Grammar Checker

About this tool

Paste or type English text and press Check text. The checker finds spelling mistakes, words that are correctly spelled but wrong in context (such as their and they're or its and it's), agreement errors (he go, the books is), repeated words, a versus an, capitalisation and punctuation problems, and many common confusions. Each finding shows what is wrong and offers fixes; one click applies a fix to your text, and Show in text selects the passage so you can edit it yourself. Choose American, British, Australian, Canadian or Indian English so that colour, centre or realise are not flagged in the variety you use. The engine is Harper, an open-source, rule-based grammar checker written in Rust and compiled to WebAssembly, which runs entirely in your browser in a background thread: your text is not uploaded to any server, and nothing is stored. It is not an AI model and it does not rewrite your sentences. Be realistic about what it does. On a small test of 30 sentences with one planted mistake each, it flagged about 25 (our test allows 24 to 27), and on 30 correct sentences it raised no false alarm; real text will vary, so it finds many but not all problems, and a suggestion can occasionally be wrong. Read each one before you accept it, and use your own judgement for style and meaning. It checks English only; text in other languages is treated as misspelled English words. The first check downloads the engine, about 8 MB, which your browser keeps for next time. Texts up to 150,000 characters are checked; at most 600 suggestions are shown at a time, so fix the first ones and check again. Rare inputs, such as a single enormous word or right-to-left control characters, are cleaned before checking so the engine cannot crash on them.

How to use it

1. Choose your variety of English.
2. Paste or type your text and press Check text.
3. Click a suggestion to apply it, or Show in text to edit the passage yourself.
4. Check again after your changes, then copy the text.

Common problems

It flags a name or a technical term as a spelling mistake

The engine does not know every name, brand or technical word. Ignore the suggestion and leave the word as it is.

It did not find a mistake that I know is there

A rule-based checker cannot catch everything, especially mistakes that depend on meaning. Proofread the text yourself as well.

The text is in another language

Only English is supported. Other languages will be flagged as misspellings.

It says the checker could not start

The engine needs WebAssembly and a Web Worker. Use a current version of Chrome, Edge, Firefox or Safari, and check that your network allowed the first download of the engine.

Some parts could not be checked

Very unusual text can make the engine fail on that part. Split the text, remove odd symbols or very long strings of characters, and check again.