der Hammer
hammer
A tool with a heavy metal head on a handle, used for striking something, for example nails.
Ich brauche einen Hammer, um das Bild an die Wand zu hängen.
I need a hammer to hang the picture on the wall.

hammer
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hammer
A tool with a heavy metal head on a handle, used for striking something, for example nails.
Ich brauche einen Hammer, um das Bild an die Wand zu hängen.
I need a hammer to hang the picture on the wall.

In colloquial speech, 'der Hammer' (amazing/outrageous) is a very common expression for something amazing or surprising. It can be meant both positively (great) and negatively (outrageous).
Du hast die Tickets umsonst bekommen? Das ist ja der Hammer!
You got the tickets for free? That's amazing!
This colloquial meaning is often used in the fixed expression 'Das ist der Hammer!' (That's amazing!/That's outrageous!) or as the short exclamation 'Der Hammer!' to express strong emotions.
Das Konzert gestern war der absolute Hammer!
The concert yesterday was absolutely amazing!
Whether the tool or the colloquial expression is meant can easily be recognized from context. If it is about building or repairing, it is the tool. In emotional reactions, it is the exclamation.
Für dieses Regal brauche ich Schrauben und einen Hammer.
For this shelf, I need screws and a hammer.
When it comes to the tool, typical verbs are 'einen Nagel einschlagen' (to drive in a nail), 'mit dem Hammer schlagen' (to hit with a hammer), or simply 'den Hammer benutzen' (to use the hammer).
Er schlug mit dem Hammer einen Nagel in die Wand.
He drove a nail into the wall with the hammer.
madness / amazing
'der Hammer' and 'der Wahnsinn' can both express a strong reaction in colloquial language. You use them when something is unbelievable, impressive, or very surprising. 'der Hammer' often sounds like a direct judgment: something is extremely good, bad, or outrageous. 'der Wahnsinn' can also be used as an exclamation for something very impressive, but it also fits something very unreasonable or dangerous. Learners may confuse the words because both sound strong and emotional in everyday language. Pay attention to the context: 'Hammer' often directly evaluates a thing, while 'Wahnsinn' can also emphasize the craziness of an action.

Der Blick vom Turm über die Stadt war wirklich der Hammer.
The view from the tower over the city was truly amazing.
Bei diesem Sturm mit dem Fahrrad zu fahren ist doch Wahnsinn.
Riding a bike in this storm is madness.