ただ・ただし (tada / tadashi) — only… / provided that

Agreed — but one small thing: adding a condition or exception.

Formula (सूत्र ढाँचा)

S1。 + ただし／ただ、 + S2（条件・例外）。

Both words accept the previous point and add a small condition or exception.
「ただし」= "provided that" — formal, in rules and notices: 「参加は自由です。ただし、申し込みが必要です」= participation is free. However, you must register.
「ただ」= "only, one thing" — spoken, soft: 「いい店だよ。ただ、少し高い」= it's a good place. Just a bit pricey.
「ただ」alone also means "merely": 「ただ見ているだけ」.

N3Lesson 22's 「だが」/「しかし」contradict outright; ただ／ただし keep the main point and add a small caveat.

参加は自由です。ただし、申し込みが必要です。

さんかはじゆうです。ただし、もうしこみがひつようです。

Participation is free. However, you must register.

How it is built (कसरी बन्यो) The main point → ただし → a condition is added → the formal style of a notice.

いい店だよ。ただ、少し高い。

いいみせだよ。ただ、すこしたかい。

It's a good place. Just a bit pricey.

How it is built (कसरी बन्यो) The main point → ただ (conversational) → a small exception.

私はただ見ていただけです。

わたしはただみていただけです。

I was merely watching.

How it is built (कसरी बन्यो) ただ on its own = 'only' → paired with だけ.

Question: 1/3

On a rule notice, "provided that" — which?

💡 Hint: Formal.