Systems and methods for performing dynamic code management, such as dynamic management of JavaScript tags in webpages or code segments in native applications, are disclosed. A user device loading a web or native application can access a factor, such as a user device-specific attribute or a piece of content of the webpage or native application being loaded. That factor can be applied to a rule that is evaluated (e.g., by the user device or a code server) to select one or more desired segments of code (e.g., JavaScript tags or native application code) to be executed by the user device from a pool of available code (e.g., pre-embedded code or dynamically injected code).