You can use SINGULAR via the "SAGE online calculator". This can be really slow sometimes...

• First, go to https://sage.math.washington.edu:8101/ and login. You have to create an account if this is the first time you use it.
• Click "New Worksheet" to open a new document if this is the first time you use it, or open an old one.
• Find the pull-down menu which says "sage", and select "singular" instead.
• Type something in the worksheet (try 2+2; for testing...)
• Click "evaluate" to run SINGULAR on your input.