Co-creating a program theory and evaluability assessment for an Irish single-session, synchronous chat-based youth mental health intervention: implications for outcome evaluation.

Introduction: Single-session online synchronous chat offers immediate, anonymous, single-session support for young people. However, the drop-in format attracts a diverse population with urgent and varied needs, creating challenges for evaluation. Standardized outcome measures may not capture short-term changes, and randomized controlled trials may be ethically inappropriate. These constraints point to the value of theory-based evaluation approaches rooted in implementation science, which can better capture short-term change, contextual complexity, and real-world variation in service delivery. Methods: This study applied a theory-driven evaluability assessment to Jigsaw Live Chat, an Irish single-session, synchronous chat-based mental health service for youth. A situational analysis, review of the literature, and an internal data review established the intervention context and examined existing evaluative approaches within the literature. Two co-design workshops with staff ( Results: Several contextual factors were identified as crucial to the success of Jigsaw Live Chat, including cross-collaboration, integration, and buy-in across youth mental health services. Staff defined a range of core components ( Discussion: This study presents one of the first published examples of an iterative, collaborative evaluability assessment of a single-session synchronous chat-based mental health support service. The findings clarify how such interventions operate within specific organizational and sociocultural contexts and provide the foundation for future adaptation and evaluation aimed at improving service delivery and outcomes for young people.