Proxomitron, the Universal Web Filter, is a filtering web proxy written by Scott R. Lemmon. This program was originally designed to run under Windows 95.
All future development of the program was ceased in 2003 with its author's death; even so, Proxomitron is still viable and used on modern Windows platforms such as XP and Vista.
Properly configured, Proxomitron intercepts HTTP traffic between the user's browser and web servers. The program is capable of altering web page content by removing or adding text. Additionally, it can add, modify, or delete HTTP message headers, be configured to block connections or redirect requests based on the web page address, and be configured to route connections through a remote proxy. The user can monitor connections and filter activations, if desired.
Program operation is dictated through the use of a configuration file containing specialized filters which can be written, edited, deleted, enabled or disabled by the user via the program's graphical user interface. (Third-party filters can also be imported, or "merged," into the configuration.) The filters utilize a "matching" language similar to the standard regular expressions used in text editing. Additional files, such as "blocklists" and SSL DLLs, can extend filtering capabilities.