Tor specifications

These specifications describe how Tor works. They try to present Tor’s protocols in sufficient detail to allow the reader to implement a compatible implementation of Tor without ever having to read the Tor source code.

They were once a separate set of text files, but in late 2023 we migrated to use mdbook. We’re in the process of updating these documents to improve their quality.

This is a living document: we are always changing and improving them in order to make them easier and more accurate, and to improve the quality of the Tor protocols. They are maintained as a set of documents in a gitlab repository; you can use that repository to see their history.

Additionally, the proposals directory holds our design proposals. These include historical documents that have now been merged into the main specifications, and new proposals that are still under discussion. Of particular interrest are the FINISHED Tor proposals: They are the ones that have been implemented, but not yet merged into these documents.

Getting started

There’s a lot of material here, and it’s not always as well organized as we like. We have broken it into a few major sections.

For a table of contents, click on the menu icon to the top-left of your browser scene. You should probably start by reading the core tor protocol specification, which describes how our protocol works. After that, you should be able to jump around to the topics that interest you most. The introduction of each top-level chapter should provide an introduction.