Specctra DSN format — KiCad's export for handoff to external auto-routers like Freerouting. Plain text S-expression. Contains components, layers, nets, and design rules.
How it looks
Illustration: DSN text written for this card with CORE3588 values
What a DSN file looks like inside, cut down to a few lines. The values are CORE3588's: 0.2 mm track width and clearance (written in microns, 200), R60's position, and the real three-pad net Net-(Q1-B) (highlighted). Written by hand for this card, because KiCad's command line cannot export DSN; the KiCad window does that.
How it works
Where it fits
The DSN is the question; the SES file is the answer. Freerouting reads one and writes the other.
Both are text in the same nested-bracket style as KiCad's own files (s-expression), so a script can read and check them.