Spelling and grammar checker for Welsh

Cysill is a Welsh language spelling and grammar checker.

Cysill can, in addition to correcting spelling and general grammatical errors, correct incorrect mutation and, when errors are found, inform the user why the error is considered to be incorrect

Cysill highlights spelling errors and suggests some corrections.


Cysil finds grammatical errors and suggest the relevant correction. Grammar error messages can be displayed in Welsh or English.

Check texts in word processing applications

Cysill can be installed into popular word processing applications in Windows such as Microsoft Word and LibreOffice and accessed through convenient buttons on their toolbars.

Cysill and Cysgeir within the Microsoft Word 2016 ‘Review’ tab.
Both programs work in previous version of Microsoft Office as well as Microsoft Outlook.
Cysill and Cysgeir in LibreOffice for Windows.
Cysill and Cysgeir in Microsoft Outlook 2016

Check texts from anywhere else…

Text from nearly any program in Windows (e.g. web browser, forms application, text editor) can be sent to Cysill to be checked for any errors by

  • selecting the text
  • pressing the Ctrl, Alt and W keys.

If the original text is editable, Cysill can replace it automatically with the corrected text.

Mae’n bosib dewis bysellau brys eich hun drwy ddewis ‘Dangos -> Dewisiadau -> Bysellau Brys’ yn newislen Cysill


Cysill also includes a thesaurus which enables you to find different words that share a similar meaning, allowing you to improve your vocabulary and writing style.

Some of the synonyms Cysill suggests for ‘hapus’ (‘happy‘)