"Alternative to Design by Contract is Program by Coincidence." That's why clojure/spec is huge.

In requirements work and documents, clearly differentiate between semantic invariants—core, invariable requirements and more situational or potentially changeable policies.

"Any system of agents (services) depends critically on contracts, even if they are dynamically generated." OpenAPI.

If DbC is so powerful, why isn't it used more widely?

• No good support in most languages
• Doesn't eliminate the need for testing, because blind to consistency and clerical bugs
• Benefit come from consistent use, that may feel like a drag on trivial, boilerplate parts of the code (like we are lazy to always check inputs in all code)

Well-specified interface contracts reduce cases when clients intentionally or unintentionally rely on unspecified behaviour.

Software Design Wiki

Specify interface contracts

References

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