This single-center, two-phase cohort study aimed to develop and validate a simple endoscopic classification of fundoplication integrity after anti-reflux surgery (ARS - Nissen or Toupet fundoplication). Consecutive adult patients undergoing endoscopy, high-resolution manometry (HRM), and reflux monitoring after ARS were included. Retroflexed endoscopic videoclips were reviewed blinded to clinical and functional results. In the development cohort (2018-2024, n=73), individual endoscopic parameters were tested against pathologic GERD (Lyon 2.0 criteria). Three parameters significantly correlated with pathologic reflux: (1) intrathoracic valve location, (2) disrupted valve (deep anterior and/or posterior grooves), and (3) visible hiatal opening. Patients were stratified according to the number of impaired mechanisms (0-3). Symptom burden, manometric abnormalities, and reflux metrics worsened progressively with increasing impairment. The rate of pathologic GERD rose from 11.8% (0 mechanisms) to 37.5% (1-2 mechanisms) to 85.7% (3 mechanisms). The classification was then prospectively validated in an independent cohort (2024-2026, n=49), reproducing the same stepwise correlation. The number of impaired mechanisms showed excellent discriminatory capacity for pathologic GERD (AUC 0.860 in development, 0.870 in validation; overall AUC 0.869). This simple endoscopic classification, based on only three objective parameters, reliably identifies fundoplication failure and correlates with symptoms and objective pathophysiologic data. It has the potential to standardize endoscopic reporting after ARS.