Turn Spreadsheets into Software with the Tool Builder Add-in for Excel

Published

March 17, 2026

Tool Builder add-in for Excel is a new tool that lets you run web apps that use your workbook tables as the database.

Why This Matters

Excel is already the world’s most widely distributed data platform. It has:

  • Data: The workbook is the database (no separate server needed).
  • Auth: Sharing the file is the same as sharing the app.
  • Ubiquity: It runs on the web, desktop, and mobile.

Boardflare Tool Builder fills the missing piece: a modern, sandboxed UI layer that lives on top of your spreadsheet data. That means you can deploy real tools without provisioning infrastructure, managing credentials, or asking IT for access.

This is the easiest & cheapest way to deploy user-generated apps that exist today.

How It Works (Generate → Paste → Run)

The workflow is designed to be simple and AI-driven:

  1. Generate a complete app using an AI tool (ChatGPT, Claude, Gemini, etc.).
  2. Paste the generated HTML/JS into the Tool Builder add-in editor.
  3. Run the app instantly inside your workbook.

The AI System Prompt

The Tool Builder add-in includes a System Prompt that tells the AI:

  • How to use the Boardflare Bridge (bf.*) API to read/write workbook tables
  • How to style the UI (Tailwind CSS + responsive layout)
  • How to follow the platform contract so the app runs across Excel, Preview, and Web

Always start a fresh AI chat by pasting the System Prompt first, then ask for your specific app.

What Is a Tool Builder App?

A Tool Builder app is a single-file HTML/JavaScript web application that runs in three contexts:

  • Excel (real workbook tables) — production use
  • Preview (in-memory seed data) — development and testing
  • Web (demo/SEO landing pages) — live demo and discoverability

Every Tool Builder app ships as a web page on boardflare.com, so the live demo is part of distribution, not a separate prototype.

The Core API (window.bf)

Tool Builder apps interact with workbook tables using the bf.* API. The most important operations are:

  • bf.createTable(name, { columns, seed }) — creates a table if it doesn’t exist
  • bf.getRows(name) — reads rows from a table
  • bf.addRow(name, data) — adds a row
  • bf.updateRow(name, rowId, updates) — updates a row
  • bf.deleteRow(name, rowId) — deletes a row
  • bf.onSync(callback) — receives updates when data changes

Tip: Empty cells come back as null, not '' or 0. Use nullish coalescing (??) when computing totals or summaries.

Build Smart Apps (What Makes a Great Tool Builder App)

A great Tool Builder app:

  • Solves a workflow problem that formulas alone don’t handle well
  • Uses workbook tables as the source of truth (not local state)
  • Works across Excel, Preview, and Web without special casing
  • Has visible, testable behavior based on realistic seed data

Sweet Spots

  • ✅ A multi-step workflow (e.g., intake form → list → summary)
  • ✅ A table-backed dashboard with search/filter/sort
  • ✅ A CRUD tool with editable rows and summary cards
  • ✅ A chart that matches the table view

Not an app:

  • ❌ A single formula calculation
  • ❌ A static output with no user interaction

Where to Start

Try an Example

Explore the initial set of example apps at:

https://www.boardflare.com/tools/visualization/

Each example is a complete app you can copy and paste into the add-in, then tweak with AI.

Create with AI

  1. Click “Copy System Prompt” in the add-in.
  2. Open your preferred AI tool, paste the prompt, then ask for your app.
  3. Copy the generated HTML back into the add-in and hit Run.

Managing Your Apps

Storage & Portability

Apps are stored inside the workbook (Document Settings), so:

  • Your app code travels with the file
  • No server storage or user account is required

Version History

The add-in keeps the last 3 versions of your app code. If a change breaks your app, you can restore a previous version via the History button.

Editing & Deleting

  • Edit: Use the settings gear or context menu to open the code editor.
  • Delete: Remove the current app entirely (permanently).

Advanced: Templates, SEO, and Growth

Boardflare aims to build a large library of app templates to cover the long tail of use cases (e.g., dashboards, trackers, project tools). Each template is a standalone HTML app that can be copied into Excel or used as a live demo on the website.

By publishing these templates as web pages, we create SEO landing pages that help users discover the tool and then use the same app inside their workbook.

Troubleshooting

“App Failed to Load”

  1. Check the Error State screen in the add-in.
  2. Click “Copy Error” and paste it back into your AI assistant to ask for a fix.

“Table Not Found”

Make sure your app calls bf.createTable() at startup. The system prompt usually includes this.

Sync Issues

Updates to the workbook are debounced (≈300ms) to prevent performance issues. If you don’t see a change immediately, wait a moment.

Ready to build? Open the Tool Builder add-in and start with one of our example templates or ask an AI to generate a tool for your workflow.