Ein Handwerker aus der Nachbarschaft bringt Werkzeug mit, aber er ist nicht der Klempner.

A tradesperson from the neighborhood brings tools along, but he isn’t the plumber.

Breakdown of Ein Handwerker aus der Nachbarschaft bringt Werkzeug mit, aber er ist nicht der Klempner.

• sein: to be
• nicht: not
• er: he
• aber: but
• aus: from
• mitbringen: to bring along
• der: the; (feminine, dative)
• die Nachbarschaft: the neighborhood
• der Klempner: the plumber
• der Handwerker: the tradesperson
• das Werkzeug: the tools

Questions & Answers about Ein Handwerker aus der Nachbarschaft bringt Werkzeug mit, aber er ist nicht der Klempner.

Why does the sentence start with Ein Handwerker and not Der Handwerker?

Ein Handwerker means a (certain) tradesman/handyman—someone not previously identified to the listener/reader.
Der Handwerker would sound like the tradesman (a specific one already known from context).

What case is Ein Handwerker in, and how do I know?

It’s nominative, because Ein Handwerker is the subject doing the action (bringt).
The verb ending -t in bringt also matches er / ein Handwerker (3rd person singular).

Why is it aus der Nachbarschaft and not aus die Nachbarschaft?

Because aus always takes the dative case.
Nachbarschaft is feminine (die Nachbarschaft), so dative feminine is der Nachbarschaft.

Does Nachbarschaft mean the same as English neighborhood?

Usually yes: die Nachbarschaft can mean the neighborhood/area nearby, and it can also mean the neighbors as a community (the general “neighborhood” feeling/group). In this sentence it’s basically from the neighborhood.

Why is mit at the end in bringt Werkzeug mit?

Because mitbringen is a separable verb (mit- + bringen).
In a main clause, the conjugated part (bringt) goes in position 2, and the separable prefix (mit) goes to the end:

• Er bringt Werkzeug mit.
  In a subordinate clause, it stays together:
• …, weil er Werkzeug mitbringt.

Why is there no article before Werkzeug?

Werkzeug is often used like a mass/collective noun (similar to English tools/equipment), so German commonly says Werkzeug without an article when speaking generally.
If you want to be more specific, you can add one, for example:

• sein Werkzeug = his tools
• das Werkzeug = the (specific) set of tools
  Or you can use plural Werkzeuge if you mean individual tools.

Is the comma before aber required?

It’s often used, but with aber the comma is generally optional when connecting two main clauses. Many writers include it because it makes the pause/contrast clearer:

• …, aber … feels very natural and readable.

Why does German repeat the subject with aber er ist …? Could you drop er?

In normal German you don’t drop the subject in a new clause. Each finite clause typically needs its own explicit subject:

• …, aber er ist … (standard)
  Leaving it out would sound incomplete or unnatural here.

Why is it nicht der Klempner and not kein Klempner?

nicht der Klempner usually implies not the (specific) plumber you’re thinking of/expecting (e.g., “He’s not the plumber”).
kein Klempner means not a plumber at all (profession/identity).
So the definite article der adds the idea of a particular plumber.

Why is the negation nicht used here instead of kein?

German typically uses kein to negate an indefinite noun phrase (like ein Klempner):

• Er ist kein Klempner. = He isn’t a plumber.
  But with a definite noun phrase (der Klempner), you negate it with nicht:
• Er ist nicht der Klempner. = He isn’t the (specific) plumber.

Can you say Er ist nicht Klempner without an article?

Not normally in standard German. For professions, you usually say:

• Er ist Klempner. (no article in the positive)
  But the natural negative is:
• Er ist kein Klempner.
  If you use nicht, it’s typically with something definite/specific: nicht der Klempner.