Regex Tester & Validator

Matches Wikimedia Commons/Wikipedia thumbnail image URLs, which follow the pattern /thumb/<hex-char>/<2-hex-chars>/<filename>/<width>px-<filename>, where directories are sharded by the file's MD5 hash prefix. It captures the base thumbnail path and the original image filename (jpg, jpeg, png, or gif), and requires the resized copy after the pixel-width prefix (e.g. 220px-) to exactly match the original filename via a backreference. With global, multiline, and case-insensitive flags, it can extract multiple thumbnail links per text block regardless of extension casing. Useful for validating, parsing, or recovering original filenames from Wikipedia thumbnail URLs.