Commonly Confused Words Checker
Paste your writing and the checker highlights every word that belongs to one of 47 commonly confused groups — their / there / they’re, affect / effect, its / it’s, then / than and more — and lists the rule that separates each group. It cannot tell which word you meant, so it marks candidates to verify rather than errors. Free, no sign-up, and nothing is uploaded.
How to Use the Commonly Confused Words Checker
- Paste your text. The scan runs as you type, in your browser only.
- Read the counts. Total words, flagged words (every occurrence of any listed word) and the number of different groups involved.
- Check every highlight against its card. Each card names the group found in your text and gives a one-line rule, such as its = possessive; it’s = it is or it has. Decide for each occurrence whether you chose the right member.
- Fix by hand. The tool does not change your text. Edit your draft, then paste it again if you want to confirm the right words are in place.
What It Does and Does Not Do
The checker is a review list, not an error detector. It matches 98 words from 47 groups — 43 pairs and 4 triples (their/there/they’re, to/too/two, cite/site/sight, ensure/insure/assure) — in any capitalisation, with straight or curly apostrophes. Every occurrence of a listed word is highlighted whether it is right or wrong, so common words such as to, then and past will always light up. It does not look at the sentence, so it cannot say their should be there, and it does not match other forms of a word: affects and affected, lying and laid, or principals are not found.
If you want errors flagged by their context — should of, more then, its a — the Grammar Checker looks for those specific patterns. This page is for the broader job: walking through every place where a mix-up was possible.
Five Groups That Cause Most of the Trouble
| Group | Rule | Quick test |
|---|---|---|
| its / it’s | its is possessive; it’s is it is or it has | Say it is in its place. If the sentence still works, use it’s. |
| their / there / they’re | their belongs to them; there is a place or a placeholder subject; they’re is they are | Say they are. If it fits, use they’re. If the word shows ownership, use their. |
| affect / effect | affect is usually the verb (to influence); effect is usually the noun (the result) | Try influence for a verb, result for a noun. |
| then / than | then is time or sequence; than is comparison | If you can say more, less, rather before it, use than. |
| fewer / less | fewer for things you count; less for amounts | Fewer errors, less time. |
Exceptions exist. Effect is a verb in to effect change (to bring about), and in psychology affect is a noun meaning an observable emotional expression. Both are standard in those fields; use them only when you mean them.
Confusions That Matter in Research Writing
- cite / site / sight. You cite a source, visit a site, and take in a sight. “Site your sources” is the classic slip.
- imply / infer. An author implies something; the reader infers it. A paper that “infers” a result is claiming to deduce it.
- principal / principle. Principal investigator, principal component, but principle of parsimony.
- complement / compliment. A method complements another; a reviewer compliments your work.
- passed / past. The deadline has passed; in the past.
Worked Example
The 19-word line below gives 10 flagged words from 8 groups. Only two are wrong; the checker marks all ten, and you do the judging:
Text
Their going to affect the principal’s decision, and its effect is bigger then expected. The weather is quiet, to.
Flagged (10)
Their, to, affect, principal, its, effect, then, weather, quiet, to
Verify
Their going should be They’re going; bigger then should be bigger than; its effect is correct; affect the decision is correct; principal’s decision is correct if you mean a school head or main person.
The final sentence shows the limit: The weather is quiet, to. is highlighted for weather, quiet and to, but the checker never says that the last to should be too.
Which Tool Do You Need?
| If you want to… | Use |
|---|---|
| Walk through every confusable word with its rule | This Commonly Confused Words Checker |
| Flag specific mistakes by pattern — should of, more then, its a | Grammar Checker |
| Find words that are not in a dictionary | Spell Checker |
| Look up every word that sounds the same as one word | Homophone Finder |
| Fix capital letters on sentence starts, I and proper nouns | Capitalization Checker |
Frequently Asked Questions
- What are commonly confused words?
- They are words that look or sound alike but differ in meaning or use: their / there / they’re, affect / effect, its / it’s, then / than. Spell-checkers cannot catch them, because each member is a real word.
- How does the checker work?
- It highlights every occurrence of any of 98 words from 47 groups, and shows the usage rule for each group it found. It does not analyse the sentence, so it cannot say which word you should have used.
- Why is a correct word highlighted?
- Because the tool flags every listed word, right or wrong. The aim is to make you verify each one. Common words like to and then will therefore always be marked.
- What is the difference between affect and effect?
- Use affect as a verb meaning to influence (The delay affected the results) and effect as a noun meaning a result (The delay had an effect on the results). Rare exceptions: effect as a verb (to effect change) and affect as a noun in psychology.
- Does the tool find all forms of these words?
- No. It matches the exact words on its list. Affected, effects, laid, lying and principals are not matched, so check inflected forms yourself.
- How is this different from the Grammar Checker?
- The Grammar Checker flags a few high-confidence mistakes by their pattern, such as should of or more then. This tool flags all uses of a much larger set of words, right or wrong, and leaves you to judge each.
- Is my text uploaded?
- No. The scan runs entirely in your browser.