Your Dexterity score increases by 2, and your Constitution score increases by 1.

Ratfolk live quickly, having a lifespan shorter than most races - even humans.  They are considered adults by 14 and rarely live past their 50s.

Ratfolk have a rather frantic, hurried nature and very few structured societies in the world, thus they tend towards the chaotic.  Neutral or even lawful Ratfolk are not unheard of, however.  They do not show any particular bent towards good or evil and can be found anywhere on the alignment spectrum.

Ratfolk average just under 3 feet in height and weigh about 35 pounds.  Your size is Small.

Your base walking speed is 25 feet.

Accustomed to life underground, you have superior vision in dark and dim conditions. You can see in dim light within 60 feet of you as if it were bright light, and in darkness as if it were dim light. You can’t discern color in darkness, only shades of gray.

Whenever you make an Intelligence (Investigation) or Wisdom (Perception) check involving your sense of smell, you have advantage and are considered proficient in the relevant skill.

You have advantage on all saving throws triggered by consuming something.

You have a climbing speed of 20 feet.

You can move through the space of any creature that is of a size larger than yours.

You are proficient with your unarmed strikes, which deal 1d4 slashing damage on a hit.

You can speak, read, and write Common and Ratskree.  Ratskree is a remarkably difficult language for other races to learn, as not only is it spoken very quickly (a trait often carried over into the race's usage of Common) but also often incorporates head and tail movements for emphasis as well as different pitches of squeaks to convey mood and tone.  Uncommon as it is, the written version of the language likewise includes onomatopoeia of such sounds and even formal documents often have illustrations or other scribblings among the text.