In a previous pilot study, a digital self-guided intervention for insomnia showed preliminary positive effects on insomnia symptoms. In order to optimize the digital self-guided format, this study will evaluate the added value of three treatment features on treatment engagement and insomnia symptoms. The participants will be adults with insomnia. The trial will be a 2x2x2 randomized factorial experiment, where the following features/factors will be manipulated: an optimized graphical user interface (yes or no), an adaptive treatment strategy (yes or no), and daily prompts to use the intervention (yes or no). The factorial experiment will create 8 equally large groups (1:1:1:1:1:1:1:1), who will receive the different combinations of features. The main outcome will be the effect on treatment engagement.

Inclusion Criteria:

1. ≥ 18 years of age.
2. ≥ 15 points on Insomnia Severity Index.
3. Insomnia diagnosis, according to criteria in the Diagnostic and Statistical Manual of mental disorders-5 (somatic/psychiatric comorbidity is allowed).
4. Good understanding of the Swedish language.
5. No practical obstacles to participate in treatment and assessments.
6. Daily access to computer/smart-phone/tablet with Internet access.
7. Can receive phone calls and text messages during the study period.

Exclusion Criteria:

1. Sleep diseases, such as narcolepsy or sleep apnea.
2. Somatic or psychiatric illnesses that either are directly contraindicated for the treatment, require other treatment, or entail symptoms/a functional level making it too difficult to participate in the study.
3. Alcohol/drug abuse, or medication with side effects on sleep (however, sleep medication is allowed).
4. Working nights or night shifts.

IPD available anonymized on reasonable request.

Participants will be blinded to what condition they are randomized to, and will not receive information concerning what features are being manipulated in the experiment.