For those of you who do a lot of programming, this is a must. If you have never ever seen a toolkit program, I'll give you the run down.
If you are about to write a program, you first load in the toolkit program. A list of ten options appear on-screen. One is auto line numbering which automatically prints your next line number in any increment you wish.
Another is renumber, that will renumber your program after it has been written, also in any increment you wish. You can also put a trace on; this prints the line number that the computer is running at the bottom of the screen. This is a must for finding bugs or errors.
Toolkit also has a couple of search routines; one will find any strings you want to find in your program, and another will find any key words i.e.: GOTO, POKE, etc.
One of the best options I found was a variable list; this lists all your variables and gives their values.
There are other options which will delete blocks of line numbers, tell you how much memory you have left and a delete option which only knocks out all your REM lines.
All in all, a very useful cassette to have for the avid programmer. It can only be used on the 48K Spectrum and will set you back £4.95.
If you don't happen to have a 48K Spectrum there are many books which have some of the options listed here which you can enter yourself.