previewer

/ˈpriːvjuːər/
noun
  1. A person who looks at something before it is officially released or shown to the public, especially to evaluate or check it.
    • As a book previewer, she reads manuscripts and suggests changes to the author.
    • The film previewer gave the movie a positive review before its release.
    • The software company hired a previewer to test the new app for bugs.
  2. A tool or feature that allows someone to see a sample or early version of something, such as a document, image, or video.
    • The photo editor has a built-in previewer so you can see changes before saving.
    • Use the PDF previewer to check the layout before printing.
    • The website's previewer shows how your post will look on mobile devices.
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