Onion Bandwidth Scanner (onbasca) is a Tor bandwidth scanner implementation using a database via an [Object-relationalMapping] (ORM) framework.

This project includes two main applications:

  1. A Tor relays’ bandwidth scanner (also call onbasca), which in turn is made up of the scanner and the generator:

The scanner measures the bandwidth of each relay in the Tor network (except the directory authorities) by creating a two hops circuit with the relay. It then measures the bandwidth by downloading data from a Web Server and stores the measurements.

The generator read the measurements, aggregates, filters and scales them using [Torflow]’s scaling method. Then it generates a [BandwidthFile] that is read by a directory authority to report relays’ bandwidth in its vote.

This [blog_post] also explains how Tor bandwidth scanners work.

  1. A Tor bridges’ bandwidth scanner (called onbrisca, from Onion Bridge Scanner)

The bridge scanner measures the bandwidth of obfs4 bridges in the Tor network by creating three hops circuits with the bridge as the 1st hop.

The bridges are obtained via HTTP POST requests to an endpoint. The endpoint calculates the bridges’ ratio based on the measurements and then replies to the requests are whether or not those bridges should be handled.


This software is intended to be run by researchers using a test Tor network, such as [Chutney] or [Shadow], or by the Tor bandwidth authorities on the public Tor network. Please do not run this software on the public Tor network unless you are one of the Tor bandwidth authorities, to avoid creating unnecessary traffic.


It is recommended to read this documentation at At some links won’t be properly rendered. .


See ./INSTALL.rst (in local directory or tpo Gitlab) or INSTALL.html (local build).


See ./DEPLOY.rst (in local directory or tpo Gitlab) or DEPLOY.html (local build).


More extensive documentation can be found in the ./docs directory, and online at


Copyright (c) 2020-2021, juga at riseup dot net. Copyright (c) 2022, The Tor Project, Inc.

Released under the BSD-3-Clause, which applies to all the source code and binary files except otherwise stated.

Documentation and other files are released under CC0-1.0 license.