Modern web applications are growing in complexity and becoming more widely used. Using frameworks to build APIs is a popular way for both hobby developers and businesses to speed up development time and save costs. With this dependence on frameworks to be the foundation for potentially large applications comes the need to understand their performance qualities and which areas they are best suited for. This study compares the performance of the two similarly popular frameworks ASP.NET Core and Express.js, when used together with a MySQL Database to build Web APIs. This was done by building two different API implementations in each framework, one employing a RESTful approach and the other using the new querying language GraphQL. Experiments were run where the peak CPU usage, peak memory usage and response times were measured.The results of the experiments were that in a RESTful API, ASP.NET Core is faster at serving requests during lower loads whereas Express.js outperforms ASP.NET Core when faced with a higher amount of concurrent requests that fetch a lot of data. In a GraphQL API Express.js was able to perform similarly or better in all cases in terms of response times and resource usage compared to ASP.NET Core.