everyday / every day
One is an adjective. One is how often. The space is doing real work.
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Wrong: I check it everyday.
Right: I check it every day.
How often. Two words.
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Wrong: These are my every day shoes.
Right: These are my everyday shoes.
Describing the shoes. One word.
The test
Try “each day.” If it fits, you want the two-word version: every day.
I check it each day works, so every day. These are my each day shoes doesn’t, so everyday.
What the one-word version means
Everyday is an adjective meaning ordinary or routine—everyday problems, everyday clothes. It describes a noun and it never tells you how often something happens.
Same pattern as anytime vs any time and awhile vs a while: closing the space turns a phrase into a describing word.
Now go check whether you meant each day.