Building a Timezone Converter Chrome Extension: Convert Time Case Study

#javascript #productivity #showdev #extensions

There are over 400 timezones. I built a Chrome extension that handles all of them on hover. Here's what I learned.

Key Metrics

Metric	Value
Installs	267
Timezones Supported	400+
User Action Required	1 hover
Time Saved	∞

The Problem

I saw many people in reddit forums, constantly tripping over timezone math. Every call, every deadline, every "let's sync at 3pm" - which 3pm? Mine or yours?
There are over 400 when you factor in half-hour offsets, DST variations, and regional quirks. With remote work now the norm, this affects everyone from sales teams booking demos to recruiters scheduling interviews.

So I set out to stop people googling "what time is 2pm PST in GMT+7" five times a day.

The Solution

Convert Time is a Chrome extension that does one thing: it finds times on the webpage you're looking at and tells you what they are in your timezone. Hover over a detected time, get a tooltip.

Key Features

Automatic detection - picks up formats like "2 PM PST", "14:00 CET", "5:30pm (GMT+7)", and ISO datetime strings, then underlines them inline
Hover-to-convert - one hover gives you the conversion in a tooltip, no clicks needed
Zero data collection - runs entirely in the browser, nothing leaves your machine

Technical Challenges

Timezone Parsing

I didn't realise there were so many timezones. Building the parser to catch all the different ways people write times - "2pm EST", "14:00 CET", "5:30 PM Pacific", "2025-08-07 08:02:46 GMT+0000" - without false positives on random numbers was a proper challenge. I built this with Claude and got a massive amount done super quickly, but it's been an ongoing process of refinement.

The Edge Cases Keep Coming

I dogfood this extension daily, which means I keep finding things to fix. Some highlights from the changelog:

EST vs EDT ambiguity - Americans say "EST" when they sometimes mean "EDT", so I had to treat it as a double timezone showing both UTC-5 and UTC-4 conversions unless explicitly stated
False positives everywhere - +8 UTC was incorrectly matching 8 UTC. 5 with office was matching 5 wit. Had to add word boundary checks and context validation
Editable text areas - The extension was interfering with text inputs and X/Threads post drafting. Had to add filtering to respect user input areas
GMT+N offset parsing - 1:00 AM (GMT+7) was being parsed as GMT+0 because the regex wasn't capturing the numeric offset properly

Every fix makes it more robust, but timezone handling is one of those problems that never really feels fully solved.

The Results

Growth was slow - it took about 5 months before I started getting any real traction. Now it's pulling in 1-2 installs a day organically through the Chrome Web Store. I think they're mainly coming from my reddit posts and google search.

No reviews yet, but 267 total installs and growing steadily!

What I Learned

There are way more timezones than you think. 400+. And every single one of them has formatting quirks, DST rules, and abbreviation conflicts. I went in thinking this would be straightforward. It wasn't.
Dogfooding is the best QA. using the extension myself every day across different sites and timezones surfaced bugs I never would have caught otherwise. False positives in random text, EST/EDT confusion - all found by just using the thing.
Slow growth is still growth. five months of near-nothing, then steady 1-2 installs a day. If the problem is real and your solution works, people find it eventually.