Antes de pagar la cuenta, quiero comprobar si el precio incluye la propina.

In Spanish, antes normally needs de before an infinitive.

• antes de pagar = before paying
• después de comer = after eating

So antes de + infinitive is the standard pattern when the subject is the same as in the main clause.

If the subject changes, Spanish often uses a full clause instead:

• Antes de pagar la cuenta, quiero comprobar... = I am the one paying and checking.
• Antes de que paguemos la cuenta... = before we pay the bill

In restaurant Spanish, la cuenta is the normal word for the bill/check.

Literally, cuenta can mean account, calculation, or bill, depending on context. In a restaurant, it means the amount owed.

Common phrases:

• La cuenta, por favor. = The bill, please.
• Pagar la cuenta. = To pay the bill.

For a learner of Spanish from Spain, la cuenta is exactly the natural term to expect in this context.

Here, comprobar means to check, to verify, or to make sure.

So:

• quiero comprobar = I want to check / I want to make sure

In Spain, comprobar is very common in this sense. Similar verbs are:

• verificar = to verify
• revisar = to review/check
• mirar = to look at/check informally

In this sentence, comprobar sounds natural because the speaker wants to confirm whether the tip is included.

These are two different words:

• si = if / whether
• sí = yes

In this sentence, si introduces an indirect yes/no question:

• quiero comprobar si el precio incluye la propina
  = I want to check whether the price includes the tip

So there is no accent because it means whether, not yes.

Because si here means whether/if, introducing an indirect question, and Spanish normally uses the indicative after this kind of si.

• Quiero comprobar si el precio incluye la propina.
• No sé si viene mañana.

This is different from other uses of si in hypothetical sentences, such as:

• Si tuviera dinero, pagaría yo. = If I had money, I would pay.

So in your sentence, incluye is correct because the speaker is checking a fact.

El precio means the price, and it works well here. The speaker is referring to the amount being charged.

That said, Spanish could also use other words depending on nuance:

• el precio = the price
• el total = the total amount
• el coste = the cost

In a restaurant, many speakers might also say:

• quiero comprobar si la propina está incluida en el precio
• quiero comprobar si está incluida en el total

So el precio is correct and natural, though there are other possible ways to express the same idea.

Spanish uses definite articles much more often than English does.

So where English might say:

• includes tip

Spanish often says:

• incluye la propina

This does not necessarily mean a specific tip already known to everyone. It is just normal Spanish style to use the article with many nouns in general statements.

Other examples:

• Me duele la cabeza. = My head hurts.
• Toco la guitarra. = I play guitar.
• El café está frío. = The coffee is cold.

Because Spanish usually drops subject pronouns when they are not needed.

• quiero already tells you the subject is I
• so yo quiero is possible, but often unnecessary

Spanish prefers:

• Quiero comprobar...

You might include yo for emphasis or contrast:

• Yo quiero comprobarlo, pero él no. = I want to check it, but he doesn’t.

So leaving out yo is the most normal choice here.

The comma separates the introductory phrase from the main clause:

• Antes de pagar la cuenta, = introductory time expression
• quiero comprobar... = main clause

This is very similar to English:

• Before paying the bill, I want to check...

The comma helps readability and is standard punctuation here.

Yes. That is perfectly natural if the context already makes it clear that you mean the bill.

Compare:

• Antes de pagar la cuenta, quiero comprobar...
  More explicit
• Antes de pagar, quiero comprobar...
  Shorter, but still clear in a restaurant context

Spanish often omits things that are obvious from the situation.

Yes. La propina is the standard word for tip in Spain.

Useful expressions:

• dejar propina = to leave a tip
• la propina está incluida = the tip is included
• ¿Está incluida la propina? = Is the tip included?

A cultural note: in Spain, tipping exists, but it is generally less obligatory and less standardized than in places like the US. So this sentence is grammatically normal, but the real-life situation may vary depending on the restaurant.

Yes. Your sentence is correct, but Spanish offers several natural alternatives.

For example:

• Antes de pagar la cuenta, quiero comprobar si la propina está incluida.
• Antes de pagar la cuenta, quiero ver si el precio incluye la propina.
• Quiero comprobar, antes de pagar la cuenta, si el precio incluye la propina.

Among these, si la propina está incluida is especially common because it focuses directly on the tip rather than on the price.

So the original sentence is good, but it is not the only natural option.