Case study · Own product

Chatt World

A group chat where every message arrives in each reader's language, so people who don't share a language can talk in the same group.

Visit chatt-world.com ↗
Role
Product, design and full stack development
Launched
September 2026
Platform
Web app, installable as a PWA
Stack
Fastify, WebSockets, PostgreSQL, React, Zustand
Chatt World landing page with a sample conversation in Portuguese and Japanese, translated into English for the reader
The public page of chatt-world.com: the original message on top, the translation underneath.

01 · The problem

Groups split by language

Mixed-language groups usually fall back to one shared language, or people copy messages into a translator and paste the answer back.

I wanted each person to write naturally in their own language and read everyone else in theirs, inside a chat that feels as complete as the apps they already use.

02 · What I built

A complete chat, translated for every reader

Conversation

  • Translation on arrival or on demand, using the author's language as a hint
  • Replies, mentions, edits, deletes and pinned messages
  • Reactions and five types of polls
  • Link previews protected against SSRF

Presence and alerts

  • Online status and typing indicators
  • Read receipts per message, also in private chats
  • Notification bell and Web Push as an installable PWA

Community

  • News feed with comments and likes
  • Friends and contacts with online status
  • Themes and chat backgrounds saved to the account

Global by design

  • Interface in each user's language
  • Right-to-left scripts supported
  • Public landing page and SEO in English

03 · Architecture

How it fits together

  1. Frontend

    React PWA

    Zustand state, service worker and Web Push

  2. Edge

    Cloudflare and Nginx

    Turnstile on sign-in and a strict content security policy

  3. API and realtime

    Fastify and WebSockets

    Messages, presence, translation and revocable sessions

  4. Data and media

    PostgreSQL

    Plus a separate processor that resizes photos and videos

04 · Engineering highlights

Built to be trusted

Security

Server-side sessions that users can revoke, single-use links to change a password, bot protection on sign-in and a strict content security policy.

Load testing

Load tests with k6 surfaced six failures under concurrency, and I fixed each of them.

Media pipeline

Photos and videos are resized by a separate processor, with thumbnails shown in the conversation.

Next

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