> ## Documentation Index
> Fetch the complete documentation index at: https://docs.doconda.com/llms.txt
> Use this file to discover all available pages before exploring further.

# What is an XLSX file

> XLSX is Microsoft Excel's workbook format since 2007: a ZIP package of XML (SpreadsheetML) from the Office Open XML standard.

**XLSX** is Microsoft Excel's default workbook format since Excel 2007. It is a ZIP package that follows the
[Office Open XML](/en/glossary/ooxml) standard (SpreadsheetML): each sheet is an XML part, and each cell can hold a value,
a formula and that formula's last calculated result. Styles, defined names and charts live in their own parts.

## Why it matters when generating documents with AI

* A useful sheet stores [formulas](/en/glossary/spreadsheet-formulas), not just numbers: change one input and the rest
  recalculates.
* Numbers or dates stored as text don't sum or sort correctly, even though they look the same.
* Errors such as `#REF!` or `#DIV/0!` and broken references only show up when the workbook is calculated.
* A language model can write plausible but made-up figures; formulas make it visible where each result comes from.

## With Doconda

With `format: "xlsx"`, Doconda creates an Excel workbook with real formulas (not pasted numbers), with assumptions in
their own cells and no calculation errors, plus its PDF ([Create](/en/guides/create)). When [editing](/en/guides/edit),
changes are made with formulas too. When [reviewing](/en/guides/review), it detects formula errors, numbers stored as
text, hidden data and inconsistent formulas, and gives the sheet and cells.

## Related

* [Formulas in a generated XLSX](/en/glossary/spreadsheet-formulas)
* [What is OOXML](/en/glossary/ooxml)
* [Structured output vs file output](/en/glossary/structured-output)


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