Word.ws English Dictionary

Postel's law

Postel's law proper noun: 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.

Proper noun

Postel's law

  1. 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.
    • Contravariance is consistent with Postel's Law: “Be liberal in what you accept, and conservative in what you send.”2005, Jesse Liberty, Visual C# 2005: A Developer's Notebook, O'Reilly Media, →ISBN, page 47

Forms of Postel's law

alternative formPostel's Law

Origin of Postel's law

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

Questions about Postel's law

What does Postel's law mean?
Postel's law means 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.
What part of speech is Postel's law?
Postel's law is a proper noun.

Words near Postel's law in the dictionary

  1. postees
  2. postehaste
  3. postejaculatory
  4. postejection
  5. Postel
  6. Postel's law
  7. postelection
  8. postelectoral
  9. postelectronic
  10. postelectrophoretic
  11. postelectroporation

Source and license

Adapted from Wiktionary: Postel's law (page history and authors). Text available under the Creative Commons Attribution-ShareAlike 4.0 license. Word.ws reformatted the entry and added links. Wiktionary data of 2026-09-02.

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