I've used this a few times, and while it is good for alerting you of passive voice as well as a few other things, as far as these kinds of apps go I prefer Grammarly, and would suggest it to others as my top pick for grammatical assistance.
Comparison of the angles of insertion for intramuscular (IM), subcutaneous, and intradermal injections. An IM injection is given at a 72- to 90-degree angle. A subcutaneous injection is usually given at a 45-degree angle, but may be given at up to a 90-degree angle, if a short needle is used or if the person is heavy. The intradermal injection is given holding the syringe nearly parallel to the skin (10- to 15-degree angle).