Status: Under active development. Not yet ready for production use. APIs, file layout, and packaging may change without notice until the first tagged release.
Formulon is a headless, Excel-compatible calculation engine — a C++17 core that aims to be bit-exact against Mac Excel 365 (ja-JP), with every known divergence explicitly tracked. The same engine is packaged for the browser (WebAssembly), for Python, and for native command-line use, so a workbook recalculates to the same values wherever it runs.
No Excel installation, no Microsoft runtime, no COM automation required. Runs on macOS, Linux, Windows, in the browser, and in Node.
- Strict oracle, not aspirational compatibility. Mac Excel 365 (ja-JP)
is the behavioral oracle. Outputs are checked for bit-level parity against
golden data regenerated from the real product; every accepted divergence
(transcendental ulp drift, volatile-function snapshots, Excel quirks where
Formulon deliberately keeps a saner answer) is recorded case-by-case in
tests/divergence.yamlwith a reason and the last verified Excel build. - One C++ core, identical results everywhere. JS-only competitors re-run the logic in the browser and the logic on the server. Formulon ships one engine to every surface (WASM, Python, CLI) so there is no second implementation to drift.
- Strict WASM size budget. Target 1.65 MB uncompressed / 530 KB Brotli, hard ceiling 1.8 MB / 600 KB Brotli. The budget is enforced in CI, not aspirational; features ship within the budget or do not ship.
- Small dependency set. Engine deps:
miniz(zip),pugixml(XML + XPath 1.0). That is the complete list for the core. Linear algebra, number formatting, and UTF-8 handling are in-tree. - Readable, reviewable code.
Expected<T, Error>error handling, RAII,-fno-exceptions -fno-rtti, Google C++ style.
Anywhere a spreadsheet needs to be computed without booting Excel:
- running
.xlsxworkbooks headlessly in batch jobs or data pipelines, - evaluating Excel-style formulas inside a web application, in the browser,
- embedding calculation into internal tools, bots, or notebooks,
- validating formulas and migrating legacy spreadsheets.
Formulon deliberately does not cover:
| Area | Reason |
|---|---|
| VBA execution | Security. vbaProject.bin is preserved byte-for-byte, never executed. |
Legacy .xls (BIFF8, Excel 97–2003) |
Out of scope for Excel 365 compatibility. |
| Chart / drawing rendering | Belongs to a rendering layer, not the engine. |
| PowerQuery (M) / DAX | Separate engine, separate problem domain. |
| Pivot cache recomputation | Structurally preserved; recomputation is out of scope. |
| Spreadsheet UI | A thin UI integration layer is planned; rendering is yours. |
These are permanent non-goals, not "not yet." The scope is finite on purpose.
| Surface | Name | Notes |
|---|---|---|
| npm | @libraz/formulon |
WASM ESM module, type definitions included. Node 18+, browsers, workers. |
| PyPI | formulon |
CPython 3.9–3.13 wheels for macOS / Linux / Windows. ctypes-based, stdlib-only at runtime. |
| GitHub Releases | formulon-cli-<os>-<arch> |
Standalone CLI binaries (eval, recalc, dump). |
As of 2026-05: all 522 catalogued Excel functions are implemented (100%) across Math & Trig, Statistical, Logical, Text, Date/Time, Lookup, Financial, Engineering, Information, Database, Cube, and the 2024/2025 additions (GROUPBY, PIVOTBY, TRANSLATE, COPILOT, ...). 92 oracle categories are defined and regenerated from Mac Excel 365 ja-JP. A bytecode compiler and stack-machine VM run in parallel with the tree-walker for parity verification. The OOXML reader/writer round-trips sheets, styles, conditional formatting, comments, hyperlinks, merges, data validations, defined names, tables, and pivot tables; an MS-XLSB reader/writer is in place. Workbook-level operations (sheet add / rename / move, row/column insert / delete with formula rewriting, partial recalc, iterative-solver progress callbacks) are wired through the C ABI and exposed in the WASM, Python, and CLI surfaces.
Feedback, issue reports, and oracle divergence reports are welcome, but please do not rely on Formulon for production workloads yet.
The fastest way to help right now is to donate Excel oracle data
from your locale. If you have Excel 365 in any locale beyond Mac
ja-JP, one command (make oracle-contribute) drives Excel, captures
goldens, and walks you through the PR. See
CONTRIBUTING.md for the full flow and the rationale
for why this is community-driven.