hacken
to chop
To cut something apart with strong, short blows, usually with a hatchet, an axe, or a large knife.
Für das Kaminfeuer müssen wir noch Holz hacken.
For the fireplace, we still need to chop wood.

to chop / hack
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to chop
To cut something apart with strong, short blows, usually with a hatchet, an axe, or a large knife.
Für das Kaminfeuer müssen wir noch Holz hacken.
For the fireplace, we still need to chop wood.

The core idea of 'hacken' (to chop/hack) is a short, forceful, and often repeated movement. This idea appears in many meanings: when chopping wood, doing garden work, when a bird pecks, or even when typing on a keyboard.
Der Gärtner hackt das Unkraut im Beet.
The gardener hoes the weeds in the bed.
The context usually makes the meaning of 'hacken' (to chop/hack) very clear. If it's about 'Holz' (wood), it means cutting apart. If it's about 'Computer' (computers) or 'Systeme' (systems), it means digital intrusion. If it's about the 'Garten' (garden), it means working the soil.
Er hat den ganzen Nachmittag Holz für den Winter gehackt.
He chopped wood for the winter all afternoon.
In the kitchen, 'hacken' (to chop) means to cut something very small with a knife. Typical examples are 'Zwiebeln hacken' (to chop onions), 'Knoblauch hacken' (to chop garlic), or 'Kräuter hacken' (to chop herbs).
Für die Soße müssen Sie eine Zwiebel und zwei Knoblauchzehen fein hacken.
For the sauce, you need to finely chop one onion and two cloves of garlic.
The meaning in the computer context is very common today and internationally understandable. You can say 'ein System hacken' (to hack a system), 'einen Account hacken' (to hack an account), or 'sich in ein Netzwerk hacken' (to hack into a network).
Er versucht, sich in das WLAN der Nachbarn zu hacken.
He is trying to hack into the neighbors' Wi-Fi.
The expression 'auf jemandem herumhacken' means to constantly criticize someone. The preposition is always 'auf' with the dative, and the 'herum-' emphasizes the repeated and annoying nature of the criticism.
Die Chefin hat den ganzen Tag auf ihm herumgehackt.
The boss picked on him all day.
The phrase 'in die Tasten hacken' is a colloquial and figurative description for very fast or loud typing on a keyboard. It is often used when someone is working under time pressure.
Ich muss den Artikel noch fertig schreiben und die ganze Nacht in die Tasten hacken.
I still have to finish writing the article and pound the keys all night.
When a mechanical part does not work smoothly, you say it 'hackt' (catches/sticks). The word describes a brief jamming or jerking, for example with a gearbox, a lock, or a drawer.
Der Schlüssel lässt sich nur schwer drehen, das Schloss hackt ein wenig.
The key is hard to turn; the lock sticks a little.
to criticize
'kritisieren' and 'hacken' are similar only in one specific expression: 'auf jemandem herumhacken' (to pick on someone). 'kritisieren' means to point out mistakes or negative points. This can be factual and happen just once. 'auf jemandem herumhacken' is colloquial and sounds unfair or petty. It means criticizing or treating someone badly again and again. Important: the simple verb 'hacken' has many other meanings and is not automatically a synonym for 'kritisieren'. For normal, factual criticism, 'kritisieren' fits. When the criticism is repeated and unpleasant, 'auf jemandem herumhacken' fits.

Emma ärgert sich, weil die Gruppe ständig auf ihr herumhackt.
Emma is annoyed because the group keeps picking on her.
Meine Nachbarin kritisiert den Lärm im Haus, aber sie bleibt freundlich.
My neighbor criticizes the noise in the building, but she stays friendly.