Reverse Engineering Tools
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The process for developing a tweak for jailbroken iOS can include: using a combination of class-dump, IDA, and GDB to locate functions/methods, using Cycript to prototype the tweak, and finishing it with Theos.
See Debugging on iOS 7 for using GDB/LLDB.
Logify might help you.
When working with App Store apps, you may need something like dumpdecrypted.