There are two kinds of checker for your writing now. The classic spell checker compares your text with dictionaries and grammar rules. An AI spell checker sends the text to an AI model that reads it like a person, sentence by sentence. Both underline mistakes and suggest fixes, so they look alike. They are not the same, and knowing the difference helps you choose the right one.
How a rule-based spell checker works
A rule-based checker does two things. It looks up every word in a dictionary for your language and variant, and it runs the text against a large set of grammar and style rules, each written to recognize one pattern: a before a vowel sound, a plural subject with a singular verb, could of instead of could have, the same word twice in a row.
That design has clear strengths:
- It explains itself. Every mark comes from a rule, so it can say what is wrong and why, and it is grouped by kind: spelling, grammar, punctuation or style.
- It is predictable. The same text gives the same result every time, and a fix never rewrites more than the words the rule is about.
- It is fast and cheap to run. That is why it can check long texts in one go and be free to use.
Its limit is the other side of the same design: it only knows the patterns someone wrote a rule for. A word that is spelled correctly but is the wrong word, such as We will meet form 9 to 11, passes the dictionary. A sentence can follow every rule and still be hard to read.
How an AI spell checker works
An AI spell checker reads whole sentences and suggests corrections in context. Instead of matching patterns, the model judges what the sentence is trying to say and what a careful writer would have written. That lets it catch what rules miss:
- real words in the wrong place: form for from, loose for lose, manger for manager
- a missing word, as in Please let know if you have questions
- sentences that are grammatical but clumsy, or that sound translated
- tense and agreement mistakes that only show up across a long sentence
It has weaknesses of its own. A model can change more than it needs to, smoothing a sentence you wrote that way on purpose. It can be wrong while sounding certain, and the same text may not get exactly the same suggestions twice. It also takes far more computing power than a rule check, which is why the AI Spell Checker & Grammar Checker limits free use.
Rule-based vs AI spell checker: side by side
| Spell checker | AI spell checker | |
|---|---|---|
| How it checks | Dictionaries and grammar rules | An AI model that reads whole sentences |
| Best at | Typos, agreement, punctuation, confused pairs like its and it's | Wrong words that are spelled right, missing words, clumsy sentences |
| Explanations | One per mark, by kind of mistake | Corrections in context |
| Same text, same result | Yes | Not always |
| Free use | Free, no account needed | Limited, because it costs more to run |
When to use a spell checker or an AI spell checker
Use the rule-based spell checker for
- everyday emails, messages and posts, where you want the typos gone in seconds
- long documents, up to 150,000 characters in one check
- texts in a specific variant, such as British or Canadian English, or in one of more than 30 languages
- situations where you want to see and decide on every single change yourself
Use the AI spell checker for
- texts that matter: an application, a cover letter, a report for a client, anything published
- writing in a language that is not your first, where the mistakes are often correct words in the wrong place
- a paragraph that passed the spell checker but still reads awkwardly
Or use both spell checkers in this order
For an important text, run the Online Spell Checker first and fix the clear mistakes. Then give the text to the AI Spell Checker & Grammar Checker. With the typos already gone, its suggestions are about what is left: the wrong word, the missing word, the sentence that needs a different shape. You spend the limited AI checks where they help most, and you review a short list instead of a long one.
You stay in control with either spell checker
Neither kind of checker knows your text as well as you do. Before you accept a suggestion, read the sentence it produces. Be especially careful with:
- names, numbers, dates and prices, which a checker cannot verify
- quotations, which keep their original wording
- technical, legal or medical terms, where a more common word is not a better one
- your own voice: a suggestion that makes a sentence more correct but less like you is optional
For the mistakes a rule-based check is built to catch, with an example of each, see Ten common grammar mistakes a grammar checker finds.
Spell checker privacy and data protection
Both checks run online: your text is sent from your browser to be checked, and the AI spell checker passes it to an AI model. Your personal dictionary is kept in your browser, not in an account; its words go along with a check only so that the checker leaves them alone. A few habits keep you on the safe side with any online writing app:
- Do not paste passwords, account numbers or other secrets into any checker.
- For a confidential text, check whether you are allowed to share it with an online service at all, for example under a contract or your employer's rules.
- Where the details do not matter for the check, replace names and personal data with placeholders before you paste.
What happens to the text you check is described in our privacy policy.