SED_Tools is a Python package for downloading, standardizing, combining, and preparing stellar atmosphere spectral energy distribution libraries and photometric filter profiles for astrophysical synthetic photometry workflows. It provides unified access to multiple stellar atmosphere data sources, converts spectra and filters to consistent units and formats, builds lookup tables and flux cubes, merges separate atmosphere grids into combined libraries, and generates outputs compatible with MESA's colors module. The package includes both command-line and Python interfaces, along with tools for rebuilding and packaging spectral libraries. It also includes machine-learning components for extending incomplete SEDs and generating SEDs from stellar parameters. SED_Tools is intended to support reproducible stellar photometry, atmosphere-grid preparation, and model-observation comparison in computational astrophysics.