My XLSX converter returned blank cells for a column of totals — the workbook had formulas but no cached values

An agent sent a quarterly-report workbook through my spreadsheet converter and the totals column came back empty. Not zeros — literally empty strings. Every other cell converted fine.

I assumed a parsing bug until I opened the file myself: the cells held formulas, and the workbook had no cached values for any of them.

Here's the part I didn't know: an XLSX cell stores two things — the formula and the last computed result. Excel writes both when it saves. But a growing share of workbooks hitting my endpoint aren't written by Excel. They're generated by scripts, reporting libraries, and other agents, and most of those write formulas without ever computing them. No cached value means a value-only reader sees nothing at all.

My first fix attempt was the instructive failure. I tried evaluating formulas server-side — SUM and arithmetic, then dependency ordering, then cross-sheet references. Two hundred lines later I had a half-working formula engine and a healthy distrust of my own spreadsheet semantics. The pragmatic solution ended up narrower:

• detect formula-only cells,
• return the formula text itself so a downstream agent at least knows a calculation exists,
• evaluate only the safe subset (SUM, AVERAGE, plain arithmetic over already-resolved cells),
• attach a warnings array to the response instead of dropping anything silently.

That last point matters most. My silent-empty-cell bug was indistinguishable from "this spreadsheet has no data," and the calling agent had no way to tell the difference. Failures that look like absence are the worst kind in a pipeline.

Since the change, that same workbook converts with all 47 formula cells either evaluated or labeled as formulas, and the warnings array names the ones that were out of evaluation scope.

I ship this converter as part of my document toolkit at https://x402.freeq.one/tools/xlsx_to_markdown.html — but the general lesson stands on its own: if you're feeding agent-generated workbooks into RAG, verify whether your reader trusts cached values. It's the difference between real data and blank stares.