Users can easily import structure-related data into Chimera in the form of attributes, or values associated with atoms, residues, or models. The data can be imported with Define Attribute and then represented visually with color ranges, atomic radii, or "worm" thickness. Such data can also be manipulated programmatically in Chimera, and in fact Chimera was designed with extensibility and programmability in mind. It is largely implemented in Python, with certain features coded in C++ for efficiency. Python is an easy-to-learn interpreted language with object-oriented features. All of Chimera's functionality is accessible through Python and users can implement their own algorithms and extensions without any Chimera code changes, so any such custom extensions will continue to work across Chimera releases. Many programming examples are provided to assist extension writers.

BILD format was used in Chimera to annotate the barrel structure of green fluorescent protein with its centroid, major axis (red arrow), and an enclosing cylinder (shown with green hoops). The BILD file green.bild was generated with the python program green.py using the coordinates in green.pdb. Gallery entry courtesy of Mike Ess, Yeast Resource Center, University of Washington. (More samples...)