んだって

1. 1Reports hearsay casually: "I heard that…" or "apparently…".Ex. 1
2. 2With rising intonation, asks the listener to confirm something the speaker has heard: "Is it true that…?"
3. 3Said insistently, it presses the speaker's own claim on a listener who doesn't accept it: "I'm telling you…!" (e.g. だから、私が見たんだって！)

Used in casual conversation with friends and family, mainly to share news or rumors picked up from others. Compared with the plain quoting って, the ん adds an explanatory nuance and presents the information as a notable fact. Compared with そうだ (hearsay) or ということだ, it is much more informal and conversational. In an insistent tone, it can also repeat the speaker's own claim to a listener who doubts it.

• そうだN4「そうだ」 also means 'I heard that...' and is interchangeable with 「んだって」, but it is neutral in register; the polite form 「そうです」 works in formal situations and often pairs with 「によると」. After nouns and な-adjectives, it becomes 「だそうだ」.
• ってN4「って」 can also mean 'called ~' or mark a topic; it is only similar to 「んだって」 when it expresses hearsay at the end of a sentence, where the two are often interchangeable. 「んだって」 carries the added explanatory nuance of 「ん」, making it sound more like sharing news.
• ということだN3「ということだ」 also expresses hearsay, but with an objective, somewhat written tone, and is common in news reports and notices; in casual chat, 「んだって」 sounds more natural. It also has a concluding 'in other words' meaning that 「んだって」 lacks.
• らしいN4When relaying hearsay, 「らしい」 is close to 「んだって」 and the two are often interchangeable in casual chat; however, 「らしい」 is neutral in register and relatively objective, and it can also express conjecture and function as a suffix (男らしい). When attached to a noun, say 「雨らしい」 directly, without adding 「な」.
• によると / によればN3「によると」 attaches to a noun to identify the source of the information and is neutral in register; it often pairs with 「そうだ」 or 「らしい」 at the end of the sentence and can also express inference based on materials. 「んだって」 is used at the end of a sentence, does not need to state the source, and is limited to casual speech.
• 〜と言うN4「と言う」 centers on the act of saying itself and can introduce direct or indirect quotations; it is neutral in register, and 「〜と言われている」 can also express what is generally said. 「んだって」 is casual spoken language focused on sharing something you heard, and with a rising intonation it can confirm with the listener.

Unlike そうだ (hearsay) and ということだ, which are neutral to formal and usable in writing, んだって is strictly casual speech; らしい can express the speaker's own inference as well as hearsay, and plain って quotes without the explanatory ん nuance. によると / によれば names the information source explicitly and is often combined with these endings, while 〜と言う simply reports someone's words as speech.