The increasing demand for transparency and accountability in sustainability practices has heightened the importance of high-quality Environmental, Social, and Governance (ESG) reporting. However, assessing the quality of ESG disclosures remains a challenge due to their predominantly qualitative nature and varying reporting practices. This study addresses this gap by developing ESG quality indices to assess the quality of ESG reporting through nine key dimensions: environmental position, environmental development, environmental performance, social position, social development, social performance, social performance, social performance, social performance, governance position, governance development, governance performance. These dimensions are then refined to 22 items. Using 15 ESG reports from listed companies at Hong Kong Stock Exchange in 2024, this study conducted pre-testing of the instrument using the Content Validity Index (CVI), inter-rater reliability (Krippendorff’s alpha), and internal consistency (Cronbach’s alpha). The results indicate that the instrument is a valid and reliable tool for assessing the quality of ESG reports. This study offers both methodological and practical contributions. Methodologically, it presents a replicable tool that enhances rigor in ESG reporting assessments. Practically, it provides stakeholders, such as regulators, investors, and standard setters with a structured approach for benchmarking ESG disclosures, ultimately supporting improved transparency, comparability, and accountability in sustainability reporting. The ESG quality index development contributes to quality assessment of ESG information disclosure, making the qualitative item operationally measurable.