Understanding packages and class files

The default formatting in LaTeX documents is determined by the class used by that document. This default look can be changed and more functionalities can be added by means of a package. The class file names have the .cls extension, the package file names have the .sty extension.

Difference between classes and packages

Sometimes it's hard to make a decision when it comes to choose whether to write a package or a class. The basic rule is that if your file contains commands that control the look of the logical structure of a special type of document, then it's a class. Otherwise, if your file adds features that are independent of the document type, i.e. can be used in books, reports, articles and so on; then it's a package.

For instance, if a company needs branded reports that use a special font and have the logo of the company in the footer; you need a new class.

If the company needs a new command that makes easier to highlight important sentences within a document, a new package will work in this scenario.

Further reading

For more information see

• Writing your own package
• Writing your own class
• LaTeX2ε for class and package writers