Online Pixel Ruler
While not a 1:1 clone of Deep Glow, there are several free utility plugins and scripts that improve the default glow:
Deep Glow After Effects: Best Free Alternatives and Workarounds
If you aren't ready to invest in the plugin yet, here is how you can get the Deep Glow look for free. 1. The "Stacking" Method (The Best Manual Workaround)
While originally part of an older preset pack, Andrew Kramer’s techniques for "Optical Glow" can be found in many free project files online.
Many creators have released free FFX preset files that automate the "stacking method" mentioned above with a single slider. 3. Using 32-Bit Linear Workspace
Deep Glow was built by independent developers. Buying the plugin ensures they can continue to update it for new versions of AE. Final Verdict
While it's tempting to look for a "free" version of —the industry-standard glow plugin by VideoCopilot/Plugin Everything—it is a premium, paid tool.