Natural 20 - Auto success?

[Relic]

Basically, what the title advertises. Is a natural 20 an auto-success for skill checks, ability checks, and attack rolls? I thought I read it somewhere in the core books but after looking front to back I cannot find where I read it. Thanks in advance.

 

[Kordeth]

Basically, what the title advertises. Is a natural 20 an auto-success for skill checks, ability checks, and attack rolls? I thought I read it somewhere in the core books but after looking front to back I cannot find where I read it. Thanks in advance.

Only attack rolls. PHB p. 276.

 

[kouk]

You are probably thinking of the "Critical Success and Failure" Houserule on page 189 of the DMG.