Worked on the OPM/opm-common repository to implement declarative constraints enforcing mutual exclusivity between BRINE and SALINITY keywords at deck-load time. This approach replaced legacy runtime gating by migrating core logic from several C++ modules to parser-level validation, resulting in earlier and clearer error detection. Enhanced error handling was introduced to provide explicit feedback for invalid configurations, reducing the risk of misconfiguration and downstream failures. Expanded software testing ensured that new constraints were thoroughly validated, with updates to test suites reflecting the revised logic. The work improved maintainability and reliability of salt handling in reservoir simulations using C++ and declarative programming.