I'm planning to launch a small side-money-maker SaaS based on my work experience (basically utilizing the knowledge and make a by-product). Two major fields I'm thinking of, one is a REST API Tester, the second is a PEP8 Python code quality checker (integrated with CI/build etc).

The former has bigger market I think but there's more competition, the latter is more exotic and maybe a bit unique (or can be, nice status report etc), but seems less "useful".

Would be good to see some feedback and thoughts, so that I can make a decision! Thanks.