The Jargon File (version 4.4.7, 29 Dec 2003):

toolsmith
 n.

    The software equivalent of a tool-and-die specialist; one who specializes
    in making the tools with which other programmers create applications.
    Many hackers consider this more fun than applications per se; to understand
    why, see uninteresting. Jon Bentley, in the ?Bumper-Sticker Computer
    Science? chapter of his book More Programming Pearls, quotes Dick Sites
    from DEC as saying ?I'd rather write programs to write programs than
    write programs?.


The Free On-line Dictionary of Computing (30 December 2018):

toolsmith

   The software equivalent of a tool-and-die specialist; one who
   specialises in making the tools with which other programmers
   create applications.  Many hackers consider this more fun than
   applications per se; to understand why, see uninteresting.
   Jon Bentley, in the "Bumper-Sticker Computer Science" chapter
   of his book "More Programming Pearls", quotes Dick Sites from
   DEC as saying "I'd rather write programs to write programs
   than write programs".

   [Jargon File]