In Liquid, you can include a hyphen in your tag syntax {{-, -}}, {%-, and -%} to strip whitespace from the left or right side of a rendered tag.
Normally, even if it doesn’t output text, any line of Liquid in your template will still output a blank line in your rendered HTML:
Input
{% assign my_variable = "tomato" %}{{ my_variable }}
Notice the blank line before “tomato” in the rendered template:
Output
tomato
By including hyphens in your assign tag, you can strip the generated whitespace from the rendered template:
Input
{%- assign my_variable = "tomato" -%}{{ my_variable }}
Output
tomato
If you don’t want any of your tags to output whitespace, as a general rule you can add hyphens to both sides of all your tags ({%- and -%}).