This is the source repository for the GROWTH Target of Opportunity Marshal, or ToO Marshal for short. It is a platform that has been developed by the Global Relay of Observatories Watching Transients Happen (GROWTH) collaboration in order to coordinate follow-up observations of multimessenger transients. The ToO Marshal's responsibilities include:

1. Ingest alerts for astrophysical multimessenger transients from LIGO/Virgo, IceCube, Fermi, Swift, and other experiments.

2. Notify on-duty GROWTH astronomers when multimessenger transients occur that meet triggering criteria for science programs.

3. Plan optimal observations for a heterogeneous network of ground-based telescopes including ZTF, DECam, KPED, Gattini, and GROWTH-India.

4. Submit observations to robotic telescope queues and monitor the progress of observations.

5. Provide a central interface for vetting candidates from these facilities in combination with external data sources including the Census of the Local Universe (CLU) galaxy catalog.

6. Automatically compose GCN Circular astronomical bulletins.

At its core, the ToO Marshal is powered by two open-source Python packages: ligo.skymap for processing and manipulating gravitational-wave localizations, and gwemopt for multi-facility optimal tiling and observation scheduling.

Architecturally, the ToO Marshal is a Flask web application backed by a PostgreSQL database and using a Celery asynchronous task queue for supervising long-running background operations.