FriendlyReader and TeCST are text simplification tools developed at Linköping University, using an API service at the university called SAPIS. Both tools are web services that run in the browser for users. To improve the services an implementation of state-transition tracking was chosen as a way to both improve the website by enabling the user to undo actions, but also enable the client to cache information which lowers the amount of requests required to SAPIS. Two libraries, called MobX and Redux, where compared to find the one which worked best for FriendlyReader and TeCST. The main difference between MobX and Redux is the programming paradigms, MobX is object-oriented while Redux is functional. In the end MobX was chosen due to the object-oriented nature of the library which is more familiar for beginners while also requiring less code to achieve similar results. MobX lacks native support to keep track of previous state transitions which is required to be able to go back to a previous state. Using MobX a new library called GlobalStore was created to solve this problem. An implementation example for synonyms was produced as a proof of concept for FriendlyReader.