Editing You aren't gonna need it

{{short description|Software engineering principle}}
"'''You aren't gonna need it'''"<ref name=XPi/><ref name=XPe/> ('''YAGNI''')<ref name=OOC/> is a principle which arose from [[extreme programming]] (XP) that states a [[programmer]] should not add functionality until deemed necessary.<ref name=XPA/> Other forms of the phrase include "You aren't going to need it" (YAGTNI) <ref name=Ref/><ref name=LSD/> and "You ain't gonna need it".<ref name=DPiR/>

[[Ron Jeffries]], a co-founder of XP, explained the philosophy: "Always implement things when you actually need them, never when you just foresee that you [will] need them."<ref name=RJef/> [[John Carmack]] wrote "It is hard for less experienced developers to appreciate how rarely architecting for future requirements / applications turns out net-positive."<ref name="Carmack">{{cite tweet |last=Carmack |first=John |author-link=John Carmack |user=ID_AA_Carmack |number=1405932642005041153 |date=18 June 2021 |title=It is hard for less experienced developers to appreciate how rarely architecting for future requirements / applications turns out net-positive. https://t.co/lusGdzkfd3 |language=en |access-date=2 December 2022 |archive-url=https://web.archive.org/web/20220816030942/https://twitter.com/ID_AA_Carmack/status/1405932642005041153 |archive-date=16 August 2022 |url-status=live}}</ref>

==Context==
YAGNI is a principle behind the XP practice of "do the simplest thing that could possibly work" (DTSTTCPW).<ref name=XPe/><ref name=OOC/> It is meant to be used in combination with several other practices, such as continuous [[Code refactoring|refactoring]], continuous automated [[unit testing]], and [[continuous integration]]. Used without continuous refactoring, it could lead to disorganized code and massive rework, known as [[technical debt]].{{Citation needed|date=February 2020|reason=Reliable source needed for the whole sentence}} YAGNI's dependency on supporting practices is part of the original definition of XP.

==See also==
{{Portal|Engineering}}
<!-- Please keep entries in alphabetical order & add a short description [[WP:SEEALSO]] --> 
{{div col|colwidth=20em|small=yes}} 
* [[Don't repeat yourself]]
* [[Feature creep]]
* [[If it ain't broke, don't fix it]]
* [[KISS principle]]
* [[Minimum viable product]]
* [[MoSCoW method]]
* [[Muntzing]] 
* [[Overengineering]]
* [[Premature optimization]]
* [[Single-responsibility principle]]
* [[SOLID]]
* [[Unix philosophy]]
* [[Worse is better]]
{{div col end}} 
<!-- please keep entries in alphabetical order -->

== References ==
{{Reflist|30em|refs=
<ref name="XPi">
   ''Extreme Programming Installed'', [[Ronald E. Jeffries|Jeffries, Ronald E.]]; Ann
   Anderson, Chet Hendrickson (2001). 265 pages, p. 190, webpage:
   [https://books.google.com/books?id=l4zO3OWkdIsC&pg=PA190&dq=%22you+aren't+gonna+need+it%22&hl=en Books-Google-dIsC], quote:
   "YAGNI: 'You Aren't Gonna Need It.' This slogan, one of XP's
   most famous..., reminds us always to work on the story we have,
   not something we think we're going to need."
</ref>
<ref name="XPe">
   ''Extreme Programming examined'', Succi, Giancarlo; Michele Marchesi, 2001, 569 pages, webpage:
   [https://books.google.com/books?id=VSChTNjn_O0C&q=%22you+aren't+gonna+need+it%22 Books-Google-VSCh], quote:
   "XP says 'do the simplest thing that could possibly work&nbsp;'
   because 'you aren't gonna need it'."
</ref>
<ref name="XPA">
{{cite book
  |editor1=Lindstrom, Lowell |editor2=Carmen Zannier |editor3=Erdogmus, Hakan 
  | title =Extreme Programming and Agile Methods – XP/Agile Universe 2004: 4th Conference on Extreme Programming and Agile Methods
  | series=Lecture Notes in Computer Science | publisher=Springer
  | location=Berlin |year=2004 |page=121 |isbn=3-540-22839-X}}
</ref>
<ref name="OOC">
   ''Object-oriented & classical software engineering'', Schach, Stephen R. (2007). 618 pages, p., webpage:
   [https://books.google.com/books?id=hWwhAQAAIAAJ&q=%22you+aren't+gonna+need+it%22 Book-Google-hWwh], quote:
   "Two acronyms now associated with extreme programming are YAGNI
   (you aren't gonna need it) and DTSTTCPW (do the simplest
   thing that could possibly work)."
</ref>
<ref name="RJef">
{{cite web
  | url=http://ronjeffries.com/xprog/articles/practices/pracnotneed/
  | title=  You're NOT gonna need it!
  | access-date=2007-11-07|date=April 4, 1998
  | author=Jeffries, Ron }}
</ref>
<ref name="Ref">
   [[Martin Fowler (software engineer)|Fowler, Martin]]; [[Kent Beck]] (8 July 1999).
   ''Refactoring: Improving the Design of Existing Code''.
   Addison-Wesley Professional, 431 pages, p. 68, webpage:
   [https://books.google.com/books?id=1MsETFPD3I0C&pg=PA68 BGoogle-1M].
   {{ISBN|978-0201485677}}. Quote:
   "you aren't going to need it".
</ref>
<ref name="LSD">
   Poppendieck, Mary; Tom Poppendieck (2003).
   ''Lean Software Development: An Agile Toolkit'', p.59, webpage:
   [https://books.google.com/books?id=hQk4S7asBi4C&pg=PA59 BGoogle-hQ].
   Quote: "[[Kent Beck]], ''Extreme Programming Explained'', Chapter
   17, uses the acronym YAGNI (You Aren't Going to Need It) for this
   practice and explains its rationale."
</ref>
<ref name="DPiR">
   Olsen, Russ (2007).
   ''Design Patterns in Ruby'', p.13, webpage:
   [http://www.informit.com/store/design-patterns-in-ruby-9780321490452].
   {{ISBN|9780321490452}}.
   Quote: "This design principle comes out of the Extreme Programming
world and is elegantly summed up by the phrase You Ain't Gonna Need It (YAGNI
for short)."
</ref>
}}

[[Category:Programming principles]]
[[Category:Extreme programming]]
[[Category:English phrases]]