IronCalc
Free, open-source spreadsheet calculation engine you embed in your own app (Rust, WASM).
🔗 Visit IronCalc
Description
IronCalc is a free, open-source engine that does the number-crunching part of a spreadsheet — formulas, formatting, multiple sheets — without any of the app around it, so a developer can drop it into their own product the way you'd drop a calculator chip into a calculator. Think of it as the "brain" of Excel or Google Sheets, minus the toolbar and the price tag, small enough to run entirely inside a web browser.
Built in Rust, IronCalc supports over 300 spreadsheet functions, .xlsx import/export, and multi-sheet workbooks, and ships with Python, JavaScript and WebAssembly bindings so it can be embedded in a web app, a data pipeline, or a desktop tool. It's dual-licensed under MIT and Apache 2.0, meaning there are no runtime fees, no vendor lock-in, and no restrictions on commercial use.
💬 Our review
The short version: if you need actual spreadsheet formula logic inside your own app — not a full spreadsheet UI, just the calculation engine — IronCalc is a serious, free option that didn't exist in open source at this quality level before.
Its strength is scope discipline: it does formula evaluation and .xlsx compatibility well, in a small Rust binary that compiles to WebAssembly, rather than trying to be a whole spreadsheet application. That makes it a good fit for developers building internal tools or data products that need "a bit of Excel" without paying for a commercial embeddable-spreadsheet SDK. The tradeoffs are real: at roughly 4k GitHub stars it's young compared to established commercial engines, there's no bundled UI, and teams needing pixel-perfect Excel-formula parity on edge cases should test their specific formulas before committing.
💰 Pricing
📊 Global score
🤖 AI-enriched data
100% free, open source (MIT/Apache 2.0) — no paid tier
Pros
Free and open source
Runs in-browser via WebAssembly
300+ spreadsheet functions
.xlsx import/export
Cons
Young project (~4k stars)
No built-in spreadsheet UI
Edge-case Excel formula parity not guaranteed