Energetická třída je dobrá.

Because energetická třída is a feminine singular noun phrase, and Czech adjectives must agree with the noun in gender, number, and case.

• dobrý = masculine singular
• dobrá = feminine singular
• dobré = neuter singular or plural in some contexts

Since třída is feminine, the adjective must be feminine too:

• dobrá třída
• Energetická třída je dobrá.

The same agreement also happens in energetická, which matches třída.

The ending -á shows that energetická is a feminine singular adjective agreeing with třída.

The base adjective is something like energetický / energetická / energetické, and its form changes depending on the noun:

• energetický = masculine
• energetická = feminine
• energetické = neuter

Because třída is feminine, you say:

• energetická třída

This is exactly the same kind of agreement as in:

• dobrá kniha = a good book
• nová škola = a new school

A very common clue is the ending. Many Czech nouns ending in -a are feminine, and třída is one of them.

So:

• třída = feminine noun

That means adjectives with it must also be feminine:

• energetická třída
• dobrá třída

Be careful, though: while -a often signals feminine gender, it is not a 100% universal rule. But for třída, feminine is correct.

Je is the 3rd person singular form of the verb být = to be.

So here:

• je = is

The sentence structure is:

• Energetická třída = subject
• je = is
• dobrá = good

So grammatically it works like:

• The energy class is good.

Other forms of být in the present tense are:

• jsem = I am
• jsi / jste = you are
• je = he/she/it is
• jsme = we are
• jsou = they are

Usually, in a normal present-tense sentence like this, no. You normally keep je.

So:

• Energetická třída je dobrá. = correct

Leaving it out:

• Energetická třída dobrá.

would sound incomplete in standard Czech.

Czech often drops subject pronouns like já, ty, oni, but it does not usually drop the verb to be in this kind of sentence.

Yes, other word orders are possible in Czech, but they change the focus or emphasis.

The neutral, normal order is:

• Energetická třída je dobrá.

This is the most natural way to simply state the fact.

You could also say:

• Dobrá je energetická třída.

But that sounds more marked, as if you are emphasizing good or contrasting it with something else.

Czech word order is more flexible than English because grammatical relationships are often shown by endings, not just position. Still, the basic neutral order is usually the best one for learners to use first.

It is an adjective.

It describes the noun phrase energetická třída, and it agrees with it in gender and number.

That is why it appears as dobrá and not in some invariable form.

Compare:

• dobrá třída = a good class/rating
• Třída je dobrá. = The class/rating is good.

An adverb would describe a verb, adjective, or another adverb, not a noun. Here dobrá is describing what the subject is like, so it is adjectival.

Because after být (to be), Czech commonly uses an adjective as a predicate adjective, just like English does in is good.

So:

• je dobrá = is good

The adjective still agrees with the subject:

• škola je dobrá = the school is good
• auto je dobré = the car is good
• film je dobrý = the film is good

This is very normal in Czech.

Třída can be tricky for English speakers because of tř and the long í.

A rough guide:

• tř = a special Czech sound with ř, which has no exact English equivalent
• í = a long ee sound
• da = like da, but with Czech pronunciation

So roughly: tree-da, but that is only approximate, because ř is not the same as English r or zh.

The sound ř is one of the most famous difficult Czech sounds. In třída, it comes after t, which makes it even harder for learners.

ř is a uniquely Czech sound. There is no perfect English equivalent.

A useful beginner way to think about it is:

• it is somewhat like an r mixed with a zh sound (like the s in measure), but that is only an approximation

In třída, the sound is devoiced because of the preceding t, so it may sound a bit closer to a voiceless version of that sound.

For beginners, it is fine to aim for something approximate at first. Native speakers know ř is hard for foreigners. The important thing is to keep practicing and listening.

The accent mark in Czech usually shows vowel length, not stress.

So:

• á = long a
• í = long ee

In this sentence:

• energetická has long á
• třída has long í
• dobrá has long á

This means those vowels are held a little longer than short vowels.

Important: Czech stress is usually on the first syllable of the word, regardless of these accent marks. So the marks do not tell you where to stress the word; they tell you that the vowel is long.

Yes. It is the subject of the sentence, so it is in the nominative case.

The sentence answers the question:

• Co je dobrá? = What is good?

And the thing that is good is energetická třída.

You can also see nominative agreement in the adjective forms:

• energetická
• dobrá

Both are feminine singular nominative, agreeing with třída.

Yes, that would be possible if you want to say That is a good energy class/rating.

Compare:

• Energetická třída je dobrá. = The energy class is good.
• To je dobrá energetická třída. = That is a good energy class.

The first sentence talks about a specific subject and says what quality it has. The second points to something with to = that/it and identifies it.

So the structure changes depending on what exactly you want to say.

In many contexts, dobrý / dobrá / dobré can cover meanings like good, fine, or sometimes nice, depending on context.

In this sentence, with energetická třída, the most natural meaning is good rather than nice. It suggests a favorable or high-quality energy rating/classification.

So while dobrá is a broad adjective, the context makes good the best interpretation here.

Yes. That means The energy class is very good.

You can add adverbs before the adjective:

• je dobrá = is good
• je velmi dobrá = is very good
• je celkem dobrá = is fairly good
• je opravdu dobrá = is really good

The adjective still stays feminine singular because it still agrees with třída.

Then the adjective forms would change to match the gender.

For example:

• masculine: Výsledek je dobrý. = The result is good.
• feminine: Třída je dobrá. = The class/rating is good.
• neuter: Auto je dobré. = The car is good.

So the pattern is:

• dobrý = masculine
• dobrá = feminine
• dobré = neuter

The same kind of change happens with many adjectives in Czech.