PyMGC3 is a Python toolkit to apply the Modified Great Circle Cell Counts (mGC3) method to search for tidal streams in the Galactic Halo. The code computes pole count maps using the full mGC3/nGC3/GC3 family of methods. The original GC3 method (Johnston et al., 1996) uses positional information to search for 'great-circle-cell structures'; mGC3 makes use of full 6D data and nGC3 uses positional and proper motion data.

galstreams provides a compilation of spatial information for known stellar streams and overdensities in the Milky Way and includes Python tools for visualizing them. ASCII tables are also provided for quick viewing of the stream's footprints using TOPCAT (ascl:1101.010). As of 2022, the library provides celestial, distance, proper motion and radial velocity tracks for each stream (pm/vrad when available) stored as AstroPy (ascl:1304.002) SkyCoord objects and a stream's (heliocentric) coordinate frame is realized as an AstroPy reference frame. The code offers polygon footprints and pole (at mid point) and pole tracks in the heliocentric and Galactocentric (GSR) frames. It also offers angular momentum tracks in a heliocentric reference frame at rest with respect to the Galactic center, and provides uniformly reported stream length, end points and mid-point, heliocentric and Galactocentric mid-pole, track and discovery references and information flag denoting which of the 6D attributes (sky, distance, proper motions and radial velocity) are available in the track object.