んだってI heard that, He or She said that

って (a contracted form of と) is a casual quoting particle used to mark direct or indirect speech, thoughts, feelings, or to introduce a topic. んだって, which combines って with the explanatory ん・の, is used to express 'I heard' or 'He/she/they said.' While って can follow any word, んだって requires な before な-Adjectives or nouns.

んだって and らしい ① both convey information from another source, but with different nuances and levels of formality. らしい ① suggests hearsay with a nuance of certainty, indicating the speaker believes it to be true, e.g. 'Apparently it's (A).'. In contrast, んだって is highly casual and includes an explanatory nuance, similar to 'He/she/they said/say (A), you know.'.

Both ときいた and んだって express hearsay, but with different nuances and formality. ときいた means 'I heard (A).' and conveys information directly heard by the speaker, e.g. 高いときいた ('I heard it was expensive.'). In contrast, んだって is casual and adds an explanatory nuance, like 'They say (A).' or 'I heard that (A).', e.g. 高いんだって ('They say it's expensive, you know.').