This evaluation evaluated Health Education England's NoObesity digital health app's usability and acceptability to undertake activities improving families' diet, physical activity and weight. The purpose of the study is to evaluate the app's influence on self-efficacy and goal setting and to determine what can be learned to improve its design for future studies, should there be evidence of adoption and sustainability.

Inclusion Criteria:

• adult users (over 18 years)
• fluent in English
• willing to use the app
• parents or legal guardians of a child or children OR health care professionals linked to the parent or guardian
• owner of a smartphone to access the app, with 4G data access

Exclusion Criteria:

• individuals who are known to the researchers or staff at Health Education England
• deaf or hearing impairment
• prior use of the app before study commencement
• refusal to give informed consent
• children, vulnerable young people, or vulnerable adults.