Context Based Spelling Correction is a web application that corrects the spelling errors in sentences. The current version of the system does not have grammar checking function, and the initial goal of this project was to develop a standalone spell checker. But there are other types of errors that spell checkers and grammar checkers cannot detect, such as “I love eating desert”, where “dessert” is the correct spelling for “sweet snacks” but “desert” was typed. This kind of error is called a real-word error. The main focus of this project is to looks at how a context sensitive spell checker can be built to detect real word errors by using the information probability approach. The basic framework and background necessary to develop a context-sensitive spell checker will be covered. Different approaches to context-sensitive spell checking have been investigated and the complete design and implementation of each approach will be presented