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A '''Web cache''' (or '''HTTP cache''') is a system for optimizing the World Wide Web. It is implemented both client-side and server-side. The caching of multimedia and other files can result in less overall delay when [[web browser|browsing]] the Web.<ref>{{Cite web |last=Fountis |first=Yorgos |date=4 May 2017 |title=How does the browser cache work? |url=https://pressidium.com/blog/2017/browser-cache-work/}}</ref><ref>{{Cite journal |last1=Messaoud |first1=S. |last2=Youssef |first2=H. |date=2009 |title=An analytical model for the performance evaluation of stack-based Web cache replacement algorithms |url=https://onlinelibrary.wiley.com/doi/10.1002/dac.1036 |journal=International Journal of Communication Systems |language=en |volume=23 |pages=1–22 |doi=10.1002/dac.1036|s2cid=46507769 }}</ref>
[[Distributed computing|Distributed web applications]] should consider [[Distributed cache|distributed caching]].
==Parts of the system==
===Forward and reverse===
A forward cache is a cache outside the [[web server]]'s network, e.g. in the client's [[web browser]], in an [[ISP]], or within a corporate network.<ref>{{cite web |url=http://www.isaserver.org/tutorials/Understanding-Web-Caching-Concepts-ISA-Firewall.html |title=Understanding Web Caching Concepts for the ISA Firewall |first=Thomas |last=Shinder |access-date=27 February 2011 |date=2 September 2008 |work=[[ISA Server]] |archive-url=https://web.archive.org/web/20110723104247/http://www.isaserver.org/tutorials/Understanding-Web-Caching-Concepts-ISA-Firewall.html |archive-date=23 July 2011 |publisher=TechGenix Ltd.}}</ref> A network-aware forward cache only caches heavily accessed items.<ref name=":0">{{cite journal |url=http://www.research.att.com/export/sites/att_labs/techdocs/TD_7LAUDD.pdf |citeseerx=10.1.1.159.1786 |title=Network-Aware Forward Caching |first1=Jeffrey |last1=Erman |first2=Alexandre |last2=Gerber |first3=Mohammad T. |last3=Hajiaghayi |first4=Dan |last4=Pei |first5=Oliver |last5=Spatscheck |journal=[[AT&T Labs]] |year=2008 |access-date=11 March 2019 |archive-url=https://web.archive.org/web/20110401145549/http://www.research.att.com/export/sites/att_labs/techdocs/TD_7LAUDD.pdf |archive-date=1 April 2011 |pages=291–300}}</ref> A [[proxy server]] sitting between the client and web server can evaluate [[HTTP]] headers and choose whether to store web content.
A reverse cache sits in front of one or more web servers, accelerating requests from the Internet and reducing peak server load. This is usually a [[content delivery network]] (CDN) that retains copies of web content at various points throughout a network.
===HTTP options===
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