SpreadsheetFormulas

=ASSERT(formula, expected)

How we test formulas

AI formula generators hand you a formula and hope. Wrong formulas rarely announce themselves — they return numbers that look fine. So we don't ask you to trust us: every formula on this site is executed against its own sample data before it can be published, and the badge on each page tells you exactly how it was verified.

Right now: 71 of 77 pages engine-verified; the rest human-reviewed where the engine lacks the function.

  1. Structural validation

    Every page is structured data, not free text. A schema gate checks each one at build time: the formula, both platform versions, sample input, expected output, and cross-links. A page with a missing piece cannot be published — the build fails.

  2. Engine execution

    Each page carries an executable verification block: its sample data and formula are loaded into a real spreadsheet calculation engine (HyperFormula), computed, and compared against pinned expected values — with the clock frozen so date formulas like TODAY() are tested deterministically. A wrong formula, or wrong sample data, fails our test suite before it can ship.

  3. The mistakes are tested too

    Where a page warns about a common mistake — "blank due dates get flagged as overdue" — we verify both halves: that the naive formula really does misbehave, and that the guarded version really doesn't.

  4. Human review for engine gaps

    A few functions can't run headlessly (QUERY's SQL dialect, LET, and live-data features like GOOGLEFINANCE). We've extended the engine with our own tested implementations of several others it lacked — UNIQUE, RANK, TEXTBEFORE/TEXTAFTER, and the REGEX family — each covered by its own unit tests. Those pages are marked Human-reviewed: checked by hand in Excel and Google Sheets, with the review date shown on the page.

  5. You are the last test

    Every page has a feedback control. "This didn't work" reports are tracked per page, and pages that accumulate them get re-reviewed. If we shipped something wrong, we want to know — and fix it visibly.

What the badges mean

✓ Engine-verified
Computed by a spreadsheet engine against the page's sample data in our test suite, on every build.
Human-reviewed
Verified by hand in Excel and Google Sheets — used where the engine doesn't implement the function.

One honest caveat: the engine is Excel-compatible, not Excel itself. For the rare edge where engines disagree, real-spreadsheet checks win — and your reports overrule everything.