Internet-delivered Strengths Use Intervention

Work engagement will be measured with the Utrecht Work Engagement Scale (UWES-9). It has 9 items that form three dimensions, each with 3 items: vigor (e.g., "At my work, I feel bursting with energy"), dedication (e.g., "I am enthusiastic about my job"), and absorption (e.g., "I am immersed in my work"). This measure uses a 7-point agreement scale (0 = never, 6 = always).

Psychological capital will be measured with the 12-item Psychological Capital Questionnaire. It has four subscales: hope ("At the moment, I feel quite fulfilled at work."), self-efficacy ("I feel confident presenting information to a group of colleagues."), resilience ("Usually, at work, I easily get over the stressful aspects."), and optimism ("I am optimistic about what will happen to me in the future regarding my job."). All 12-item are reported on a 6-point Likert scale (1 = strongly disagree, 6 = strongly agree).

Strengths use will be measured with a set of six items, rated on a 0 (almost never) to 6 (almost always) Likert scale. A sample item is "I seek opportunities to do my work in a manner that best suits my strong points".

Burnout will be assessed with the 12-item Burnout Assessment Tool (BAT). This questionnaire has four subscales: exhaustion (3 items; "At work, I feel mentally exhausted."), emotional impairment (3 items; "At work, I feel unable to control my emotions."), cognitive impairment (3 items; "At work, I have trouble staying focused.") and mental distance (3 items; "I struggle to find any enthusiasm for my work."). All items will be scored on a 5-point scale ranging from 1 (never) to 5 (always).

Job satisfaction will be measured with the Michigan Organizational Assessment Questionnaire. The scale has three items with a response on a 7-point scale (1 = total disagreement, 7 = total agreement). A sample item reads: "In general, I like working here.".

Job performance will be assessed with a 7-item scale. Response options range on a Likert scale from 1 (strongly disagree) to 5 (strongly agree). A sample item is "I adequately complete my assigned duties.".

Positive Affect (PA) will be measured with the 10 items of the Positive Affect Negative Affect Schedule (PANAS), representing different types of positive emotions (e.g., "excited", "inspired", and "enthusiastic"). Respondents will be asked to indicate to what extent they experienced these in the time frame of the intervention on a 5-point scale (1 = very slightly or not at all; 5 = very much).

Life satisfaction will be measured with the five items of the Satisfaction with Life Scale. All answers are reported on a 7-point Likert scale (1 = totally disagree; 7 = totally agree); one item example being, "I am satisfied with my life".

Employability will be measured with the four-item Perceived Employability Scale. Each item is rated on a 5-point liker scale (1 = totally disagree; 5 = totally agree). Higher scores represent higher levels of employability.

Satisfaction with the intervention will be measured using 22 items. We will use 6 items aiming at the program's content retrieved from a questionnaire used for measuring the alliance between trainers and trainees. The minimum score is 6 and the highest is 42. A higher score means a better outcome (increased satisfaction with the intervention). Also, we will use 16 items retrieved from a scale previously used for measuring the satisfaction with an online intervention. Nine of the items are measured on a Likert scale. The minimum score is 7 and the maximum is 42. A higher score means greater satisfaction. 7 items are open-ended questions.

We will use a 10-item questionnaire designed to measure participants' satisfaction with the online platform used for the program delivery. The total score of the System Usability Scale ranges between 0 and 100. A higher score means a better outcome.

The number of completed assignments; Quality of completed assignment (qualitative rating of the degree of completeness and depth of the answer for each assignment, conducted by two independent experts based on apriori established coding grids).