Show HN: Tandem, real-time collaboration with Claude Code

An AI document reviewer — open a progress report, RFP, or compliance filing and Claude reviews it alongside you in real time. Highlights, comments, suggestions, and questions appear as first-class annotations you accept, dismiss, or discuss. The original file is never modified unless you save. - Node.js 22+ (download) - Claude Code ( irm https://claude.ai/install.ps1 | iex ) npm install -g tandem-editor tandem setup # registers MCP tools + installs Claude Code skill tandem # starts server + opens browser tandem setup auto-detects Claude Code and Claude Desktop, writes MCP configuration, and installs a skill (~/.claude/skills/tandem/SKILL.md ) that teaches Claude how to use Tandem's tools effectively. Re-run after upgrading (npm update -g tandem-editor && tandem setup ). Start Claude Code with channel push for real-time notifications: claude --dangerously-load-development-channels server:tandem-channel Then try: "Review the welcome document with me" Claude calls tandem_open , the document appears in the browser, and annotations start flowing. Chat messages, annotation actions, and text selections push to Claude instantly. Without channels: Use the /loop skill in Claude Code to poll: /loop 30s check tandem inbox and respond to any new messages npm run doctor # checks Node.js, MCP config, server health, ports Or check the raw health endpoint: curl http://localhost:3479/health # → {"status":"ok","version":"0.1.2","transport":"http","hasSession":false} hasSession becomes true once Claude Code connects. Development Setup (contributing / building from source) git clone https://github.com/bloknayrb/tandem.git cd tandem npm install npm run dev:standalone # starts server (:3478/:3479) + browser client (:5173) Open http://localhost:5173 — you'll see sample/welcome.md loaded automatically on first run. The .mcp.json in the repo configures Claude Code automatically when run from this directory. Claude adds highlights, comments, suggestions, and flags directly in the document. The side panel lists all annotations with filtering by type, author, and status. Accept, dismiss, or edit each one individually — or use bulk actions to process them in batches. Send freeform messages to Claude alongside annotation review. Select text before sending to attach it as a clickable anchor — clicking it later scrolls back to that passage. Press Ctrl+Shift+R to enter keyboard review mode. Navigate with Tab, accept with Y, dismiss with N, examine with E. A 10-second undo window lets you reverse accidental accepts. The side panel tracks your position. - Multi-document tabs — open .md ,.txt ,.docx files side by side; drag to reorder - .docx review-only mode — open Word documents for annotation; imported Word comments appear alongside Claude's - Session persistence — documents and annotations survive server restarts - Real-time channel push — annotation actions, chat, and selections push to Claude instantly - Keyboard shortcuts — press ? for the full reference - Unsaved-changes indicator — dot on tab title when a document has pending edits - Configurable display name — set your name so Claude knows who's reviewing - Atomic file saves — write to temp, then rename, preventing partial writes - E2E tested — Playwright tests cover the annotation lifecycle end-to-end - User Guide — How to use Tandem: browser UI, annotations, chat, review mode, keyboard shortcuts - MCP Tool Reference — 30 MCP tools + channel API endpoints - Architecture — System design, data flows, coordinate systems, channel push - Workflows — Claude Code usage patterns: document review, cross-referencing, multi-model - Roadmap — Phase 2+ roadmap, known issues, future extensions - Design Decisions — ADR-001 through ADR-021 - Lessons Learned — 31 implementation lessons | Command | What it does | |---|---| tandem | Start server and open browser (global install) | tandem setup | Register MCP tools with Claude Code / Claude Desktop | tandem setup --force | Register to default paths regardless of auto-detection | tandem --version | Show installed version | tandem --help | Show usage | Tandem uses two MCP connections: HTTP for document tools (28 tools including annotation editing), and a channel shim for real-time push notifications. Global install (tandem setup ): Automatically writes both entries to ~/.claude/mcp_settings.json (Claude Code) and/or claude_desktop_config.json (Claude Desktop) with absolute paths. No manual configuration needed. Development setup (.mcp.json ): The repo includes a .mcp.json that configures both entries automatically when Claude Code runs from the repo directory: { "mcpServers": { "tandem": { "type": "http", "url": "http://localhost:3479/mcp" }, "tandem-channel": { "command": "npx", "args": ["tsx", "src/channel/index.ts"], "env": { "TANDEM_URL": "http://localhost:3479" } } } } Both entries are cross-platform — no platform-specific configuration needed. All optional — defaults work out of the box. | Variable | Default | Description | |---|---|---| TANDEM_POR