Verb[dictionary] + ばかり – nothing but / on the verge of
Noun + ばかり – nothing but / approximately
Number/Quantity + ばかり – approximately
The particle ばかり has several distinct uses depending on the form it attaches to. It can express that something just happened, that someone does nothing but a certain action, or give an approximate amount.
When attached to the past tense of a verb, ばかり indicates that an action has just been completed. The focus is on the recency of the event.
This usage emphasizes that not much time has passed since the action occurred. The speaker may use it to explain why a certain state exists or why something isn't ready yet.
When attached to a noun or the て-form of a verb (with いる), ばかり expresses that someone does nothing but that action, or that there is only that thing. It often carries a negative or critical nuance, implying excess or imbalance.
With nouns, ばかり replaces or follows the particle を, but generally replaces particles like が and を directly. Other particles like に, で, and と can appear before or after ばかり.
With quantities, ばかり means "about" or "approximately". This usage is somewhat literary and less common in casual speech, where くらい or ぐらい are preferred.
In casual spoken Japanese, ばかり is frequently shortened to ばっかり or even ばっか.