Non-deterministic smart contracts are blockchain programs whose outcomes can vary even when given the same inputs. Unlike deterministic contracts, which always produce identical results under the same conditions, non-deterministic contracts depend on external data sources or unpredictable factors. This makes their behaviour less consistent and harder to verify across all nodes in a distributed network.

In most blockchain systems, determinism is essential because every node must reach the same result to maintain consensus. Non-deterministic elements, such as real-world data, timestamps, random number generation, or API inputs, can introduce inconsistencies if not handled properly. To manage this, developers often use trusted data providers known as oracles. These oracles feed external information into the contract in a controlled and standardised way, helping reduce discrepancies.

Examples of non-deterministic smart contracts include those used in insurance, betting platforms, and financial derivatives, where outcomes depend on real-world events like weather conditions, sports results, or market prices. Since these inputs are not generated within the blockchain, they introduce uncertainty.

While non-deterministic smart contracts expand the practical use cases of blockchain technology, they also come with risks. These include reliance on external data sources, potential manipulation of inputs, and challenges in maintaining network consensus. As a result, developers must design such contracts carefully, often combining off-chain computation and verification mechanisms to ensure reliability, accuracy, and security in decentralised applications.