Deep dive
Decide the encryption model first
Every messenger makes a basic choice. Cloud chats keep messages encrypted in transit and at rest on your servers, with keys you manage; that enables instant multi-device sync, server-side search and huge groups. End-to-end encrypted chats keep keys only on devices; the server cannot read content, which protects users but makes sync, backups and moderation harder.
Some messengers offer both: cloud chats by default and optional secret chats with device-only keys. If you choose end-to-end encryption, use audited protocols such as the Signal protocol or Messaging Layer Security (MLS, RFC 9420) for groups, never a home-grown scheme. Make the choice in discovery, because it shapes the data model, backup design and moderation approach.
How delivery and sync work
Each device keeps a persistent connection to the messaging service. Every change to a chat, whether a new message, an edit, a delete or a read receipt, gets a sequence number. When a device reconnects, it asks for everything after the last sequence it saw, so a phone that was offline for a week catches up in one request. Push notifications wake devices that are not connected.
Large groups and channels use different delivery paths: rather than pushing a message to every member's queue, the server stores it once and members pull it when they open the chat, with notifications sent in batches. That keeps a channel with millions of subscribers affordable.
- Give every update a sequence number per account or chat and make delivery idempotent.
- Store messages once per chat, not once per member.
- Batch and rate-limit notifications for large groups and channels.
Bots and mini apps turn chat into a platform
A bot API lets developers build services that users talk to: customer support, ordering, alerts, games and tools. Bots receive updates through webhooks or long polling and reply with messages, buttons and menus. Mini apps go further, running web interfaces inside the chat with access to the user's identity when they allow it.
Platform features need platform discipline: API keys, rate limits, documentation, a review process for public bots, clear data rules and payment flows that follow app store policies. Our AI chatbot development team builds bots for these platforms, and the same experience applies when you build your own.
Bots are also where AI fits most naturally. An assistant bot that summarises long group discussions, answers questions from a channel's archive or drafts replies can be built on language model APIs without changing the core messenger. Keep it opt-in, explain what data the bot sees, and never send end-to-end encrypted content to a server-side model without the user's explicit action.
Moderation for channels and large groups
Private chats are private, but public channels and large groups are publishing tools. They need reporting, takedowns for illegal content, spam and scam detection, channel verification and cooperation processes for valid legal requests. The EU Digital Services Act, the UK Online Safety Act and India's IT Rules all apply to public spaces on messaging platforms.
Design the line between private and public carefully. Public content can be scanned and moderated like any social platform; private chats rely on user reports and metadata signals. Publish your approach in plain language so users and regulators understand it.
Running costs
Messaging is cheap per message and expensive in total. The main lines are connection servers, message storage that never stops growing, media storage and CDN delivery for large files, push notifications, TURN relay bandwidth for calls and SMS for sign-up codes. Generous file size limits are a deliberate cost decision.
Maintenance is roughly 15-20% of the build cost per year, plus the infrastructure above. Our cloud services team usually models cost per active user before launch so pricing for premium tiers is grounded in real numbers.