Pi for Excel: AI sidebar add-in for Excel, powered by Pi

Hacker News · Feb 20, 2026 · Collected from RSS

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Pi for Excel Open-source, multi-model AI sidebar add-in for Microsoft Excel. Powered by Pi. Pi for Excel is an AI agent that lives inside Excel. It reads your workbook, makes changes, and does research — using any model you choose. Bring your own API key or OAuth login for Anthropic, OpenAI, Google Gemini, or GitHub Copilot. Features Core spreadsheet tools — 16 built-in tools that the AI can call to interact with your workbook: Tool What it does get_workbook_overview Structural blueprint — sheets, headers, named ranges, tables, charts, pivots read_range Read cells in compact (markdown), CSV, or detailed (with formatting) mode write_cells Write values/formulas with overwrite protection and auto-verification fill_formula AutoFill a formula across a range (relative refs adjust automatically) search_workbook Find text, values, or formula references across all sheets modify_structure Insert/delete rows/columns, add/rename/delete/hide sheets format_cells Apply formatting — fonts, colors, number formats, borders, named styles conditional_format Add or clear conditional formatting rules trace_dependencies Trace formula lineage (precedents upstream or dependents downstream) explain_formula Plain-language formula explanation with cited cell references view_settings Gridlines, headings, freeze panes, tab color, sheet visibility comments Read, add, update, reply, resolve/reopen cell comments workbook_history List/restore automatic in-between-saves backups for workbook mutations instructions Persistent user-level and workbook-level guidance for the AI conventions Configurable formatting defaults (currency, negatives, zeros, decimal places) skills Bundled Agent Skills for task-specific workflows Multi-model support — use any supported provider; switch models mid-conversation: Anthropic (Claude) — API key or OAuth OpenAI / OpenAI Codex — API key Google Gemini — API key GitHub Copilot — OAuth Session management — multiple session tabs per workbook, auto-save/restore, session history, /resume to pick up where you left off. Auto-context injection — the AI automatically receives the workbook blueprint, your current selection, and recent cell changes before every turn. No need to manually describe what you're looking at. Workbook recovery — automatic checkpoints before every mutation. One-click revert from the sidebar if something goes wrong. Formatting conventions — define your house style once (currency symbol, negative style, decimal places) and the AI follows it automatically. Slash commands — /model, /login, /settings, /rules, /extensions, /integrations, /export, /compact, /new, /resume, /history, /shortcuts, and more. Extensions — install sidebar extensions (mini-apps) from chat. The AI can generate and install extension code directly via the extensions_manager tool. Extensions run in an iframe sandbox by default. Integrations — opt-in external tool integrations: Web Search (Serper/Tavily/Brave) + fetch_page — find and read external sources without leaving Excel MCP Gateway — connect to user-configured MCP servers for custom tool access Feature-flagged capabilities (managed via /experimental): Tmux bridge — local terminal control from the sidebar Python / LibreOffice bridge — run Python scripts and convert files locally Files workspace write/delete gate — shared artifact storage across sessions (assistant built-in docs under assistant-docs/ are always available read-only) External skills discovery — opt-in loading of locally configured external SKILL.md sources Advanced extension controls — remote URL opt-in, permission enforcement, sandbox rollback, and Widget API v2 (Web Search + MCP are managed in /integrations.) Install Download manifest.prod.xml Add it to Excel — see install guide for step-by-step instructions (macOS + Windows) Click Open Pi in the ribbon Connect a provider (paste an API key or sign in with OAuth) Start chatting — try What sheets do I have? or Summarize my current selection Developer Quick Start Prerequisites Node.js ≥ 20 mkcert — for local HTTPS (required by Office.js) Setup git clone https://github.com/tmustier/pi-for-excel.git cd pi-for-excel npm install # Generate local HTTPS certs (Office.js requires HTTPS) mkcert -install # one-time CA setup mkcert localhost # creates localhost.pem + localhost-key.pem mv localhost-key.pem key.pem mv localhost.pem cert.pem Run npm run dev # Vite dev server on https://localhost:3000 Then sideload the dev manifest into Excel: macOS (Microsoft docs): cp manifest.xml ~/Library/Containers/com.microsoft.Excel/Data/Documents/wef/ Then open Excel → Insert → My Add-ins → Pi for Excel. Windows (Microsoft docs): Open Excel → Insert → My Add-ins → Upload My Add-in → select manifest.xml. The dev manifest points to https://localhost:3000. The production manifest (manifest.prod.xml) points to the hosted Vercel deployment. Useful commands Command Description npm run dev Start Vite dev server (port 3000, HTTPS) npm run build Production build → dist/ npm run check Lint + typecheck + CSS theme checks npm run typecheck TypeScript type checking only npm run lint ESLint npm run test:models Unit tests — model ordering npm run test:context Unit tests — tools, context, sessions, extensions, integrations npm run test:security Security policy tests — proxy, CORS, sandbox, OAuth npm run proxy:https CORS proxy for OAuth flows (default https://localhost:3003) npm run validate Validate the Office add-in manifest CORS proxy Some OAuth token endpoints are blocked by CORS inside Office webviews. If OAuth login fails: User setup command: npx pi-for-excel-proxy (or curl -fsSL https://piforexcel.com/proxy | sh if Node is missing) Dev/source setup command: npm run proxy:https (defaults to https://localhost:3003) In Pi → /settings → Proxy → enable and set the URL Retry login API-key auth generally works without the proxy. Local bridges (Python / tmux) Use one-command local bridge helpers: Python / LibreOffice bridge: npx pi-for-excel-python-bridge (default URL https://localhost:3340, real mode) tmux bridge: npx pi-for-excel-tmux-bridge (default URL https://localhost:3341, real mode) In Pi, these localhost bridge URLs are used by default. Configure /experimental ...-bridge-url only when you want a non-default URL. Real-mode prerequisites: python3 must be installed for python_run / python_transform_range LibreOffice (soffice or libreoffice) is required for libreoffice_convert tmux is required for the tmux bridge real mode Optional assisted install (macOS/Homebrew): npx pi-for-excel-python-bridge --install-missing npx pi-for-excel-tmux-bridge --install-missing Manual macOS install: brew install tmux brew install --cask libreoffice To force safe simulated mode instead: PYTHON_BRIDGE_MODE=stub npx pi-for-excel-python-bridge TMUX_BRIDGE_MODE=stub npx pi-for-excel-tmux-bridge Source-checkout alternatives remain available via npm run python:bridge:https and npm run tmux:bridge:https. Architecture Pi for Excel is a single-page Office taskpane add-in built with: Vite — dev server + production bundler Lit — web components for the sidebar UI pi-agent-core — agent runtime (tool loop, streaming, state management) pi-ai — multi-provider LLM abstraction (Anthropic, OpenAI, Google, GitHub Copilot) pi-web-ui — shared web UI components (message rendering, storage, settings dialogs) Office.js — Excel workbook API Source layout src/ ├── taskpane/ # App init, session management, tab layout, context injection ├── taskpane.html # Entry HTML (loads Office.js + taskpane.ts) ├── taskpane.ts # Entry script ├── boot.ts # Pre-mount setup (CSS, patches) ├── tools/ # 16 core tools + feature-flagged tools + registry ├── prompt/ # System prompt builder ├── context/ # Workbook blueprint cache, selection/change tracking ├── auth/ # OAuth providers, API proxy, credential restore ├── models/ # Model ordering + version scoring ├── ui/ # Sidebar component, tool renderers, theme CSS │ └── theme/ # Design tokens, component styles (DM Sans + teal-green palette) ├── commands/ # Slash command registry + builtins ├── extensions/ # Extension store, sandbox runtime, permissions ├── integrations/ # Web Search + MCP Gateway integration catalog ├── skills/ # Agent Skills catalog + runtime loader ├── experiments/ # Feature flag definitions + toggle logic ├── workbook/ # Workbook identity (hashed), session association, coordinator ├── conventions/ # Formatting defaults (currency, negatives, dp) ├── rules/ # Persistent user/workbook rules store ├── compaction/ # Auto-compaction thresholds + logic ├── storage/ # IndexedDB initialization ├── files/ # Files workspace (read/list always on; write/delete feature-gated) ├── audit/ # Workbook change audit log ├── messages/ # Message conversion helpers ├── debug/ # Debug mode utilities ├── stubs/ # Browser stubs for CSP/Node-only deps (Ajv, Bedrock, stream, etc.) ├── compat/ # Compatibility patches (Lit, marked, model selector) └── utils/ # Shared helpers (HTML escape, type guards, errors) scripts/ # Dev helpers — CORS proxy, tmux/python bridges, manifest gen pkg/proxy/ # Publishable npm CLI package: `pi-for-excel-proxy` pkg/python-bridge/ # Publishable npm CLI package: `pi-for-excel-python-bridge` pkg/tmux-bridge/ # Publishable npm CLI package: `pi-for-excel-tmux-bridge` tests/ # Unit + security tests (~50 test files) docs/ # Current docs (install/deploy/features/policy) + archive/ for historical plans skills/ # Bundled Agent Skill definitions (web-search, mcp-gateway) public/assets/ # Add-in icons (16/32/80/128px) Key design patterns Tool registry as single source of truth — src/tools/registry.ts defines all core tool names and construction. UI renderers, input humanizers, and prompt docs all derive from it. Workbook coordinator — serializes mutating tool calls per-workbook to prevent concurrent writes from multiple session tabs. Auto-context — the workbook blueprint, selection state, and recent changes are injected before each user message so the AI always knows what it's looking at. Execution policy — each to