Architecture

Robustness Principle

Be conservative in what you send, be liberal in what you accept.

Also known as Postel's Law (after Jon Postel, author of the TCP specification), this principle guided the design of internet protocols.

In Modern Software

API endpoints should accept flexible input formats but return strict, well-defined output
Parsers should be tolerant of minor formatting errors
UI forms should accept various date formats but store them in ISO 8601

Controversy

Some argue this leads to ambiguity and interoperability issues over time, as producers rely on consumers being liberal.

Resources

Wikipedia

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