API designPrinciple

Postel’s Law

Send carefully formed messages, and be tolerant of what you receive.

A plain-language paraphrase. Original sources below.

The idea behind it

The robustness principle appears in early Internet protocol specifications. Tolerating variation can aid interoperability, but silently accepting malformed input can also create ambiguity and hide defects. Apply it with care: modern protocol guidance warns that tolerance can make an ecosystem harder to evolve.

Go to the source

RFC 793, section 2.10 — Robustness Principle
RFC 9413 — Maintaining Robust Protocols

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