Formulas can be entered from the command line, from GChemPaint, or directly in the formula entry.

When using the formula entry, just type a valid formula as in the following example:

After validating, if the formula has been succesfully parsed, you get:

The isotopic pattern is displayed on the second page of the notebook:

If an error occurs while parsing the formula, a message box will pop up and the cursor will be moved in the entry to the error position.