Por supuesto.

A natural Spain Spanish pronunciation is roughly:

por swes-TO

A bit more closely:

• por → the r is a light tap
• supuesto → su-PUES-to, with the stress on pues

Notes:

• The u in puesto is pronounced, so it is not like pesto
• The s is clearly pronounced
• In normal speech, por supuesto often sounds smooth and connected rather than word-by-word

Because por supuesto is a fixed expression.

Here, supuesto comes from a past participle/adjective, but in this phrase the whole expression works like an adverbial expression meaning something like a strong, natural confirmation.

Using only supuesto by itself would not normally work as the same standalone reply. Native speakers use the full phrase por supuesto.

Literally, supuesto comes from the verb suponer and can mean something like supposed, assumed, or presumed, depending on context.

But in por supuesto, it is best to learn the whole thing as one expression. The literal pieces are less important than the fact that it functions as a set phrase.

So for learners, it is much more useful to remember:

• por supuesto = one complete expression
• not something you should usually analyze word by word in conversation

Yes, absolutely. That is one of its most common uses.

For example:

• ¿Me puedes ayudar?
• Por supuesto.

It works very naturally as a complete reply, especially when you want to sound willing, confident, or reassuring.

It is neutral and very common. It works in:

• casual conversation
• polite conversation
• more formal situations

It is not slang, and it is not especially stiff either. That makes it very useful.

In Spain, it sounds perfectly natural in everyday speech, though in very casual situations people may also use alternatives like claro.

Both can be used to agree strongly or say that something is obvious or completely fine, but they feel slightly different.

• claro is often more casual and conversational
• por supuesto can sound a bit stronger, more deliberate, or a little more polished

For example:

• ¿Vienes mañana?
  • Claro.
  • Por supuesto.

Both are correct.
Very generally:

• claro = very common, relaxed
• por supuesto = equally common, but slightly more emphatic or polished

Yes. A very common pattern is:

Por supuesto que...

For example:

• Por supuesto que voy.
• Por supuesto que sí.

The que introduces what follows and makes the statement feel complete and emphatic.

You can also simply say:

• Por supuesto.

So both are possible:

• standalone reply
• start of a longer sentence

Not always.

You can say:

• Por supuesto.
• Por supuesto que sí.

The version with que sí is more explicit and emphatic, especially when answering a yes/no question.

Compare:

• ¿Te gustó?
  • Por supuesto.
  • Por supuesto que sí.

Both are natural. The second one sounds a bit fuller and stronger.

Sometimes, yes. It is positive and natural, but it can sound stronger than a simple sí.

For example:

• If someone asks a very routine question, sí might be enough
• por supuesto can add warmth, enthusiasm, reassurance, or emphasis

That is usually a good thing, but if the situation is very neutral, it may sound slightly more emphatic than needed.

So:

• sí = basic yes
• por supuesto = stronger, warmer, more assured yes

Both are used in Spain and both can express strong agreement or certainty.

Very roughly:

• por supuesto = of course, certainly
• desde luego = certainly / definitely / of course

In modern everyday speech, many learners will hear por supuesto and claro more often in simple conversational replies. Desde luego is still common, but can sometimes sound a little more marked depending on tone and context.

For most learners, por supuesto is a very safe and versatile choice.

Because here it is written as a complete standalone sentence.

If it appears alone as a reply in writing, it usually takes normal sentence punctuation:

• Por supuesto.

If it is inside a longer sentence, the punctuation changes accordingly:

• Por supuesto, te ayudaré.
• ¿Por supuesto? would be unusual unless you were questioning the phrase itself or repeating it skeptically

So the period is not part of the expression itself; it just matches how the sentence is being used.