"You aren't gonna need it" (YAGNI) is a principle which arose from

extreme programming Extreme programming (XP) is a software development methodology intended to improve software quality and responsiveness to changing customer requirements. As a type of agile software development,"Human Centred Technology Workshop 2006 ", 2006, ...

(XP) that states a

programmer A programmer, computer programmer or coder is an author of computer source code someone with skill in computer programming. The professional titles Software development, ''software developer'' and Software engineering, ''software engineer' ...

should not add functionality until deemed necessary. Other forms of the phrase include "You aren't going to need it" (YAGTNI) and "You ain't gonna need it".

Ron Jeffries Ron Jeffries (born December 26, 1939) is one of the three founders of the Extreme Programming (XP) software development methodology In software engineering, a software development process or software development life cycle (SDLC) is a proc ...

, a co-founder of XP, explained the philosophy: "Always implement things when you actually need them, never when you just foresee that you

ill ILL, or Ill, or ill may refer to: Places * Ill (France), a river in Alsace, France, tributary of the Rhine * Ill (Vorarlberg), a river in Vorarlberg, Austria, tributary of the Rhine * Ill (Saarland), a river of Saarland, Germany, tributary o ...

need them."

John Carmack John D. Carmack II (born August 21, 1970) is an American computer programmer and video game developer. He co-founded the video game company id Software and was the lead programmer of its 1990s games ''Commander Keen'', ''Wolfenstein 3D'', ''Do ...

wrote "It is hard for less experienced developers to appreciate how rarely architecting for future requirements / applications turns out net-positive."

Context

YAGNI is a principle behind the XP practice of "do the simplest thing that could possibly work" (DTSTTCPW). It is meant to be used in combination with several other practices, such as continuous

refactoring In computer programming and software design, code refactoring is the process of restructuring existing source code—changing the '' factoring''—without changing its external behavior. Refactoring is intended to improve the design, structure, ...

, continuous automated

unit testing Unit testing, component or module testing, is a form of software testing by which isolated source code is tested to validate expected behavior. Unit testing describes tests that are run at the unit-level to contrast testing at the Integration ...

, and

continuous integration Continuous integration (CI) is the practice of integrating source code changes frequently and ensuring that the integrated codebase is in a workable state. Typically, developers Merge (version control), merge changes to an Branching (revisio ...

. Used without continuous refactoring, it could lead to disorganized code and massive rework, known as

technical debt In software development and other information technology fields, technical debt (also known as design debt or code debt) refers to the implied cost of additional work in the future resulting from choosing an expedient solution over a more robust o ...

. YAGNI's dependency on supporting practices is part of the original definition of XP.

References

{{Reflist, 30em, refs= ''Extreme Programming Installed'', Jeffries, Ronald E.; Ann Anderson, Chet Hendrickson (2001). 265 pages, p. 190, webpage:
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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." ''Extreme Programming examined'', Succi, Giancarlo; Michele Marchesi, 2001, 569 pages, webpage:
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quote: "XP says 'do the simplest thing that could possibly work ' because 'you aren't gonna need it'." {{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 ''Object-oriented & classical software engineering'', Schach, Stephen R. (2007). 618 pages, p., webpage:
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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)." {{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 Fowler, Martin;

Kent Beck Kent Beck (born 1961) is an American software engineer and the creator of extreme programming, a software development methodology that eschews rigid formal specification for a collaborative and iterative design process. Beck was one of the 17 o ...

(8 July 1999). ''Refactoring: Improving the Design of Existing Code''. Addison-Wesley Professional, 431 pages, p. 68, webpage:
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{{ISBN, 978-0201485677. Quote: "you aren't going to need it". Poppendieck, Mary; Tom Poppendieck (2003). ''Lean Software Development: An Agile Toolkit'', p.59, webpage:
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Quote: "

, ''Extreme Programming Explained'', Chapter 17, uses the acronym YAGNI (You Aren't Going to Need It) for this practice and explains its rationale." Olsen, Russ (2007). ''Design Patterns in Ruby'', p.13, webpage:

{{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)." Programming principles Extreme programming English phrases

Context

See also

References