Learn Hardcore German: Ohne gutes Werkzeug wird die Reparatur des Fahrrads schwer. - Without good tools the repair of the bicycle is difficult.

Because after ohne you often drop the article when speaking in general terms. In that case the adjective (gutes) takes a strong ending to show case, gender, and number.

What case does ohne govern, and how do we know gutes Werkzeug is in that case?

The preposition ohne always takes the accusative case. We see gutes Werkzeug is accusative neuter singular by the adjective ending -es (strong declension) and the lack of an article.

How is the strong adjective ending determined in gutes Werkzeug?

With no article present, the adjective must carry all the information. For a neuter noun in the accusative singular, the strong declension ending is -es, so gut becomes gutes.

Why is des Fahrrads in the genitive case, and why does Fahrrad take -s?

des Fahrrads shows possession (“the repair of the bicycle”). Reparatur is a noun that takes a genitive object. Fahrrad is neuter, and most neuter nouns form the genitive singular by adding -s (or -es), so it becomes des Fahrrads.

What role does wird play here?

Here wird functions as a linking verb meaning “becomes.” It’s not the passive voice; rather it connects the subject (die Reparatur des Fahrrads) to the predicate adjective (schwer).

Why is schwer placed at the end of the sentence?

In a German main clause, the finite verb occupies the second position (wird). Other elements, like predicate adjectives, typically come after the verb and object, often ending up at the very end.

Could you use schwierig instead of schwer, and what’s the nuance?

Yes, schwierig also means “difficult.” The nuance is that schwierig only conveys difficulty, whereas schwer can mean “heavy” or “difficult.” In this context both work, but schwierig is purely about difficulty.