An art and a science. Code and applications versus design aesthetics. Understanding value of easy and cheap v. audience retention and conversions. Responsive website designs matter. Other tools are other language architecture for databases, user authentication and email services. Software is required as text editors, command line interface, and version control -- while web designers ensure code is aesthetically pleasing and user-friendly and most likely implement graphic design products like Adobe Photoshop, Illustrator, or Inkscape.
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Mobile-friendly websites can also be developed as content management systems (CMS). This not only keeps costs minimized but also facilitates a content marketing strategy, can that also formulate basis for an authority marketing campaign to leverage online presence for lead generation and sales conversion.