An element in a fetched file (a file received from the web server in response to an HTTP request) can be mapped to the source code that generated it and vice versa. When code is compiled at the web server, calls can be executed that emit HTML that includes metadata that maps a snippet of code back to a particular source file and to a particular location in the source file. The HTML can include injected symbols that specify that the information from a particular start position for a particular character length in the HTML comes from a particular start position to a particular end position in the source file.