1️⃣ Authentication & User Management APIs
Required for login, security, and identity


User registration


Login / Logout


JWT / OAuth token refresh


Password reset


Two-factor authentication


User profile (name, photo, status)


Presence status (online, away, busy, offline)


Organization / tenant management


Roles & permissions (admin, member, guest)



2️⃣ Contacts & Teams APIs
Core structure of Teams-like apps


Create / update / delete teams


Join / leave team


Team roles (owner, member)


Channels inside teams


Channel permissions


Private channels


Member list


Search users / teams



3️⃣ Messaging APIs (Most Important)
One-to-One Chat


Send message


Edit message


Delete message


Message delivery status


sent


delivered


read




Typing indicator


Message reactions (👍❤️😂)


Message replies / threads


Forward message


Group / Channel Chat


Send channel message


Threaded replies


Mentions (@user, @channel, @team)


Pin / unpin messages


Search messages


Message history pagination



4️⃣ Real-Time Communication APIs
Required for live experience


WebSocket / WebRTC signaling


Typing events


Online/offline presence updates


Read receipts


Live message sync


Reconnect handling



5️⃣ Media & File APIs


Upload files


Download files


File preview


Image compression


File permissions


Message attachments


Audio messages


Video messages


Storage quota tracking



6️⃣ Audio / Video Call APIs (Advanced)
This is complex & expensive


1-to-1 audio call


Group audio call


1-to-1 video call


Group video call


Screen sharing


Call signaling


Mute / unmute


Camera on/off


Call recording


Network quality detection


👉 Usually built with:


WebRTC


TURN / STUN servers



7️⃣ Notifications APIs


Push notifications (Firebase / APNs)


In-app notifications


Email notifications


Mention notifications


Missed call notifications


Message alerts preferences



8️⃣ Search APIs


Search users


Search messages


Search files


Search teams / channels



9️⃣ Status & Activity APIs


Custom status message


Away / Busy / Do Not Disturb


Last seen


Activity logs


Audit logs (admin)



🔟 Moderation & Safety APIs


Block / unblock users


Report messages


Content moderation


Message deletion by admin


User suspension


Data retention rules



1️⃣1️⃣ Settings APIs


Notification settings


Privacy settings


Language & timezone


Theme (dark / light)


Device management


Session management



1️⃣2️⃣ Analytics & Monitoring APIs


Message delivery metrics


Active users


Call quality stats


Error logs


Performance tracking



1️⃣3️⃣ Admin APIs


Organization management


User provisioning


Role management


Usage reports


Billing (if SaaS)



🔢 Rough API Count
Feature AreaApprox APIsAuth & Users15–20Teams & Channels15–20Messaging25–30Real-time10–15Media & Files10–15Audio/Video20–30Notifications8–10Search5–8Admin & Analytics10–15
👉 Total: ~140–180 APIs

🧠 Important Reality Check
Building Teams is not one app:


Backend microservices


Real-time servers


Media servers


Push notification services


Scalable databases


Message queues (Kafka / RabbitMQ)



🚀 Recommended Tech Stack (Example)


Backend: Node.js / Java / Go


Database: PostgreSQL + Redis


Real-time: WebSocket + WebRTC


Media: S3 / Azure Blob


Queue: Kafka / RabbitMQ


Auth: OAuth2 / OpenID


Push: Firebase + APNs



❓Next Step
If you want, I can:


Design full API schema (endpoint list)


Create database schema


Suggest MVP version (minimal APIs)


Help choose best architecture


Just tell me:
👉 MVP or full Teams-scale app?