The KS Level Composer program is being developed to help level authors track down those nasty wallswims and to ease level designing.
-- Placing the updates here below ---
Current version: 0.3.16 (2009_10_01)
Current version can:
+ check for wallswims (naive check used, possible false-positives)
+ edit level using almost the same logic as Nifflas' original editor (still in development, but the basics are there)
+ select multiple tiles in tileset and paste them all at once
+ duplicate several rooms all together with their object metadata, with or without adjusting shifts / warps
+ list powerups and keys
+ follow shifts and warps directly in editor
The releases are stored at
http://xoft.cz/games/kslc.html not to clutter this thread.
The program doesn't need any installation, just download and unpack (possibly the zlib1.dll as well, if you dont have one already) and run.
At the first run it should ask you for the KS executable (so that it knows the path to all KS data folders). If it doesn't (strange) or you set the wrong path, you can change it later in Settings (menu View -> Settings...)
If it still gives you trouble, please write the contents of the Log tab.