"It does exactly what it says on the tin" (often quoted as "does what it says on the tin") was originally an advertising slogan in the United Kingdom, which then became a common idiomatic phrase.

It originated in a series of television advertisements by the woodstain and wood-dye manufacturer Ronseal, initiated in 1994[3] and still being broadcast as of 2016.

Source: https://en.wikipedia.org/wiki/Does_exactly_what_it_says_on_t...