This information is stored in the
blend files header, so you can find out without having to load Blender at all.
This has the advantage you can scan a directory of 100's (or 1000's) of blend files in a very short time (a few seconds even if the files are large).
Blender comes with a script in
scripts/modules/blend_render_info.py which can extract this data from a blend file (you don't even need Blender to be installed just a copy of this file and Python is enough).
You can load the script as a module or execute it directly.
command line example:
# python blend_render_info.py /path/to/my_test.blend
1 250 Scene
This can run inside blender,
blend_render_info.py will have to be in Python's
filepath = "/path/to/my_test.blend"
frame_start, frame_end, scene = blend_render_info.read_blend_rend_chunk(filepath)
print("total frames:", (frame_end - frame_start) + 1)
As you can see the frame range and active scene is stored, if you want more info you'll have to use a script and load the file into Blender.