Five spot checks before you trust a spreadsheet an assistant built

A spreadsheet comes back with tidy columns, a neat total and not a single error cell. It looks finished. That is exactly when it is worth five minutes, because a spreadsheet can be wrong in ways that do not look wrong: a total that skips a row, a column in the wrong units, a formula quietly replaced by a typed-in number.

These checks need no special tools. They work whichever way the sheet was made, by a colleague, a script or an AI assistant, and they take one pass through it. Think of them as acceptance tests for work that is not code. The examples below are illustrative.

Check 1: Recompute one total by hand

Pick one total and rebuild it a second way, with a calculator or a quick filter and sum. Choose one that matters, not one that is easy: the grand total, or the figure that will be quoted in a meeting. If it matches, you have tested the formula and the data it points at in one go. If it does not, stop there and find out why before you look at anything else.

Check 2: Count the rows

Compare the number of rows in the result with the number of items in the source. A summary of 212 rows built from a source of 220 has lost eight, and you want to know which eight and why. Look at the last row too: ranges that end one row early are a classic. Do the same for columns: does every column you asked for exist, and does each one have the same number of filled cells?

Check 3: Read the units and the dates

Look at one value in each column and ask what it is measured in. Dollars or thousands of dollars? Hours or minutes? Then read the dates as dates: is 03/04 the third of April or the fourth of March? A mismatch that is invisible in one cell shows up fast in a sorted column.

Check 4: Click into the formulas

Click into five cells of a calculated column, including the first and the last. Do they all hold the same formula? A single typed-in number in the middle of a column of formulas is easy to miss and expensive when the source changes. If your spreadsheet program can show formulas instead of values, use that view: inconsistent cells stand out at a glance.

Check 5: Try one edge case

Change one input to something extreme: zero, a blank, a very large number, a negative one. Watch what the totals do. A division error, or a total that does not move at all, tells you how the sheet will behave in real use. Then undo your change.

A hypothetical example

An assistant builds a monthly expenses sheet. Check 2 shows 118 rows against 120 expenses in the source. The missing two turn out to be refunds, recorded as negative amounts and dropped by a rule nobody mentioned. The total was neat and wrong. One line in the brief (“include refunds, shown as negatives”) means next month’s sheet starts right.

Put the checks in the brief

Next time, build the five checks into the task itself: ask for the row count against the source, the units of each column and a note of any rule that excluded items. The helper does the first pass, and you do the spot check on top. Over a few months, the list of things you catch becomes the checklist you hand over.

Where Octuo fits

We’re the Octuo team. Octuo is a personal assistant and one starting point for work across AI, tools and specialist services. It operates external solutions on your behalf, and you grant its permissions: on first launch macOS asks for Screen Recording and Accessibility, which is what lets Octuo see the screen and act on your behalf, under your control. It reports back when a job is done. Octuo is available for macOS.