Postel's law

English

Alternative forms

• Postel's Law

Etymology

Named after Internet pioneer Jon Postel (1943–1998).

Proper noun

Postel's law

1. (software engineering) The design principle that software should be conservative as to its own behaviour (i.e. strictly compliant with specifications) but liberal in the behaviour it tolerates from other systems.
   • 2005, Jesse Liberty, Visual C# 2005: A Developer's Notebook, O'Reilly Media, →ISBN, page 47:

     Contravariance is consistent with Postel's Law: “Be liberal in what you accept, and conservative in what you send.”

Further reading

• RFC 760
• RFC 1122