Jamstvo za izvedene radove mora vrijediti.

Here jamstvo means guarantee or warranty.

In this sentence, it is the subject of the sentence:

• Jamstvo = the guarantee / warranty

In legal, technical, or business contexts, jamstvo is very common for a formal guarantee on work, products, or services.

Because it is the subject of the sentence.

The basic structure is:

• Jamstvo = subject
• mora vrijediti = must be valid / must apply

So jamstvo stays in the nominative singular.

Also, jamstvo is a neuter noun, and its dictionary form is already jamstvo.

It means for the completed works or for the work that has been carried out.

Breakdown:

• za = for
• izvedene = carried out, performed, completed
• radove = works / jobs / construction work items

So the whole phrase describes what the guarantee applies to:

• jamstvo za izvedene radove = guarantee for completed works

In English, this often sounds more natural as:

• warranty for completed work
• guarantee for work performed

Because the preposition za here takes the accusative case.

So:

• nominative plural: radovi
• accusative plural: radove

Since the phrase is za + accusative, we get:

• za radove
• za izvedene radove

This is a very common pattern in Croatian:

• za kuću = for the house
• za djecu = for the children
• za radove = for the works

Yes. In this sentence, izvedene functions like an adjective.

It comes from the verb izvesti / izvoditi, which can mean to carry out, to perform, or to execute.

Here izvedene is a participial adjective meaning:

• carried out
• performed
• completed

It agrees with radove:

• masculine plural accusative animate/inanimate? Here effectively plural form matching radove
• so we get izvedene radove

You can think of it as similar to English completed works or work performed.

Because the subject is jamstvo, which is singular.

• jamstvo = singular
• therefore: mora = must

Even though radove is plural, that is not the subject. It is part of the prepositional phrase za izvedene radove.

So:

• Jamstvo mora vrijediti. = The guarantee must be valid.
• If the subject were plural, then you would use moraju.

For example:

• Jamstva moraju vrijediti. = The guarantees must be valid.

Good question. Vrijediti can indeed mean to be worth, but it also has another common meaning: to be valid, to apply, or to remain in force.

In this sentence, it means:

• to be valid
• to apply
• to remain effective

So:

• Jamstvo mora vrijediti. = The guarantee must be valid.

Compare:

• Ova knjiga vrijedi 10 eura. = This book is worth 10 euros.
• Karta vrijedi do petka. = The ticket is valid until Friday.

So the verb has more than one meaning, and context tells you which one is intended.

Yes, in many contexts važiti could also work.

• vrijediti = to be valid / to be worth / to apply
• važiti = to be valid / to apply

So a sentence like:

• Jamstvo mora važiti.

would also make sense.

That said, vrijediti is very natural in contexts involving warranties, guarantees, tickets, legal validity, time limits, and similar things. Native usage may vary slightly by region or register, but the original sentence sounds normal.

Here radovi usually means works, especially in a practical or technical sense:

• construction works
• repair works
• installation works
• completed jobs on a project

It does not usually mean work in the abstract sense of employment or labor in general.

So in this sentence, izvedeni radovi suggests work that has been physically carried out, often by a contractor or company.

Because Croatian has no articles like English the and a/an.

So:

• jamstvo can mean a guarantee or the guarantee
• radove can mean works or the works

The exact meaning depends on context.

In many real situations, the sentence would be understood as:

• The warranty for the completed works must be valid

even though Croatian does not mark the explicitly.

Croatian word order is fairly flexible, although some orders sound more natural than others.

The original:

• Jamstvo za izvedene radove mora vrijediti.

is neutral and natural.

You could also rearrange it for emphasis, for example:

• Jamstvo mora vrijediti za izvedene radove.

This puts the focus slightly differently, but the meaning stays close.

Still, the original version is probably the best choice in formal or written language because it keeps jamstvo za izvedene radove together as one clear noun phrase.

Yes, it sounds fairly formal and administrative/technical.

Words like:

• jamstvo
• izvedeni radovi
• vrijediti

are very common in:

• contracts
• construction documents
• legal texts
• warranty terms
• business communication

A more everyday conversational Croatian sentence might be phrased differently depending on context, but this sentence is perfectly normal in formal written Croatian.