La libro estas tro kara.

La is the definite article in Esperanto. It means the.

So la libro means the book, referring to a specific book.
A useful thing to remember is that la never changes form. It stays la no matter whether the noun is singular, plural, subject, or object.

Libro is the basic singular noun form, and Esperanto nouns normally end in -o.

So:

• libro = book
• libroj = books

In this sentence, the book is the subject, so the basic form libro is used.

Estas is the present-tense form of esti, meaning to be.

Esperanto verbs do not change according to person or number. That means the same form is used with I, you, he, they, the book, and so on.

Examples:

• Mi estas = I am
• Vi estas = you are
• La libro estas = the book is
• Ili estas = they are

That makes Esperanto verb conjugation much simpler than English.

Tro means too in the sense of excessively or more than is desirable.

So tro kara means too expensive or too dear, not just very expensive.

A very common comparison is:

• tre = very
• tro = too

So:

• tre kara = very expensive / very dear
• tro kara = too expensive / too dear

Because tro modifies the adjective kara, and in Esperanto words like tro usually come before the word they describe.

So:

• tro kara = too expensive / too dear

This is similar to English, where too comes before the adjective: too expensive.

Because kara is a predicate adjective after estas, and predicate adjectives do not take the accusative -n just because the sentence has a verb.

In this sentence:

• la libro is the subject
• estas links the subject to its description
• kara describes the subject

So kara stays in the nominative form.

Compare:

• La libro estas kara. = The book is expensive/dear.
• Mi aĉetas la libron. = I buy the book.

In the second example, libron gets -n because it is the direct object.

In Esperanto, adjectives end in -a.

So kara is an adjective meaning something like dear, costly, or expensive, depending on context.

Adjectives agree with the noun they describe in number and case. Here the noun is singular and not accusative, so the adjective is also singular and basic in form:

• libro → singular
• kara → singular adjective

If the noun were plural, the adjective would also be plural:

• La libroj estas tro karaj. = The books are too expensive.

That is a very natural question. Kara often means dear in the emotional sense, like beloved or dear to someone. But it can also mean dear in the older English sense of costly or expensive.

So context matters.

With libro, the sentence is usually understood as talking about price: The book is too expensive.

Still, many learners more often meet multekosta for expensive, because it is clearer and more specific.

So:

• kara can mean dear / costly
• multekosta very clearly means expensive

Because there is no direct object.

This sentence is built like:

• subject: La libro
• linking verb: estas
• description: tro kara

The accusative ending -n is mainly used for direct objects and in some other special cases, but not for the subject or for a predicate adjective after esti.

So no word here needs -n.

Yes, Esperanto word order is fairly flexible, but La libro estas tro kara is the most neutral and natural order.

This follows the common pattern:

• subject + verb + complement

You might see different word order for emphasis, but for a learner, this standard order is the best one to use first.

You can leave out la, but the meaning changes.

• La libro estas tro kara. = The book is too expensive.
• Libro estas tro kara. = A book is too expensive / Book is too expensive.

Without la, it sounds less specific and can feel more general or less natural depending on context. If you mean one particular book, la is the right choice.