Background The presence of a tongue-tie (ankyloglossia) in an infant may lead to breastfeeding difficulties, but debate continues about which babies should be treated with frenotomy. The Bristol Tongue Assessment Tool (BTAT), a clear and simple evaluation of the severity of tongue-tie, is being used worldwide and translated into different languages. We aimed to produce a simple picture version of the BTAT to aid and enhance consistent assessment of infants with tongue-tie. Methods The Tongue-tie and Breastfed Babies (TABBY) assessment tool was developed from the BTAT by a graphic designer, with iterative discussion with four practicing NHS midwives. The TABBY tool consists of 12 images demonstrating appearance of the infant tongue, its attachment to the gum and the limits of tongue mobility. The TABBY tool is scored from 0 to a maximum of 8. Two initial audits of the TABBY were undertaken at a large maternity unit in a secondary care NHS Trust, in Bristol UK from 2017 to 2019. TABBY was evaluated by five midwives on 262 babies with tongue-ties and experiencing breastfeeding difficulties who were referred for assessment to a tongue-tie assessment clinic using both BTAT and TABBY. Each pair of scores was recorded by one midwife at a time. A further training audit with 37 babies involved different assessors using BTAT and TABBY on each baby. Results All midwives found the TABBY easy to use, and both audits showed 97.7% agreement between the scores. We suggest that a score of 8 indicates normal tongue function; 6 or 7 is considered as borderline and 5 or below suggests an impairment of tongue function. Selection of infants for frenotomy required an additional breastfeeding assessment, but all infants with a score of 4 or less in the audits had a frenotomy, following parental consent. Conclusions The TABBY Assessment Tool is a simple addition to the assessment of tongue-tie in infants and can provide an objective score of tongue-tie severity. Together with a structured breastfeeding assessment it can inform selection of infants for frenotomy. It can be used by clinical staff following a short training and will facilitate translation into other languages.