Convert Excel to Markdown (or CSV)

Turn .xlsx workbooks into Markdown tables you can paste anywhere — or flip one switch and get plain CSV, the most token-efficient format for sheet data. All conversion happens on your Mac.

How to convert a spreadsheet

Drop the .xlsx into Milldown.Multi-sheet workbooks convert every sheet, each under its own heading.
Choose your output: Markdown tables (readable) or CSV (compact).Options → Output → "Spreadsheets as CSV". Multi-sheet workbooks get clear per-sheet markers.
Copy or save — CSV exports save as a proper .csv file.

Markdown table or CSV — which should you use?

Choose	When
Markdown tables	Human readers: documentation, Obsidian notes, GitHub READMEs, anywhere the table should render.
CSV mode	Machine consumers: AI prompts, data pipelines, re-import into other tools. In our benchmark CSV uses 12–29% fewer tokens than the same data as a Markdown table.

Note: for pure sheet data, Markdown tables are actually more token-expensive than CSV — all those pipes add up. That's exactly why Milldown offers both and shows the token count either way.

Details

Formulas convert as their last computed values. Cell formatting (colors, borders) is presentation, not content, and isn't carried across. Legacy .xls files: re-save as .xlsx first.

The two output modes, on real data

The same transaction log from our benchmark corpus, both ways:

Markdown table — for humans

| Order ID | Date | Region | Product |
| --- | --- | --- | --- |
| ORD-2026-00001 | 2026-07-12 | AMER | Starter |
| ORD-2026-00002 | 2026-05-02 | LATAM | Professional |

CSV mode — for models

Order ID,Date,Region,Product
ORD-2026-00001,2026-07-12,AMER,Starter
ORD-2026-00002,2026-05-02,LATAM,Professional

Identical data; the pipes and alignment rows are pure formatting cost. On the full 400-row sheet: 15,298 tokens as a Markdown table, 11,901 as CSV — 22% lighter. One toggle.

What happens to your sheets

Every sheet, not just the first. A multi-sheet workbook converts in full. In Markdown mode each sheet arrives under its own ## Sheet name heading; in CSV mode each is introduced by # Sheet: name. A single-sheet workbook in CSV mode emits bare CSV with no header at all, so it drops straight into a parser.
Formula cells become their results. You get the value the formula last produced, not the formula text — which is almost always what you want to hand a model.
Empty cells stay empty rather than collapsing, so columns stay aligned with their headers.
Your file is never modified. The workbook is opened read-only and closed immediately.

The one thing to check first

If a workbook has never been opened in a spreadsheet application, formula cells can come out blank. Excel stores the last calculated value alongside each formula, and that cached value is what conversion reads. A file generated by a script, or exported by a system that writes formulas without evaluating them, has no cached values to read. Open it once in Excel, Numbers or LibreOffice, save, and convert again — every value will be there. Files you have actually worked in are unaffected, which is the overwhelming majority of them.

Where it struggles

Blank cells look different in each mode. Markdown mode renders an empty cell as NaN and an unlabelled column as Unnamed: 1; CSV mode leaves both genuinely empty. If your sheet has gaps, CSV is the tidier output.
Merged cells and multi-row headers flatten. A sheet with a two-storey header comes out as two ordinary rows, and you may want to tidy the top of the table before using it.
Charts, images and pivot tables are not carried over. Cell data converts; the chart drawn from it does not.
Conditional formatting and cell colour carry no meaning in Markdown. If red means “overdue” in your sheet, that fact is lost — put it in a column instead.
Wide sheets read badly as Markdown tables. Past roughly a dozen columns, CSV mode is easier for both you and the model.

Further reading: Measured token savings by file type · Preparing documents for RAG

Try it on your own files

Milldown converts PDFs, Office documents, web pages, and scans into clean Markdown — entirely on your computer. Free for 7 days.

Download for macOS

macOS 14+ · Apple Silicon · $39 one-time after trial (excl. VAT) · no subscription