The item ID for Prismatic Shard in Stardew Valley is:
The above cheat code applies to all platforms including PC/Mac (Steam), XBOX One, PS4 and the Nintendo Switch.
Spawning items in Stardew Valley is not done via commands, but rather through a cheat in which you must set your character's name, or the name of an animal, to the item code of the item you wish to spawn surrounded by [ and ].
To spawn this item using an animal's name, visit Marnie's Ranch, speak to Marnie and purchase an animal (we recommend a chicken as it is cheapest). Name the animal  and press OK. You will then receive the prismatic shard item.
You can only set your character's name once, at the start of the game (when you create your world), for this reason we recommend you use the animal name method. If you do wish to use this method, first set your character's name to  when creating your save. Whenever you speak to a villager that says your name in dialogue (for example Gus at the Stardrop Saloon) you will be given the prismatic shard item.
If you need more help with spawning prismatic shard, we have a detailed guide on our blog - click here to visit that page.
Prismatic shards are rare items - infact, one of the rarest items in the game. There are many ways to obtain them, including iridium nodes and fishing treasure cheats. It is used to make the galaxy sword. Other uses include gifting to people within the game and as an offering to the Dark Shrine of Selfishness resulting in the removal of your children (if you have any).
A very rare and powerful substance with unknown origins.