Worked on the gchq/CyberChef repository to enhance the reliability of the XOR Checksum operation by implementing robust input validation. Focused on back end development using JavaScript, the work introduced a check to ensure the blocksize parameter is always a positive integer. This approach prevented potential runtime errors and reduced the likelihood of edge-case failures during data processing. By strengthening error handling and input validation, the update improved the maintainability and resilience of the codebase. The change contributed to a more stable user experience and reflected a commitment to defensive programming practices within the existing workflow for checksum calculations.