Repair Tools for Firebird
IBPhoenix offers a comprehensive collection of repair tools for Firebird and InterBase from IBSurgeon.
IBSurgeon Viewer is a free tool for investigation of internal database structure.
If you are interested in the details concerning InterBase architecture and on-disk structure, it will help you to understand the low-level work of database engine.
IBSurgeon Viewer does not use any client or server InterBase software - it works directly with low-level database structures. That is why for work with database you should have direct access to GDB/IB/FDB files.