Postel's law
Source status: Source not yet verified by the archive.
Be conservative in what you send and liberal in what you accept.
In context
This law belongs with Murphy's Laws, where small assumptions, timing, and system complexity tend to turn into memorable failures.
Editorial note
The robustness principle encouraged tolerant receivers, but modern protocol guidance also warns that accepting malformed input can create ambiguity and security risk.
Practical example: An API documents strict input validation while preserving backward compatibility only for explicitly supported older fields.
Reviewed ยท RFC 1122
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