I pasted this sentence into a spell checker: “Their going to review the contract, and me and him will send the final version too the client.”
Nothing was flagged. Not one red line.
That’s the spell checker doing its job. Every word in the sentence is a real word, spelled correctly, and a plain online spell check looks at nothing else. The sentence still has three mistakes: Their should be They’re, me and him should be he and I, and too should be to.
Most people treat spell check and grammar check as one feature because they share a toolbar button. They’re two different jobs. The old advice to “run both” is also a little stale, since most grammar checkers now handle spelling in the same pass. The more useful question is what each layer can actually see, and what neither one does.
So I ran a small test. The results, including one miss I didn’t expect, are below, followed by the order I’d work in.
What an online spell check actually catches
A spell checker compares every word to a dictionary. If the word is in the dictionary, it passes. If not, you get a red line. That’s the whole mechanism, and it explains both the strength and the blind spot.
The strength is non-words: swapped letters, missing letters, the usual troublemakers like recieve, seperate and occured. The blind spot is anything that happens to be a real word. A spell checker has no idea which sentence a word sits in, so form for from and manger for manager sail through, and so does there when you meant their.
Two settings are worth checking before you trust a result. The first is the language variant: set to US English, a checker will flag colour, and after a few false alarms people start ignoring flags altogether. The second is the custom dictionary. Add client names, product names and jargon once, and they stop cluttering the results.
The test: seven mistakes, two kinds of checker
I wrote five short sentences with errors that are easy to make and easy to miss. Here they are, so you can paste them into your own tool:
Their going to review the contract, and me and him will send the final version too the client.
Please forward the invoice to there office before Friday.
The project is closer then we thought, and it's deadline moved up.
The reports, which was due on Monday, are still missing.
Recieve the seperate files before they occured twice.I ran them on October 10, 2026 through pyspellchecker 0.9.1, a plain word-list spell checker, and LanguageTool 6.8, a rule-based grammar checker. Both are open source, and both were on default settings with US English.
| Mistake | Spell check | Grammar check |
|---|---|---|
| “Their going to…” (should be They’re) | Missed | Missed |
| “me and him will send…” (should be he and I) | Missed | Missed |
| “…version too the client” (should be to) | Missed | Caught |
| “…invoice to there office” (should be their) | Missed | Missed |
| “it’s deadline” (should be its) | Missed | Caught |
| “closer then we thought” (should be than) | Missed | Caught |
| “The reports, which was due” (should be were) | Missed | Missed |
| recieve / seperate / occured | Caught 3 of 3 | Caught 3 of 3 |
The spell checker found none of the seven real-word and grammar errors. The grammar checker found three.
The first row is the one that surprised me. Their going to is the example half the articles on this topic use to show why you need a grammar check, and this grammar checker let it through. It flagged too the in the same sentence and said nothing about the rest.
Treat this as a sample, not a benchmark: one grammar checker, five sentences, no tuning. I didn’t test Grammarly, Word’s Editor or any AI-based checker, and some of them will do better. The wordcount.com grammar checker, for one, describes itself as catching homophones such as their and there. I haven’t tried it. That’s the reason the sentences are above: checking your own tool takes about a minute.
Why a clean spell check isn’t a clean document
Spell check reads one word at a time. The mistakes that make you look careless usually live between words: a wrong word that happens to be real, a missing article (Please send report by Friday), a number that’s off by a zero. An invoice for $1,500 instead of $15,000 passes every spell check ever written.
Your own head works against you as well. You wrote the sentence, so you read what you meant to say, and your eyes fill in the missing word. That’s how errors survive even a careful reread.
Here’s where I’ll commit to a view. “No red lines” tells you the words exist and nothing more. Treating it as “done” is the real mistake, a bigger one than skipping a grammar tool.
Built-in checkers sit in the same spot. Microsoft’s support page describes Editor in Word as checking spelling, grammar and style, with suggestions for tighter sentences, simpler words and a more formal tone. That’s plenty for a quick email. You can also switch individual checks off, so what a clean result means depends on what you’ve left on. For a contract, a job application or anything with money in it, a person still has to read the thing.
Do you need a separate spell checker at all? Often not. LanguageTool flagged all three misspellings above through its own spelling rule, and wordcount.com says its checker covers spelling in the same pass. A standalone spell checker still makes sense for a plain text field with nothing built in, or when you want typos flagged without a stream of style suggestions.
A workflow that doesn’t make you proofread four times
If you’re only going to run one tool, run the grammar checker. This is the order I’d use:
- Finish editing first. Cut, reorder and rewrite before any checker sees the draft. Polishing a paragraph you’re about to delete is wasted effort.
- Set the language and the dictionary. Pick US, UK or Australian English and add names and jargon, so the results aren’t padded with false flags.
- Run one grammar pass on near-final text, with spelling switched on. Accept suggestions one at a time instead of hitting “accept all”. Even wordcount.com warns that its tool sometimes proposes changes you’ll want to reject.
- Read it once more yourself, for what the tools miss. Read it aloud, change the font, or print it. Look for their/there/they’re, its/it’s, missing words, and every number and name in the piece.
- Think before pasting anything confidential. Free online spell check tools and grammar checkers handle your text differently: some process it and discard it, others keep it. Read the privacy policy before you paste a contract or a client file. If you can’t confirm what happens to your text, use a checker that runs on your own machine. LanguageTool can be run locally, for example.
Steps 2 and 3 are quick. Step 4 is where you catch what the software can’t.
So, do you need both?
You need both layers, but not two separate tools. One decent grammar checker covers the spelling pass and catches some of the real-word errors a dictionary can’t see. In my test it caught three of seven, which is why your own last read still matters.
The short version: spell check is dependable for non-words and blind to nearly everything else. Grammar check sees more, but it isn’t complete either.
Your next step takes a minute. Paste the five test sentences into whatever checker you use now, note which mistakes it lets through, and make those the things you look for by hand.
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