Get Started
Reaction Sync is a browser extension. Install it once, and it keeps a reaction video and the source content playing in step. Setting it up takes about a minute.
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Designed for Chrome and Chromium-based browsers. We don't support Firefox or Safari right now.
Why isn't this on the Chrome Web Store?
We're not listed there yet. Store review takes time, and we'd rather ship to the people who want this now than wait. Installing directly takes about a minute and gives you exactly the same extension.
Installation on Chrome
Chrome is the recommended browser — it's what we build and test on.
- Extract the zip to a folder you'll keep. Not your Downloads folder — see the note below.
- Open a new tab and go to
chrome://extensions. - Turn on Developer mode with the toggle in the top-right corner.
- Click Load unpacked and choose the folder you extracted.
- Reaction Sync appears in the list. Click the puzzle-piece icon in your toolbar and pin it, so it's one click away.
chrome://extensions.
About the warning you see when you enable Developer mode.
It is a real security mechanism: Developer mode lets you load any extension from any folder, so Chrome tells you so. We are a registered company — Dwarka Point Technologies Private Ltd — with a published privacy policy. Chrome will also show you exactly what this extension can reach: click Details on the Reaction Sync card and read Site access. It lists the video sites we sync and nothing else.
Keep the folder where it is.
Chrome loads the extension from that folder every time it starts — it doesn't copy it anywhere. If you move the folder, rename it, or delete it while tidying up your Downloads, the extension stops working. Put it somewhere you won't touch by accident, like a folder in your Documents.
Installation on other Chromium-based browsers
Edge, Brave, Opera, Vivaldi and Arc all run Chrome extensions, and Reaction Sync works the same way on them. The steps are identical — only the address of the extensions page differs.
edge://extensions
The Developer mode toggle sits in a different corner depending on the browser, but it's on that same page.
We develop and test on Chrome. These browsers share the same extension engine, so things generally behave identically — but if you hit something odd, tell us and mention which browser.
Firefox, Safari and other non-Chromium browsers
Not supported at the moment. Both use a different extension system, so it's a real piece of work rather than a repackage — we'll do it if enough people ask. If you're on one of them, let us know and we'll count you.
Your first pairing
The easiest way to start is with a sync link — someone has already lined the two videos up, so there's nothing to set up yourself.
You'll need to sign in first.
The first time you open the extension it asks you to sign in with your Google account. That's a one-off — after that it remembers you.
- Open both videos. What you're watching in one tab, the reaction in another. Press play on both and leave them playing while you set up.
- Open the sync link that came with the reaction. Reaction Sync picks it up and asks which two tabs to use.
- Pick your two tabs and start. The alignment comes from the link — you don't have to mark anything.
- Watch. Pause, seek or rewind on either video and the other follows.
No sync link for what you're watching? You can line the two up yourself and save it as one — the FAQ covers that, along with anything else about using the extension.
Updating the extension
When a new version is out, the extension tells you inside the popup.
- Download the new zip from this page.
- Extract it over the same folder, replacing the old files.
- Go to
chrome://extensionsand click the reload icon on the Reaction Sync card.
Replacing the folder in place matters — if you remove the extension and add it back instead, you'll be signed out and have to sign in again.