Learn Hardcore Chinese: nǐ huílái le ma?

了 marks that a change has occurred or an action is completed. With 回来 (huílai, come back), 回来了 means “(has) come back” or “is back (now).” Adding 吗 turns the statement into a yes–no question: “Are you back (now)?” or “Have you come back?”
It’s fine to have both: 了 signals the aspect/state change; 吗 signals the yes–no question.

How is 你回来了吗 different from 你回来了 (without 吗)?

你回来了。 Neutral statement: “You’re back (now).”
你回来了吗？ Neutral info-seeking question: “Are you back (now)?”
你回来了？ (no 吗, rising tone) often sounds like a surprised confirmation: “Oh, you’re back?”

How do I answer this question naturally?

Yes: 回来了。 / 我回来了。
No (not yet): 还没(有)。 / 我还没(有)回来。
You can also add time: 刚回。 “(I) just got back.”

How do I negate the verb here? Do I use 不 or 没(有)?

Use 没(有) to negate completed actions or the change-of-state 了:

我没(有)回来。 “I didn’t come back / I haven’t come back.”
Use 不 for habitual/future refusal:
我不回来。 “I’m not (going to) come back.” (policy/decision)

Why is it 回来 and not 回去?

来 means movement toward the speaker; 去 means movement away from the speaker.

If the speaker’s “here” is the destination: 回来 (come back here).
If the destination is elsewhere (not where the speaker is): 回去 (go back there).
Examples:
Talking on the phone from home to someone outside: 你回来了吗？ “Are you back (home) now?”
At the office about someone going back home: 他回去了吗？ “Did he go back (home)?”

Can I just say 你回来吗 without 了?

Yes, but it shifts the meaning. 你回来吗？ typically asks about future or intention: “Will you come back?” / “Are you coming back?”
你回来了吗？ asks about a completed action/current state: “Are you back now?”

Where do 吗 and 了 go in the sentence?

The yes–no particle 吗 sits at the very end of the sentence.
了 comes after the verb phrase (回来) and before 吗: 你回来了吗？
If there’s a place word with 到, 了 comes after the verb phrase and place: 你回到家了吗？

Is 你回来了吗 the same as 你已经回来了吗?

你回来了吗？ “Are you back now?”
你已经回来了吗？ adds “already,” often expressing mild surprise: “Are you back already?” Both are grammatical; the second is more emphatic.

What’s the difference between 回 and 回来?

回 = “to return,” often used with a destination: 回家 (return home).
回来 = “to come back (toward here).”
回去 = “to go back (away from here).”
Examples: 你回家了吗？ (Did you go/come back home?) vs 你回来了吗？ (Are you back here?)

Can I say 回到 here? For example, 你回到了吗?

Not like that. 回到 needs a destination:

Correct: 你回到家了吗？ “Have you arrived back home?”
Also common: 你到家了吗？ “Have you arrived home?”

How else can I ask this as a yes–no question without 吗?

A-not-A: 你回不回来？ (future/intention)
With 没有: 你回来没有？ / 你回来了没有？ (colloquial: “Have you come back or not?”)
Rising intonation: 你回来了？ (often sounds like confirming/surprised)

I see both 你回来了吗 and 你回来了么 online. Are 吗 and 么 the same?

In standard writing, use 吗 for yes–no questions. 么 is often used informally online in place of 吗, but it’s nonstandard. Stick with 吗 in formal or careful writing.

Is 嘛 the same as 吗?

No. 吗 (ma) makes yes–no questions. 嘛 (ma) is an explanatory/softening particle, not a question marker.

Correct question: 你回来了吗？
你回来了嘛？ sounds like “you know, you’re back,” not a proper yes–no question.

How do tones work here? Any sandhi to watch?

Pronunciation: nǐ huílai le ma

你 (nǐ) is 3rd tone; before a non–3rd tone it’s often pronounced as a low (half) 3rd.
回 (huí) 2nd, 来 (lái) 2nd.
了 (le) neutral tone.
吗 (ma) neutral tone.

How would I ask “When did you come back?”

你是什么时候回来的？ (very natural)
你什么时候回来(的)？ (also used; 的 often appears in past-event questions like this)

How do I say “Have you ever come back (here) before?” using 过?

Use 过 for past experience: 你回来过吗？
This asks whether, at any time in the past, the person has (ever) come back here.

What’s the nuance of 你回来了吧?

吧 expresses a guess/assumption or seeks confirmation: 你回来了吧？ ≈ “You’re back now, right?” It’s softer and suggests the speaker expects “yes.”

Can I drop the subject 你?

Yes, if context makes it clear who you’re asking: 回来了吗？ “(Are you) back now?” Chinese often omits obvious subjects in conversation.

How would I address someone politely?

Use 您: 您回来了吗？ This is respectful toward elders, customers, teachers, etc.

Where do time words go? Is 你回来了吗昨天 okay?

Time words usually go before the verb phrase (or at the start):

你昨天回来了吗？ (correct)
昨天你回来了吗？ (also fine)
你回来了吗昨天？ (unnatural)