Don't write a lowercase s or es in parentheses, "(s)" or "(es)", after a noun to indicate both singular and plural. Choose the best option for your documentation. In most cases, using the plural works best for understanding the sentence.

If it's important to include both singular and plural, try including the phrase "one or more".

Do this	Don't do this
The endpoint returns the current webhook key. The endpoint returns the current webhook keys. The endpoint returns one or more of the current webhook keys. The endpoint returns all of the current webhook keys.	The endpoint returns the current webhook key(s).

For acceptable uses of parentheses in your writing, see Parentheses.