Minecraft Packet Analyzer Proxy is a regular TCP proxy with a packet parser for Minecraft: Java Edition (1.14.4). It is currently a WIP.
The parser is being made with the information present in wiki page.
This was built with a similiar structure to the proxy made by LiveOverflow for the game PwnAdventure3. If you want a detailed explanation of how this works you should see his video.
For now, I don't have the sufficient knowledge to implement protocol encryption support, this means the proxy can only be used in servers in offline mode.
For more information about protocol encryption, check the wiki page.