I agree/agreed rather than just agree. Grammatically , yes the article is required. You do hear people (often teenagers) say it without the article but it is far from accepted.
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RazerIs it necessary "grammatically" to use article "a" before the word bitYes.
Razeror would it do without it ?No. There are quite a few combinations that mean "to a very small degree" that require "a" grammatically: