Here's a cheap one
I position the brake hoods on the handlebars, so that they are in a horizontal extension from the top of the handlebars.
Then I take a piece of string.
And I place it horizontally at the base of the top of the brake hood, and by parallax with the handlebars, I can see if they are at the same height.
Otherwise, I raise or lower one of the two brake hoods.
Then I measure the distance from the tip of the brake hood to, for example, the opposite side where the stem attaches to the handlebars.
It should be identical on both sides.
Otherwise, I rotate one of the brake hoods inward or outward.