Chat app development: the features a messaging app needs

Accounts, sync, voice notes, groups, backups, encryption, media, push notifications and moderation: what each chat feature involves and which store rules apply.

Messaging looks simple from the outside: type, send, read. Behind it sit real-time servers, offline sync, storage for years of history, and rules from Apple and Google about how people may be contacted and protected. This list walks through the features a chat app usually needs and what each one costs in effort and obligations.

Accounts and sign-in

Users need an identity: a phone number, an email address or a sign-in from another service. Apple’s App Review Guidelines add a requirement that is easy to miss: if an app lets people create an account, it must also let them delete it from within the app (guideline 5.1.1(v)). Design the deletion flow, and what happens to that person’s messages, from the start.

Sync across devices

People expect a conversation to look the same on their phone, tablet and laptop, and to catch up after being offline. That means a server that keeps the authoritative history, a clear rule for message order, and handling for messages sent while offline. Expect sync to take a large share of the engineering estimate.

Voice messages and media sharing

Recording voice notes needs microphone access; sending photos needs camera or photo library access. Google’s core app quality guidelines ask apps to request only the permissions they need, at the moment a feature is used rather than at startup, to explain why, and to keep working if the user says no. Media also needs storage, compression and limits on file size.

Groups and broadcasts

Group chats and one-to-many broadcast lists bring their own questions: who can add members, who can post, how large a group may grow, and how admins remove someone. Each answer is a screen, a permission rule and a server check.

Backups and history

Users expect to keep their history when they change phones. Decide where backups live, how they are encrypted, and how long you keep messages. Under the PDPA’s retention limitation obligation, personal data should not be kept once it is no longer needed for a business or legal purpose, so “forever” needs a reason.

Encryption and security

Messages must be protected in transit and at rest. OWASP’s MASVS is a useful checklist: its control groups cover storage of sensitive data on the device, cryptography, authentication, network communication and privacy. Decide early whether messages are end-to-end encrypted, because that choice changes how search, backups, moderation and multi-device sync can work.

Push notifications

A chat app is useless if people do not know a message arrived. Services such as Firebase Cloud Messaging deliver notifications to iOS, Android and web apps, and can tell an app that new messages are waiting to sync. Apple’s guideline 4.5.4 sets limits: the app must work without push notifications, notifications should not carry sensitive personal information, and marketing messages need explicit opt-in in the app and a way to opt out.

Reporting, blocking and moderation

Any app where users send content to each other falls under Apple’s guideline 1.2 on user-generated content. It requires a way to filter objectionable material, a way to report offensive content with timely responses, the ability to block abusive users, and published contact information. Budget for the tools and for the people who will act on reports.

Personal data overall

Chat apps hold phone numbers, contact lists, messages and media: personal data on every screen. The PDPC’s list of obligations applies throughout, including consent, protection and breach notification. For the wider process of building an app, see the overview guide.