INTRODUCTION: Restoration of endodontically treated teeth (ETT) is crucial for their long-term functionality, yet current practices lack structured approaches, leading to variable outcomes. The restorative difficulty evaluation system (RDES) offers a systematic method to assess restoration complexity tailored to each patient. This pilot study aims to evaluate RDES's reliability and validity in guiding clinicians' decisions on ETT restoration. METHODOLOGY: Ten participants were recruited, and two endodontists independently assessed clinical parameters using RDES. Interrater reliability was assessed to determine agreement between examiners. Test-retest reliability was evaluated over two time points (baseline and 2 weeks). Face and content validity were assessed by a panel of 10 experts. RESULTS: Intrarater reliability was robust (Evaluator 1: CONCLUSION: The study demonstrates RDES's reliability and validity in assessing restoration complexity in ETT. Its systematic approach can inform treatment decisions, potentially enhancing patient outcomes.