The good news is they're fairly easy to tell apart with a little information.
|Language||"Ji" (寺) is the Japanese character (kanji) for temple (e.g. Ryoan-ji temple). It can also be pronounced "dera" and "tera" (e.g. Kiyomizu-dera temple)||"Jingu" (神宮) are the Japanese characters (kanji) for shrine (e.g. Meiji-jingu). This can also be pronounced "jinja".|
|Usual Architectural Features||Large bell||Entrance gate (torii)|
The Bad NewsFor hundreds of years, Buddhism and Shinto were somewhat mixed in Japan (especially before 1868). Therefore, some temples look like shrines and some shrines look like temples. There are also shines inside temples and vice versa. This makes it more difficult to tell temples and shrines apart.
Rule of ThumbTemple architecture tends to reflect Buddhist thinking. This means that temples are wabi-sabi, simple, austere, modest, intimate and natural. Japanese temples have a feel that's all there own — once you've been to a few you'll be able to identify them from these qualities alone.
Shinto is a indigenous Japanese religion that worships a variety of kami (gods). Many of Shinto's gods are gods of nature. At one time (before 1946) Japan's Emperor was also considered a god. Shinto was once intertwined with the Emperor and Japanese government. Shrines tend to have glorious, colorful, imperial designs.
Buddhist Monks vs Shinto PriestsAnother reliable (not infallible) way to tell temples from shrines is to look at the monks and priests.
Buddhist Monks dress in simple and austere robes.
Shinto priests dress flashy — there's no other way to put it.