Luhn Validator

The tool implements the Luhn checksum algorithm to verify numbers commonly used in payment processing and identity validation. It is intended for developers, data engineers, QA specialists, and payments teams who need reliable, repeatable validation of numeric identifiers before they enter gateway systems or analytic pipelines. The focus is on accuracy, determinism, and predictable behavior across input formats. By design, the tool operates fully offline, with no external calls, making it suitable for sensitive environments and batch jobs where data privacy and throughput matter. Inputs are sanitized by removing non-digit characters, leaving a pure digit string. The algorithm enforces typical length constraints (12 to 19 digits for most card schemes) before performing the checksum. The Luhn calculation proceeds from the right: every second digit is doubled; if the result is greater than 9, nine is subtracted; all digits are summed. A final sum divisible by 10 indicates validity. The tool can also report a best-effort card_type when requested, based on number length patterns, without implying issuer authentication. Outputs are deterministic and structured: is_valid (boolean), normalized_number (string of digits), digits_count (integer), and optional card_type. Error handling covers empty input, non-numeric strings after sanitization, and lengths outside 12–19 digits. Assumptions include numeric input with optional separators; exclusions include live issuer lookups, transaction processing, or any sensitive data storage. Use cases include real-time form validation, data cleansing, and pre-submission checks for payment workflows.