Front-ends may lack representation for some of KeyValue's basic types: number, text, boolean and date. In that case lexical conversions are required. For instance, LibreOffice Calc and Excel do not have specific representations for time. Instead, they use a double which represents the number of days since a certain epoch. Therefore, the front-end must convert from double to KeyValue's representation of time.

Moreover, lexical conversions can make user interface more friendly. For instance, LibreOffice Calc and Excel users might prefer to use "Yes" and "No" rather than the built-in boolean values TRUE and FALSE.

Front-ends must implement all lexical converters they need. The lexical conversion cited above (from text to boolean values) is, indeed, implemented for LibreOffice and Excel add-ins. Instead of TRUE and FALSE we can use any of the following strings:

Additionally, LibreOffice and Excel add-ins implement lexical conversions from text to number, that is, providing the text "1.23" when a number is required is the same as providing the number 1.23.