Kobolds are a type of monster in Dungeons & Dragons. They are a race of small industrious, cave-dwelling, reptilian humanoids that come in various colors. Kobolds in 5th Edition differ from previous editions and from other depictions of Kobolds in other media. Kobolds originally being akin to a mischievous trickster household or mine spirit much like the Boggart, Goblin, Puck, or Gnome in European folklore.
Then being adapted as a vaguely magical monster found in caves and dungeons more or less interchangeable with goblins in the 1st Edition of Dungeons & Dragons.
Then in 2nd Edition they are given a distinct appearance of being short monkey like humanoids, with rat-like tails, and scaley/mangey hides.
In 3rd Edition greater emphasis is put on their reptilian features were given lore stating that they worship dragons.
4th Edition fully fleshed out the similar Dragonborn race and gave them greater emphasis on their relationship to dragons and other reptilian races like Dragonborn and Lizans.
In 5th Edition all the history of Kobolds has culminated into their current design. Kobolds are a species of small anthropomorphic reptiles standing no more than 3 feet tall with sinewy muscles, scaled hides, digitigrade legs with 3 toes, 4 long clawed like fingers, horns, a alligator's snout, and long rat-like tails. They are notorious for dwelling in caves, dungeons, mazes, ruins and other subterranean structures where they can create ingenious an deadly traps and use guerrilla tactics.