Visualizations in teaching have become a common practice as they effectively convey theoretical concepts. Compiler construction, a heavily theory-based subject in computer science education, is particularly challenging for students to understand. While many tools simulate a compiler’s front end, or analysis phase, applications that focus on the back end, or synthesis phase, are scarce. This paper describes textsc{VisOpt}, a web-based visualization tool designed for a master’s level Compiler Construction course. VisOpt focuses on the synthesis phase, i.e., code optimization and code generation. Its primary objective is to help students comprehend various local compiler optimizations, which can be visualized on the original code, an intermediate representation, or an assembler-like target code. A quasi-experiment with a pre-test-post-test design revealed that students who used VisOpt reported higher self-efficacy compared to those who did not. Although no significant improvement in learning outcomes was observed overall, we propose VisOpt as an engaging pedagogical tool that effectively complements traditional methods for teaching the synthesis phase of compilers.