Multi-Tab Sync Chat
A working demonstration of the BroadcastChannel API: open the page in several tabs, type in one, and the message appears in the rest instantly - no server, no backend. Same-origin and same-browser only, so nothing leaves your machine. Useful for seeing cross-tab state sync before building it yourself. Imported Claude artifact. Source: https://github.com/simonw/tools (broadcast-channel-chat.html, Apache-2.0).
Name your fork
This clones the app's prompt and source into your account as a new unlisted app. You can edit and publish it from your dashboard.
Details
View source prompt + release files — fork-enabled apps share their full source
System prompt (SKILL.md)
---
name: multi-tab-chat
description: A working demonstration of the BroadcastChannel API - type in one browser tab and watch it appear instantly in every other tab.
metadata:
tags:
- artifact-import
- dev-tools
source_url: https://tools.simonwillison.net/broadcast-channel-chat
github_repo_url: https://github.com/simonw/tools
---
# Multi-Tab Sync Chat
An imported Claude artifact demonstrating the BroadcastChannel API. Open this
page in two or more tabs, type in any of them, and the message appears in the
others immediately - each tab numbered, synced messages marked with which tab
they came from.
There is no server involved: BroadcastChannel is a same-origin, same-browser
message bus, so nothing you type leaves your machine and nobody else's tabs can
see it. That is also the honest limit of the demo - it is not a chat room, it is
a way to see cross-tab state sync working, which is the useful part when you are
deciding how to keep a multi-tab app consistent.
Message text is HTML-escaped before rendering, and browsers without
BroadcastChannel get a clear unsupported notice rather than a dead page.
No model is called and nothing is metered.
Release files (files)
Every public app is built from a security-scanned skill and must pass a clean scan — skill and frontend — before it can be listed. Have a skill of your own? Turn it into an app — or read the step-by-step walkthrough.