Two correct answers, one wrong combination
“Organize” and “organise” are both correctly spelled words. So are “color” and “colour,” “center” and “centre,” “license” and “licence.” None of them is a mistake. A spellchecker set to either American or British English will happily accept whichever one matches its dictionary and reject the other — which is exactly the problem, because most spellcheckers only check one dictionary at a time, and most technical documents are never written by only one person with only one dictionary.
The actual defect isn’t either spelling. It’s using both in the same document. A reader doesn’t need to know which word belongs to which dialect to notice that something is off — mixed conventions read as unedited even to someone who couldn’t tell you the rule being broken. It’s the same category of problem as general terminology drift, just with a cause that’s easy to name once you know to look for it: contributors from different sides of the Atlantic, writing in good faith, each spelling things correctly by their own standard.
Where US and UK spelling differences come from
Most of the roughly four hundred words that differ between American and British spelling fall into a small number of patterns, which makes them easier to reason about than four hundred unrelated facts.
-ize vs. -ise. Organize/organise, recognize/recognise, customize/customise. This is the pattern most people already know about, partly because American software defaults are so widespread that the American form has become the default assumption in a lot of technical writing regardless of the author’s actual dialect.
-or vs. -our. Color/colour, favor/favour, behavior/behaviour. Notice that this one shows up constantly in software documentation specifically, because so much of it is about UI: button color, background colour, the exact word a design system names its tokens after.
-er vs. -re. Center/centre, meter/metre, theater/theatre. Less frequent in most technical writing, but a reliable tell when it does appear — a “data centre” and a “data center” are unmistakably written by people who learned different conventions.
-og vs. -ogue. Dialog/dialogue, catalog/catalogue, analog/analogue. Software has partly scrambled this one: “dialog box” is standard American UI terminology even in documents that are otherwise British throughout, since it’s often a literal API or component name, not a stylistic choice.
Beyond the patterns, there’s a smaller set of word pairs that don’t follow any rule and just have to be recognized on sight: gray/grey, tire/tyre, aluminum/aluminium, jewelry/jewellery. These trip people up more, not less, because there’s no shortcut for them — you either know the pair or you don’t.
The pairs that aren’t spelling variants at all
A few of these pairs look like spelling variants but are actually something else entirely: a genuine grammatical distinction that only exists in British English. “License” and “licence” are the clearest example. In American English, “license” is both the verb and the noun — you license software, and you hold a license to use it. In British English, “licence” is the noun and “license” is the verb — a British document can correctly say “you must license the software” and “check your licence” in the same paragraph, and that is not an inconsistency. It’s correct British grammar.
The same pattern shows up with “practice” and “practise.” Treating every instance of both spellings in a document as a dialect conflict will produce a steady stream of confident, wrong findings on exactly the documents that are most carefully and correctly written in British English. Any tool checking for this has to know which pairs are genuinely interchangeable spellings and which ones are secretly a part-of-speech distinction wearing a spelling variant’s clothes — and when it can’t tell the difference reliably, the honest answer is to leave that pair alone rather than generate false confidence.
Your document already has a convention — even if nobody chose it
Here’s the detail that makes this checkable at all: a document doesn’t need an explicit style decision to have a dominant dialect. If a document uses “organize,” “color,” and “center” nine times each and “organise” once, the document’s own body of text tells you what its convention is, whether or not anyone wrote that convention down anywhere. The single “organise” isn’t wrong in some abstract sense. It’s wrong relative to what the other 99% of the document already decided, on its own, one sentence at a time.
That’s a more useful question to ask than “which spelling is correct,” because both spellings are correct in isolation. “Which spelling matches what this specific document has already committed to” is the question that actually predicts what a careful editor would flag, and it’s the one a checker can answer without ever being told whether the intended audience is American, British, or something else entirely.
What this means for a mixed team
If your team has contributors on both sides of the Atlantic — and most distributed software teams do — the realistic goal usually isn’t “pick American or British and enforce it everywhere.” It’s noticing when a specific document has drifted away from its own established pattern, the same way you’d notice a paragraph that suddenly switched from present tense to past tense. The fix is rarely to relitigate which dialect is correct. It’s almost always to make the one document in front of you internally consistent with itself.
Check your own writing
Run a document through the terminology consistency checker to see its dominant dialect detected automatically, every minority spelling flagged against that dialect rather than against an external standard, and known part-of-speech traps like license/licence excluded rather than guessed at. For the broader question of terminology drift beyond just US and UK spelling, see terminology consistency in documentation.