Editing Jet Set Willy (section)

===Third-party modifications===
In its original Spectrum version, the rooms themselves are stored in a straightforward format, with no [[data compression|compression]], making it relatively easy to create customised versions of the game.

The review of JSW in issue 4 of ''Your Spectrum'' included a section entitled "JSW — A Hacker's Guide"; remarks in this section imply that the author had successfully deduced at least some of the data structures, since he was able to remove sections of wall in the Master Bedroom.<ref name="yr04_60" /> The following year, issue 13 contained a program that added an extra room ("April Showers") to the game,<ref name="russandem"/><ref>[http://www.users.globalnet.co.uk/~jg27paw4/yr13/yr13_41.htm "April Showers"], Your Spectrum, Issue 13, April 1985</ref> and issue 15 described the data formats in detail.<ref>[http://www.users.globalnet.co.uk/~jg27paw4/yr15/yr15_33.htm "Interior Decorating"], Your Spectrum, Issue 15, June 1985</ref>

Several third-party editing tools were published between 1984 and 1986, allowing players to design their own rooms and sprites.{{citation needed|date=June 2018}}