The control group will receive basic psychoeducation. The content of the psychoeducation is very similar to the content of session 2 of the STARS chatbot and includes psychoeducation about emotions, a personal story about a fictional character who talks about her emotions, and information about where to access mental health support. It also includes a list of organizations and clinics providing mental health care in Lithuania.

Changes in symptoms of adjustment disorder are measured. The Brief Adjustment Disorder Measure-8 (ADNM-8, Kazlauskas et al., 2018) is a self-report measure comprising 8 items about symptoms of adjustment disorder. All items are answered on a 4-point Likert scale that ranges from 1 (never) to 4 (often). A higher score indicates more pronounced symptoms. In the Lithuanian sample, the ADNM-8 had a good internal consistency with Cronbach's α of 0.93 (Kazlauskas et al., 2023).

Changes in suicidal ideation are measured. The SIDAS (Van Spijker et al., 2014) is a self-report measure comprising 5 questions about suicidal ideation. All items are answered on a 10-point Likert scale that ranges from 0 (never, no control, not close at all, not at all) to 10 (always, full control, made an attempt, extremely). A higher score indicates more pronounced symptoms. In the Lithuanian sample, the SIDAS had a good internal consistency with Cronbach's α of 0.93 (Skruibis et al., 2022).

Changes in functioning are measured. The WHODAS 2.0 (Ustun et al., 2010) is a self-report measure comprising 12 questions about functioning. All items are answered on a 5-point Likert scale that ranges from 0 (none) to 4 (extreme or cannot do). A higher score indicates more pronounced symptoms. Previous studies have shown good psychometric properties of the WHODAS 2.0 (Cronbach α = 0.96) (Saltychev et al., 2021).

Changes in psychological well-being are measured. The World Health Organization Well-being Index-5 (WHO-5, Bech, 2004) is a self-report measure comprising 5 items about psychological well-being. All items are answered on a 5-point Likert scale that ranges from 0 (at no time) to 4 (all of the time). A higher score indicates more pronounced psychological well-being. In the Lithuanian sample, the WHO-5 had a good internal consistency with Cronbach's α of 0.87 (Nomeikaite et al., 2023).

Changes in internalized stigma of psychological difficulties (the term of psychological difficulties instead of mental illness is used in this study) are measured. The Internalized Stigma of Mental Illness-Brief Version (ISMI-10, Boyd et al., 2014) is a self-report measure comprising 10 items about internalized stigma of psychological difficulties. All items are answered on a 4-point Likert scale that ranges from 1 (strongly disagree) to 4 (strongly agree). A higher score indicates more pronounced internalized stigma of psychological difficulties. Previous studies have shown good psychometric properties of the ISMI-10 (Cronbach's α = .75-.81) (Boyd et al., 2014).

Changes in stigma of self-stigma of seeking help are measured. The Self-Stigma of Seeking Help-Ultra-Brief Version (SSOSH-3, Brenner et al., 2021) is a self-report measure comprising 3 items about self-stigma of seeking help. All items are answered on a 5-point Likert scale that ranges from 1 (strongly disagree) to 5 (strongly agree). A higher score indicates more pronounced self-stigma of seeking help. Previous studies have shown good psychometric properties of the SSOSH-3 (Cronbach's α = .82-.87) (Brenner et al., 2021).

Changes in client service are measured. The Client Services Receipt Inventory (CSRI, Beeacham and Knapp, 2001) is a self-report measure comprising questions about client service. The CSRI covers a broad range of services that may be utilized, including primary and secondary care services, other services, and informal care.

Changes in health are measured. The EQ-5D-5L (EuroQol Research Foundation, 2019) is a self-report measure comprising 5 items about health. All items are answered on a 5-point Likert scale that ranges from 1 (I have no problems or similar) to 5 (I am unable or similar). A higher score indicates more pronounced symptoms. Convergent validity was demonstrated by a correlation between EQ-5D-5L and the WHO-5, (r = .43, P < .001) (Janssen et al. 2013).

Symptoms of post-traumatic stress disorders before intervention are measured. International Trauma Questionnaire (ITQ, Cloitre et al., 2018) is a self-report measure comprising 18 items. All items are answered on a 5-point Likert scale that ranges from 0 (not at all) to 4 (extremely). A higher score indicates more pronounced symptoms. ITQ will be used as a predictor in the analysis. In the Lithuanian sample, the ITQ had a good internal consistency with Cronbach's α of 0.86 (Dumarkaite et al., 2023).

Resilience before intervention is measured. The Resilience scale (RS-14, Wagnild, 2011) is a self-report measure comprising 14 items about resilience. All items are answered on a 7-point Likert scale that ranges from 1 (strongly disagree) to 7 (strongly agree). A higher score indicates more pronounced resilience. RS-14 will be used as a predictor in the analysis. The analysis of the psychometric properties of the RS-14 in the sample of Lithuanian adolescents demonstrated high reliability of the scale (Zelviene, 2020).

The usability of the intervention is measured. Participants are asked to evaluate the usability of the intervention by indicating how useful (from 1 "not useful at all" to 5 "very useful"), satisfactory (from 1 "I did not like it at all" to 5 "I liked it a lot"), easy to use (from 1 "it was not easy at all" to 5 "it was very easy"), etc., the program is. Participants are also asked to report their subjective impression regarding the improvement of mental well-being (from 1 "worsened a lot" to 5 "improved a lot"), physical health (from 1 "worsened a lot" to 5 "improved a lot"), general understanding of oneself and one's well-being (from 1 "not at all" to 5 "definitely improved"), recommending the program to others (from 1 "not at all" to 5 "definitely would recommend"), etc.