basis1

Find the plugs before you trust someone else's model

A plug is a number someone typed over a formula to make the model behave. It looks like every other cell. Basis is a spreadsheet that recomputes every formula in a workbook, compares the result against the values Excel itself cached in the file, and hands you what it finds — plugs, broken references, circular dependencies and stale links, each with coordinates.

Audit a workbookUse the parsing API

Free, no account needed. Your workbook is processed and discarded — it is never stored. Reads .xlsx and .xlsm.

What real workbooks contain

Measured across two public corpora — the Enron spreadsheets and FUSE, 4,207 formula-bearing workbooks between them. Figures are for substantial models, those carrying at least a thousand formulas. How we measured this →

  • 43.2%

    carry a hardcoded plug

    A constant typed over a formula in an otherwise-uniform fill-down. Found by comparing bytecode program identity, so an overtyped cell is a structural discontinuity — not a guess.

  • 22.6%

    have a broken reference

    #REF! left behind by a deleted row, column or sheet, along with every dependent that quietly inherited the error.

  • 41.1%

    link to a workbook you don't have

    External links whose values were cached the last time someone with the other file opened this one.

Checked against Excel, not trusted

Every .xlsx carries the values Excel computed the last time it was saved, which makes each file its own test case. We recompute all of them and report what disagrees — by coordinate, rather than rounded away.

97.31%

of 3,344 Excel-written workbooks recompute cell-for-cell with zero divergence — 4,033,846 formulas compared. Method and limitations →

What we had to get right

Matching Excel means matching its edge cases, not its documentation. Each of these cost us a bug, a regression test and a corpus scan — so we wrote them down. If you are debugging one of them right now, the answer is here and you do not need us for it.

All verified Excel semantics →