OBJECTIVE: To explore healthcare professionals' (HCPs) experiences of diagnosing cellulitis, identify unmet diagnostic needs and determine the desirable characteristics of an ideal diagnostic test. DESIGN: Qualitative study using semistructured interviews, analysed thematically. SETTING: Community and secondary care services across the UK from January 2023 to September 2023. PARTICIPANTS: 25 UK-based HCPs (eg. nurses, paramedics, pharmacists, general practitioners and hospital physicians) with recent experience of managing cellulitis. Inclusion required recent involvement in cellulitis care; no specific exclusion criteria were applied. All participants completed the interview. RESULTS: Four major themes were identified. Theme 1 described patient and disease characteristics that make diagnosis difficult, including atypical or recurrent presentations, high-risk patients, pre-existing wounds or ulcers, darker skin tones and prior antibiotic use, which represented specific use cases in which a test could be deployed. Theme 2 highlighted clinician and patient behaviours contributing to misdiagnosis, including reliance on cellulitis as the 'default' diagnosis, limited dermatology/tissue viability knowledge and access, risks of not treating and patient expectations. Theme 3 examined candidate diagnostic aids (evaluated in early studies) and ideas for novel diagnostic tools, noting that current tools are insufficiently specific, while enthusiasm for new technologies was countered by concerns about usability, comfort, infection control and training needs. Theme 4 identified key characteristics of an ideal test: portable, rapid, equitable, usable across community and hospital settings and providing a probabilistic result rather than a binary outcome. CONCLUSIONS: Cellulitis remains diagnostically challenging across multiple care settings. Developing tools that can distinguish patients who genuinely require antibiotic therapy from those with non-infective inflammation would be particularly valuable. The greatest potential for impact lies in improving diagnostic specificity to reduce misdiagnosis, unnecessary antibiotic use and avoidable healthcare attendance and admission. Broad engagement of stakeholders will be essential to define acceptable performance parameters and guide novel technology development.