speaks MCP or HTTP works — Claude, GPT, Gemini, local Ollama, LM Studio, custom scripts. Swap models when a cheaper or faster one ships. Run two at once. Go fully offline with a local model. The browser doesn't care which brain you plug in.

It works on the web that already exists — no site has to opt in, no new protocol has to land. Agents connect on the same machine or remotely over Tailscale, and multiple agents can share one browser without stepping on each other. An 8-layer security perimeter sits between web content and the agent layer, because when an AI has access to a real browser, a hidden instruction in a page is remote code execution without an exploit.

Connect via MCP (Claude Code, Claude Desktop, Cursor, Windsurf, Ollama, any MCP client) or a 300+ endpoint HTTP API. The everyday version of the pitch: it feels like going on the internet with a brilliant teammate — not like using a chatbot parked next to a browser.

What Tandem is not

• Not an AI sidebar. A chat panel next to a browser still leaves the AI outside the page.
• Not RPA or pixel automation. No brittle coordinates, no record-and-replay macros. The agent works with structure.
• Not screenshot-driven automation. Screenshot loops are slow, fragile, and expensive. Tandem gives the agent the page as semantic structure first.
• Not just another Chromium wrapper. This is a daily-driver browser with a serious security perimeter around a first-class agent layer.
• Not “chat with this webpage.” The agent opens tabs, fills forms, logs in, hands back for a CAPTCHA, injects a userscript, and comes back to finish — as one continuous piece of work.
• Not a cloud service. Your browser, your machine, your sessions, your data. There is no Tandem backend.

What's new now

Tandem Browser now supports:

• local MCP and local HTTP access
• remote MCP over Tailscale
• remote HTTP over Tailscale
• multiple agents connected to the same browser at once
• in-product pairing and onboarding through Settings -> Connected Agents

Want the fastest path in?

• Try Tandem locally -> Quick Start
• Read the docs and API surfaces -> docs/ and docs/INDEX.md
• Ask questions or share workflows -> GitHub Discussions
• Support development -> GitHub Sponsors

What Can An Agent Do?

257 tools total — full parity with the HTTP API.

Why Not Just Use Playwright?

Playwright gives you a headless browser that you control. Tandem Browser gives you the user's real browser — their tabs, their sessions, their cookies, their extensions. The agent doesn't start from scratch; it joins what's already there.

Plus:

• Security model: 8 layers between web content and the agent, including prompt injection defense. Playwright has none.
• Shared context: the agent sees what the human is doing and vice versa
• Stealth: websites see a normal Chrome browser, not an automation tool
• Background tabs: operate on any tab without stealing focus
• Human-in-the-loop: captchas, risky actions, and ambiguous cases go back to the human

Tandem Browser vs WebMCP

WebMCP is an important new idea, but it solves a different layer of the stack.

WebMCP helps websites become more agent-readable. Tandem Browser helps humans and agents work together in the real browser, across the web.

These ideas can coexist. Tandem Browser is not anti-WebMCP. If more sites expose cleaner agent surfaces, great. But Tandem Browser's job is broader: shared human-AI browser work, local-first control, and governance around what the agent is doing.

For the longer version, see docs/tandem-browser-vs-webmcp.md.

Quick Start

macOS Apple Silicon (M1+) — download the signed and notarized binary:

Download Tandem Browser v1.0.0 →

1. Open the .dmg, drag Tandem Browser to Applications, launch it
2. Open Settings → Connected Agents and scroll to Connect your AI to Tandem
3. Choose On this machine or On another machine
4. Click Generate connection instructions
5. Click Copy instructions and paste into your AI agent

That's it. Tandem publishes its own bootstrap surface — the agent reads /agent and connects automatically.

Windows 11 x64 — download the installer or portable build:

Download Tandem Browser v1.11.0 →

Windows builds are official Tandem Browser downloads, but they are currently unsigned. Windows may show an unknown publisher or SmartScreen warning during install. Code signing is planned, but Windows is supported now.

Building from source

For Linux, Windows, macOS, or if you want to hack on Tandem itself:

git clone https://github.com/hydro13/tandem-browser.git
cd tandem-browser
npm install
npm start

macOS and Windows are supported platforms. Linux is best-effort.

Start Here

Depending on what you want to do:

• Install Tandem -> download macOS v1.0.0 or Windows v1.11.0, or follow Quick Start above
• Connect an agent -> see Connect Your AI Agent
• Explore the API and docs -> browse docs/ and docs/INDEX.md
• See the product story and website -> visit tandembrowser.org
• Ask questions or share workflows -> join GitHub Discussions
• Support development -> sponsor Tandem on GitHub Sponsors

Connect Your AI Agent

Tandem is model-agnostic. Any agent that speaks MCP or HTTP works — Claude, GPT, Gemini, local Ollama, LM Studio, custom scripts. Swap models, combine models, run fully offline. The browser does not care which AI you bring.

Tandem supports AI agents running on the same machine or on a remote machine over a private Tailscale network. Both can be active at the same time.

The primary onboarding flow is now inside Tandem itself:

1. Open Settings -> Connected Agents
2. Choose On this machine or On another machine
3. Let Tandem generate the connection instructions
4. Paste those instructions into your AI agent

Tandem handles the setup-code flow and publishes its own bootstrap/discovery surface for the agent at /agent, /agent/manifest, /agent/version, and /skill. New paired agents must read /skill, /agent/manifest, and /agent/bootstrap with their binding token before normal API/MCP use; Tandem returns 428 agent_startup_required when that startup sequence is skipped.

The Agent API port defaults to 8765 and can be changed in Settings -> Connected Agents -> Agent API settings. Local clients should discover the current port from ~/.tandem/api-port or ~/.tandem/api-endpoints.json. ~/.tandem/api-token remains the readable local token compatibility contract.

On the same machine (MCP or HTTP)

If your AI runs on the same machine as Tandem, the simplest path is:

1. Open Settings -> Connected Agents
2. Choose On this machine
3. Copy the generated instructions into your AI

MCP — Add to your MCP client configuration (Claude Code, Claude Desktop, Cursor, Windsurf, or any MCP client):

{
  "mcpServers": {
    "tandem": {
      "command": "node",
      "args": ["/path/to/tandem-browser/dist/mcp/server.js"]
    }
  }
}

Start Tandem, and 257 tools are available immediately.

HTTP API — Use the local API token directly:

API_PORT="$(cat ~/.tandem/api-port 2>/dev/null || printf 8765)"
API="http://127.0.0.1:${API_PORT}"
TOKEN="$(cat ~/.tandem/api-token)"

curl -sS "$API/status"
curl -sS "$API/tabs/list" \
  -H "Authorization: Bearer $TOKEN"

300+ endpoints for everything the MCP tools can do, plus lower-level access.

On another machine (Tailscale)

Remote agents connect over a private Tailscale network. Both machines must be on the same tailnet. Tandem is never exposed to the public internet.

1. Open Settings -> Connected Agents
2. Choose On another machine
3. Tandem detects the Tailscale address and generates a ready-to-use instruction block
4. Paste that instruction block into your remote AI agent
5. The AI reads /agent, exchanges the setup code for a permanent token, and connects

The token stays valid until you pause, revoke, or remove it from the Connected Agents UI.

MCP (recommended for Claude Code, Cursor, and other MCP clients):

{
  "mcpServers": {
    "tandem": {
      "type": "streamable-http",
      "url": "http://<tandem-tailscale-ip>:<configured-port>/mcp",
      "headers": {
        "Authorization": "Bearer <your-binding-token>"
      }
    }
  }
}

HTTP API works the same way as local, using the binding token as Bearer auth.

Both transports give remote agents the same 257 tools and 300+ endpoints as local agents.

# Exchange setup code for token
curl -X POST http://<tandem-tailscale-ip>:<configured-port>/pairing/exchange \
  -H "Content-Type: application/json" \
  -d '{"code":"TDM-XXXX-XXXX","machineId":"...","machineName":"...","agentLabel":"...","agentType":"..."}'

# Use the returned token
curl -sS http://<tandem-tailscale-ip>:<configured-port>/status \
  -H "Authorization: Bearer <token>"

Discovery

A running Tandem instance publishes its own version-matched discovery surface:

• GET /agent — human-readable bootstrap page
• GET /agent/manifest — machine-readable endpoint manifest
• GET /skill — version-matched usage guide

These are public (no auth required) and use the request Host header, so they return correct URLs whether accessed locally or over Tailscale on the configured port.

Security Model

Tandem Browser treats security as core architecture, not an afterthought. When an AI has access to your browser, every ad network, tracking pixel, and malicious domain is in the agent's attack surface.

8 security layers:

1. Network shield with domain/IP blocklists
2. Outbound guard scanning POST bodies for credential leaks
3. AST-level JavaScript analysis on runtime scripts
4. Behavior monitoring per tab
5. Gatekeeper channel for ambiguous cases
6. Prompt injection defense on page content
7. Layer separation — pages cannot fingerprint the agent
8. Human-in-the-loop for risky or blocked actions

Strict layer separation means page JavaScript cannot observe or fingerprint the agent layer. That's not something you bolt onto Chrome after the fact.

The Browser

Beyond the agent layer, Tandem Browser is a full daily-driver browser:

• Left sidebar: Telegram, WhatsApp, Discord, Slack, Gmail, Calendar, Instagram, X — all in isolated sessions alongside your browsing
• Workspaces: organize tabs into separate spaces (the agent gets its own)
• Pinboards: collect and organize links, images, quotes
• Bookmarks & History: with Chrome import and sync
• Chrome extensions: load from disk or install from Chrome Web Store
• URL autocomplete: Chrome-style suggestions from browsing history
• Password manager: local vault with AES-256-GCM encryption
• Video recorder: application and region capture
• Device emulation: test responsive designs

All local-first. No cloud dependency.

Typical Agent Workflows

• Research: agent opens multiple tabs, reads and summarizes pages while you keep browsing
• Autonomous workspace: agent creates its own workspace, manages tabs independently, and alerts you when human help is needed
• SPA inspection: accessibility snapshots and semantic locators instead of guessing from raw HTML
• Session-aware tasks: agent operates inside your real authenticated browser context
• Live previews: agent builds HTML pages and shows them to you in the browser with instant live reload

Status

Public developer preview — real project, early public state, open for contributors, not yet a polished mass-user release.

• Primary platform: macOS Apple Silicon
• Supported platform: Windows 11 x64
• Secondary platform: Linux
• Binaries: signed and notarized macOS Apple Silicon builds plus unsigned Windows x64 installer/portable builds on GitHub Releases, starting with Windows in v1.10.0
• Current version: 1.11.0
• Package metadata: package.json

Community

Have a question, idea, or want to show what you've built with Tandem Browser? Join GitHub Discussions.

• Q&A — troubleshooting, "how do I…" questions
• Ideas — feature proposals before they become issues
• Show and Tell — your setups, workflows, and screenshots

For bugs and concrete feature requests, open an issue.

If Tandem Browser is useful to you, or relevant to your company, sponsorship directly funds continued development and security work: GitHub Sponsors.

Contributing

Good contribution areas:

• MCP tool improvements and new tool proposals
• Browser API improvements
• Linux quality and cross-platform testing
• Security review and hardening
• UI polish for human + agent workflows
• Bug reports with reproduction steps

Start with CONTRIBUTING.md and PROJECT.md.

Repository Guide

License

MIT. See LICENSE.