The processing of server pages is emulated at run time. The system includes a library of custom tags, and a server page emulator for reading the server page, including identifying any calls to the library of custom tags, and further for emulating any calls to the custom tags identified in the server page; and thereby generating and processing the server pages dynamically at runtime. Each server page is parsed to create a tree of nodes for each element of the page, and each node identified as one of template text, custom tag start, custom tag end, and expression language (EL) expression. For each template text node, text is written directly to final markup. For each custom tag node, a return code indicates that the body should be skipped, processed normally, or provided as bulk data to the tag implementation. For each EL expression node, the EL expression is evaluated and the result written to final markup.