Recent AI-based language learning research highlights learners' crucial role, yet university learner readiness in ChatGPT-based English learning remains unexplored. Accordingly, this current research attempted to develop and validate a tool to evaluate university learner readiness for ChatGPT-assisted English learning (LRCEL) to address the research gap that the prior instruments for language learners' readiness have not taken into account the features and characteristics of ChatGPT in language teaching and learning as well as students' achievement emotions. Three hundred and forty-seven Chinese university learners participated to help explore and confirm the constructs of the LRCEL. Guided by the theory of planned behaviour and the control-value theory of achievement emotions, results of first-order and second-order confirmatory factor analysis, exploratory structural equation modelling, convergent validity and discriminant validity supported an 18-item questionnaire comprising seven dimensions. The LRCEL has been proven valid and reliable, enabling educational educators to understand university learners' readiness for ChatGPT-supported English learning with domain-specific items.