The purpose of this study is to develop an instrument for assessing written language skills by writing descriptive texts based on local wisdom. The assessment instrument that was developed was in the form of a task that was designed to attract students to be able to speak written language through writing descriptive text. The development model used in this research is the R2D2 development model. The validation results of the validators on the six components that have been developed reached 84% of the validators stated that the assessment instrument that had been developed was feasible to be implemented in learning to write descriptions. The results of the validity and reliability tests show that each item of the task developed is valid and reliable. Besides, 88% of students' responses and impressions stated that they were very interested in the assignment that had been designed and developed in the assessment instrument. Based on the results of validation from experts, validity, reliability, and student responses, it can be concluded that the instrument for assessing the language skills of writing text descriptions based on local wisdom that has been developed is feasible to be implemented in learning to write descriptive texts.