all that glitters is not gold

• all that glisters is not gold (older form)
• all that glitters (shortened form)

Calque of Latin nōn omne quod nitet aurum est (“not all that shines is gold”). Popularized by William Shakespeare in The Merchant of Venice, see quotations.

all that glitters is not gold

1. Things that appear valuable or worthwhile might not actually be so; things that look nice might not be as good as they look.
   • c. 1596–1598 (date written), William Shakespeare, “The Merchant of Venice”, in Mr. William Shakespeares Comedies, Histories, & Tragedies […] (First Folio), London: […] Isaac Iaggard, and Ed[ward] Blount, published 1623, →OCLC, [Act II, scene vii], page 171, column 1:

     All that gliſters is not gold,
     Often haue you heard that told;

• you can't judge a book by its cover
• looks can be deceiving

• fool's gold
• bright shiny object

• Gregory Y. Titelman, Random House Dictionary of Popular Proverbs and Sayings, 1996, →ISBN, p. 9.

• All that glitters is not gold on Wikipedia.Wikipedia