Design of electronic filters is a tool that allows the calculation of the most common filter configurations from passive filters to some concepts of digital filters.
You can calculate the operating frequency of low pass filters , high pass , band rejection with RC , RL and RCL .

The tool has a feature that allows saving calculations on a draft locally , can be shared by email or message.

It also has a tool to generate graphs , allowing to estimate the behavior of a filter with different ranges.