ProvenSheet

Turns the Excel workbook a business runs on into a shared, multi-user web application — and proves every formula still computes exactly what Excel computed.

An uploaded workbook is extracted once into a JSON schema, IronCalc recomputes every formula client-side via WebAssembly, and only user-entered cell values are stored — as a diff against the schema rather than a full copy of the sheet. Before anyone relies on it, every formula is recomputed server-side and compared against the value Excel cached in the file, and you are told per cell what matches.

SWAG Estimates — an industrial construction estimating workbook of 18 sheets and 5,121 formulas, all verified against Excel — ships as the built-in sample.

How it works

• Workbook as schema — the source Excel workbook is extracted once into a JSON schema that defines the sheet structure and formulas.
• Client-side recalculation — IronCalc (MIT / Apache-2.0) runs as WASM in the browser and recomputes formulas without a server round trip.
• Diff-based storage — only the cell values a user actually enters are persisted, keeping stored documents small and the schema authoritative.
• Fidelity verification — a server-side verifier uses IronCalc's native Node bindings to confirm browser results match the original workbook.

Stack

• Next.js 16 — App Router; proxy.ts handles optimistic auth redirects, with real enforcement in src/lib/auth/dal.ts
• Auth.js v5 — JWT sessions via the credentials provider; signup creates a User, a Tenant, and an OWNER Membership

Guides

Guide	What it covers
Working with documents	Adding a workbook, the row actions, the grid, offline sync
Workbook templates	Adding workbooks and fidelity verification
Your workspace and team	Sign-in, passkeys, members, and billing