Recalculate a Workbook

Load workbook bytes, change inputs, recalculate, and save new bytes. No desktop application is involved.

Test with a real workbook early

Single-formula tests prove the package loads. A representative workbook proves whether file structures, formulas, and locale assumptions fit your use case.

Bytes in, bytes out: the host owns the files, and save() does not recalculate.

JavaScript / WASM

import createFormulon from '@libraz/formulon'

const Module = await createFormulon()
const workbook = Module.Workbook.loadBytes(xlsxBytes)
const check = (status: { ok: boolean; message: string; context: string }) => {
  if (!status.ok) throw new Error(`${status.message}: ${status.context}`)
}

try {
  if (!workbook.isValid()) {
    throw new Error(Module.lastErrorMessage())
  }

  check(workbook.setExcelProfileId('win-365-en_US'))
  check(workbook.setPinnedNow(2026, 10, 9, 9, 30, 0))
  check(workbook.setNumber(0, 3, 1, 125000)) // sheet 0, B4
  check(workbook.recalc())

  const saved = workbook.save()
  if (!saved.status.ok || saved.bytes === null) {
    throw new Error(`${saved.status.message}: ${saved.status.context}`)
  }

  await upload(saved.bytes)
} finally {
  workbook.delete()
}

Python

python

from formulon import Workbook

with open("input.xlsx", "rb") as f:
    blob = f.read()

with Workbook.load(blob) as wb:
    wb.set_excel_profile_id("win-365-en_US")
    wb.set_pinned_now(2026, 10, 9, 9, 30, 0)
    wb.set_number(0, 3, 1, 125000.0)
    wb.recalc()
    output = wb.save()

with open("output.xlsx", "wb") as f:
    f.write(output)

CLI

formulon recalc --profile win-365-en_US --now 2026-10-09T09:30:00 input.xlsx -o output.xlsx
formulon dump --profile win-365-en_US --now 2026-10-09T09:30:00 --values output.xlsx

The profile and the pinned clock are runtime state: neither is saved in the output file, so set both again after every load. setPinnedNow fixes what NOW(), TODAY() and relative date filters read, which keeps date-dependent results reproducible.

Call recalc() successfully before saving when every formula cache in the workbook must be current. Saving writes the values currently held by the workbook; it does not run a recalculation itself. A partial recalculation may leave formula caches outside its requested dependency closure unchanged. Saving keeps the workbook structures Formulon models and passes through parts it does not model. What survives depends on the container and the feature; check File format support and the save diagnostics. Saving the same unchanged in-memory workbook twice produces identical bytes because each saved archive entry uses a fixed timestamp; this does not mean the output bytes match the original input file.

Run the round trip here

The panel below runs the same sequence in the browser. Pick a workbook, or let it generate a sample; the bytes are parsed with loadBytes(), recalculated, and saved back to .xlsx bytes you can download. The sheet under the panel reopens those saved bytes in an embedded formulon-cell grid, so the values on screen are what the engine computed, not the values cached in the original file.

Load an xlsx and recalculate it

Nothing is uploaded. Parsing, recalculation and serialization all happen in this page’s WASM engine, and the bytes never leave your browser.

Recalculate a Workbook ​

JavaScript / WASM ​

Python ​

CLI ​

Run the round trip here ​

Recalculate a Workbook

JavaScript / WASM

Python

CLI

Run the round trip here