Rega is used to determine the regioselectivity for C-H functionalisation reactions, currently focusing on the sulfinate-mediated functionalisation reactions popularised by Phil Baran's group.
The program can calculate regioselectivity for either a single compound at a time or a list of compounds. Details on how to use these modes are listed below:

Single Compound:

When calculating a single compound, the user can either enter a SMILES string for their given compound directly in the box or they can draw the compound they wish to calculate in the molecule editor. One the user has finished drawing the compound in the editor, click the Transfer/Update SMILES and the SMILES string will be pasted in the box.
Enter the name of your compound then choose from the drop-down list which functional group you would like to add, either CF₃, CF₂H or ⁱPr. Once each of these boxes has been filled out press submit and your compound will be calculated.

Multiple Compounds:

For multiple compounds to be calculated at once, they need to be submitted as a .csv file. The file needs to have the following format:
The first column contains the compound name, the second contains the SMILES string and the third contains the functional group you want to add.
Click the upload file button on the page and select the .csv file with your compounds. Then click submit and your compounds will be calculated.

Results page:

The results page displays an image of the calculated compound with the possible sites of reaction labelled as numbers. The results table alongside this image details the predicted regioisomeric ratio of the compound. The Activation energy and ratio numbers are displayed and can be interpreted as follows:
If site 1 has a ratio value of 4 and site 2 has a ratio value of one, then that tells the user they can expect a 4:1 ratio of product with substitution occuring at site 1 vs site 2.

Login and Accounts:

While Rega can be used without creating an account, it is recommended. An account allows the user to view their previously calculated compounds and the data generated for them.