Language Assessment is still very important and needs to be continued in helping the teachers to understand their learner's performance and maintained it even though the schools are closed temporarily. This study is to explore the use of Online Formative Assessment Tools (OFAT) to ESL young learners' language performance. A descriptive mixed method design was implemented in this study to analysed the data. A set of questionnaires and three open-ended questions was distributed to 100 English teachers to two districts in Bintulu, Sarawak Malaysia. The results of the study revealed that most of the teacher agree that the use of OFAT to assess the students' performance makes teaching easier but for some extend due to some challenges such as the teacher's age, location of the schools and facilities make it difficult to be implemented in ESL classroom and prefer the traditional method instead. Further recommendation is discussed in the conclusion section regarding how to deal with the challenges of using OFAT.