How to Catch the Mistakes Spellcheck Misses

Read the notice below once, at normal speed, and count the mistakes. It has 29. We ran it through two spellcheckers with two dictionaries each. Hunspell flagged 7 of the errors and Aspell 8. The other 21 passed all four runs, because each one produces a real word and a spellchecker only asks whether a word is real. What finds those 21 is a short list of searches and one slow read aloud.

We wrote the notice for this test. It is 155 words long and nobody sent it to anyone. It is unfair to the spellchecker, and I meant it to be: 21 of the 29 errors are real words on purpose. Those are the errors that reach your reader, because they are the ones a red underline never shows you.

What four dictionaries flagged

The checkers were Hunspell 1.7.2 (the spellchecker in LibreOffice, Firefox and Chrome) and Aspell 0.60.8.1, each with its American (en_US) and British (en_GB) dictionary. Each was asked to list the words it did not recognise.
Hunspell listed eight words with each dictionary: seven errors and one false alarm, 6pm. Aspell listed eight with each, all of them errors. The misspellings recieve, untill, definately and seperate and the lower-case london are on all four lists.
The commands were hunspell -d en_US -l and aspell list -l en_US, and the same with en_GB. The notice mixes British and American spelling in two places (organisers with recognized, colour with color). We counted each mix as one error and as caught when a dictionary flagged either half.

Hunspell’s American dictionary accepted lower-case english; the other three rejected it. Hunspell’s British dictionary accepted both organisers and recognized, so it never noticed that mix. And where a variety word was flagged, it was flagged as a plain misspelling. Nothing in the output says “this text mixes two varieties”, so a writer who doesn’t know which dictionary is loaded can easily correct the wrong half.

The 29 errors by kind, with how many at least one run caught:

• Wrong sound-alike (12 planted, none caught): you’re, principle, its, effects, loose, there, passed, to, lead, Their, it’s, bored
• One-letter slip that makes a real word (4 planted, none caught): form, quite, casual, then
• Misspelling (4 planted, all caught): recieve, untill, definately, seperate
• Agreement (2 planted, none caught): several people has; these meeting is
• Lower-case proper noun (2 planted, both caught): london (all four runs), english (three of four)
• British and American mixed (2 planted, both caught): organisers / recognized; colour / color
• Doubled word (1 planted, none caught): the the
• “Would of” (1 planted, none caught): would of told you
• Rare real word in the wrong place (1 planted, none caught): refractory (for refectory)

The full answer key (29 errors)

you’re (your), recieve (receive), the the (the), principle (principal), form (from), untill (until), would of (would have), definately (definitely), quite (quiet), several people has (have), its (it’s), effects (affects), loose (lose), there (their), passed (past), seperate (separate), london (London), to (too), casual (causal), organisers with recognized (one variety), colour with color (one variety), refractory (refectory), english (English), lead (led), then (than), Their (There), these meeting (this meeting), it’s (its), bored (board).

The 21 that passed every run are the ones that change what the notice says. A spellchecker looks each word up and moves on. Form is in the dictionary, so “closed form Monday” passes. People, has, these and meeting are all good words; the mistake is in how they sit together, and a lookup doesn’t see that. We did not test the grammar checkers built into Word or Google Docs, so this page makes no claim about what they would catch. We did run the same notice through LanguageTool afterwards, and that is written up in A Grammar Checker Caught 19 of Our 29 Planted Mistakes.

A checker for the words spellcheck passes

This checker does the searching part of the method below. Paste your text, or press “Try the example” to run it on the first three sentences of the notice.

It marks “would of” and its relatives and any word typed twice in a row (red), 68 sound-alike words such as their, its, to and then (yellow), and 24 words that are one letter away from another word, such as form and quite (blue). It does not know which word is wrong. It highlights every their and every to, right or wrong, so that you look at each one: run on the whole notice it makes 23 highlights, of which 18 are real errors and 5 are words used correctly. It knows nothing about grammar, so it misses “several people has”, “these meeting is” and refractory, and it doesn’t check spelling at all. Use it after your spellchecker and before you read aloud.

First, spellcheck in both varieties

Set the document language to British or American English, run the spellchecker and fix every flag. Then switch to the other variety and run it again. The new flags are the words spelled the other way: in our test the American dictionaries flagged organisers and colour, and the British ones flagged color. Decide which variety the document is in and make the rest match. British and American spelling differences covers which spellings belong to which.

While you’re there, look at every name yourself. One of our four runs let lower-case english through.

Then search for the words you read past

Your eye reads the word you meant, so don’t rely on reading for these. Open Find (Ctrl+F, or Cmd+F on a Mac), choose “whole words” if the option is there, and type each word in the list. At every hit, apply the test beside it. The checker above marks every word in the list for you.

• their, there, they’re: “belonging to them” / “in that place” / “they are”
• its, it’s: if “it is” or “it has” fits, it’s; otherwise its
• your, you’re: if “you are” fits, you’re
• to, too: too means also or more than enough
• then, than: than compares; then is about time or what follows
• lose, loose: loose rhymes with goose and describes a fit or a knot
• affect, effect: affect is nearly always the verb, effect the noun
• principle, principal: a principle is a rule; principal means main, or the head of a school
• passed, past: passed is the verb; walk past, in the past
• lead, led: led is the past tense
• form, from: search for the one you did not mean
• quite, quiet: quiet is silence; quite is a degree
• casual, causal: causal is cause and effect; casual is relaxed
• bored, board: a board is a plank or a committee
• accept, except: accept is to receive; except is apart from
• whose, who’s: if “who is” or “who has” fits, who’s
• weather, whether: whether introduces a choice
• advice, advise: advise is the verb; advice is the noun

Add your own. If people keep correcting ensure and insure in your writing, that pair goes on your list.

Two more searches belong here. Search for “could of”, “would of”, “should of”, “must of” and “might of”, and change each of to have. Then search for doubled words. If your editor’s Find accepts regular expressions, the pattern \b(\w+) \1\b finds them all at once; run on the notice, it returned “the the” and nothing else.

Then read it aloud

Three kinds of error can’t be searched for, because there is no wrong word to type into the box. The notice has the first two.

1. Agreement. Go sentence by sentence, find the verb and ask who or what is doing it. Watch for plural nouns that don’t end in s (people, children) and for this or these in front of a noun of the wrong number.
2. Rare words. If you seldom use a word, look it up before it goes out. Refractory means stubborn, or resistant to heat. A refectory is a dining hall. Both are spelled correctly, so nothing flags the swap.
3. Missing and extra words. Read the whole text aloud, slowly. If your computer can read it to you, better still, because it reads what is there and not what you meant.

Reading aloud comes last because it is weakest on sound-alikes. “Their will be a meeting” sounds fine.

Four sentences from the notice, fixed

Before: The principle hall will be closed form Monday untill Friday.

After: The principal hall will be closed from Monday until Friday.

What found it: Spellcheck: untill. Search: principle (“the rule hall” doesn’t fit), form.

Before: We would of told you sooner.

After: We would have told you sooner.

What found it: Search: would of.

Before: Several people has complained about noise; its a real problem and it effects everyone.

After: Several people have complained about noise; it’s a real problem and it affects everyone.

What found it: Agreement: who complained? People, so have. Search: its (“it is” fits), effects (it’s the verb here).

Before: Lunch will be served in the refractory.

After: Lunch will be served in the refectory.

What found it: Looking up the rare word. Nothing else.

The whole method fits on one page, with a tick box beside each step: download the proofreading checklist (PDF).

Corrected on 7 October 2026: this page said three kinds of error in the test notice cannot be searched for. The notice has two of them, agreement errors and a rare word in the wrong place. Missing and extra words are general advice and were not part of the test.