{ "background": "District hospitals in sub-Saharan Africa face persistent challenges in system reliability, affecting service delivery and patient outcomes. Existing assessment tools are often fragmented or lack a holistic operational focus, limiting their utility for guiding targeted interventions.", "purpose and objectives": "This study aimed to evaluate a novel diagnostic framework for assessing and improving hospital system reliability through a randomised field trial. The primary objective was to determine the framework's effect on a composite reliability score.", "methodology": "We conducted a parallel-group, cluster-randomised controlled trial in 24 district hospitals. Facilities were randomised to implement the diagnostic framework (intervention) or continue with routine practice (control). The framework comprised structured checklists and a facilitated root-cause analysis across five core operational domains. The primary outcome was the change in a composite reliability score (range 0-100) after 12 months. Analysis used a linear mixed-effects model: $Y{ij} = \\beta0 + \\beta1 Ti + uj + \\epsilon{ij}$, where $Y{ij}$ is the score for hospital *j* in group *i*, $Ti$ is the treatment indicator, $uj$ is the cluster random effect, and $\\epsilon{ij}$ is the residual error. Robust standard errors were estimated.", "findings": "Hospitals using the diagnostic framework showed a significantly greater improvement in mean composite reliability score compared to controls (adjusted mean difference: 8.7 points, 95% CI: 2.1 to 15.3, p=0.012). The most substantial gains were observed in the domains of medical supply logistics and maintenance systems.", "conclusion": "The structured diagnostic framework effectively identified and guided remediation of systemic weaknesses, leading to measurable improvements in overall hospital operational reliability.", "recommendations": "Health ministries should consider integrating this diagnostic framework into routine hospital management and performance review cycles. Further research should investigate its long-term sustainability and cost-effectiveness.", "key words": "health systems strengthening,