LibSBML is an application programming interface library for reading, writing, manipulating and validating content expressed in the Systems Biology Markup Language (SBML) format. It is written in ISO C and C++, provides language bindings for Common Lisp, Java, Python, Perl, MATLAB and Octave, and includes many features that facilitate adoption and use of both SBML and the library. Developers can embed libSBML in their applications, saving themselves the work of implementing their own SBML parsing, manipulation and validation software. Where python-libsbml holds all officially accepted SBML Level 3 extensions, python-libsbml-experimental additionally also contains extensions that are not officially ratified yet. That means that changes to the object structure and API are possible.