Is Snapchat haram?

No, Snapchat is not haram in itself. It is a messaging and photo-sharing app, and like any app it depends on how you use it. The main risks are private chats with the opposite gender, immodest photos, wasted time and the false feeling that disappearing messages are not seen by anyone.

Disappearing messages are still recorded

Snapchat's big feature is that snaps vanish. That can tempt people to say or send things they would never post publicly. But in Islam, nothing disappears from the record:

مَّا يَلْفِظُ مِن قَوْلٍ إِلَّا لَدَيْهِ رَقِيبٌ عَتِيدٌ "not a word does a person utter without having a [vigilant] observer ready [to write it down]" Quran 50:18

A snap that deletes after ten seconds is still seen by Allah and recorded by the angels. Other people can also save it with a screenshot or a second phone. So a good rule is to send nothing you would be embarrassed to see later.

Chatting with the opposite gender

Snapchat is built around private one-to-one chats and "streaks", which can easily turn into daily flirting. Talking to people of the opposite gender for study, work or family reasons is fine. Long private chats with no purpose, late-night messages and sending selfies are where it goes wrong. The Prophet ﷺ said that the sins of the tongue and the eyes are real: the zina of the eyes is the look and the zina of the tongue is the talk (Sahih al-Bukhari 6243). See Can I chat with the opposite gender online as a Muslim?

Photos, filters and modesty

Never send private or revealing pictures. This is a serious sin, and a "temporary" photo can be saved and used against you.
Filters: fun filters are generally fine, but be careful with ones that change your face, beautify you in a misleading way or reveal too much.
Other people's snaps: don't screenshot or forward someone's private snap without permission. It breaks their trust.
Location: turn on Ghost Mode and limit who can see your map location, especially for women living alone.

Filters and edited photos raise their own questions. See Can I use beauty filters on my photos as a Muslim?

Saving other people's snaps is a separate trust issue. See Is it haram to screenshot private chats?

What you see: Spotlight and Discover

Snapchat's public feeds can show immodest or offensive content. Allah tells us not to follow what we have no knowledge of, because we will be asked about our hearing, sight and mind (Quran 17:36). Use the "show fewer like this" option, unfollow accounts that cause problems and avoid scrolling when you are alone and bored.

Time and streaks

Streaks make it hard to stop because you feel you will lose something. If you notice the app is taking up your day or making you late for prayer, set a time limit or delete it for a while. See How do I deal with social media addiction as a Muslim?

Key points

Snapchat is not haram in itself; what you do on it counts.
Disappearing messages are still recorded (Quran 50:18).
Avoid flirting, private photos and long pointless chats with the opposite gender.
Control your feed, your time and your location settings.

Tip: Before you send a snap, ask yourself: would I be fine with my parents, my imam and Allah seeing this? If not, don't send it.