When I launched fknjsn.com — a local-first JSON comparison tool with no backend, no tracking, and a name your mum wouldn't approve of — I expected maybe twelve people to use it. Mostly me. Possibly my future self debugging the same API at 2am.
Instead, something unexpected happened. People from 15 countries started showing up.
Australia. The United States. The Netherlands. India. The UK. Poland. Germany. Spain. Pakistan. Guatemala. Hong Kong. Romania. Italy. Singapore. Saudi Arabia.
A truly global coalition of developers who are tired of pasting secrets into online formatters and hoping for the best.
And they all wanted the same thing.
"Let me copy the damn JSON"
Fair enough.
You could paste JSON in. You could format it. You could filter it. You could compare two payloads side by side. You could do all of this without a single byte leaving your browser. But when you wanted to actually take the result with you? You were selecting text like an animal.
Developers from across four continents were independently arriving at the same frustration, which honestly felt like a UN resolution against bad clipboard UX.
What's new
You can now copy filtered and formatted JSON with one click. That's it. That's the feature.
- Filter a nested payload down to the three keys you care about → copy
- Format some minified nightmare into something readable → copy
- Compare two responses, find the diff, grab the clean version → copy
It respects whatever state your JSON is in. If you've filtered it, you get the filtered result. If you've formatted it, you get the formatted output. Not the original. Not some re-serialized approximation. What you see is what you copy.
paste → format → filter → copy → done → go outside
Revolutionary stuff. Also known as "finishing the job."
Still no backend
Same architecture as before. Your JSON never leaves your browser. No server. No database. No shareable URLs that attackers can scrape. No save feature that quietly publishes your AWS credentials to a guessable endpoint for five years.
Just localStorage, a copy button, and the basic respect of not uploading your data to someone else's computer.
Try it
fknjsn.com — paste, format, filter, copy. Everything stays local.
The source is still a single HTML file. View source still works. The trust model is still "don't trust me, verify it yourself."
Now with 100% more clipboard support, by popular international demand.
The name is pronounced exactly how you think it is. And apparently, developers in 15 countries all think the same thing.
Top comments (1)
Love this update — it’s honestly refreshing to see someone actually listen to users and ship the one feature everyone was silently screaming about. The “what you see is what you copy” approach is such a small detail, but it makes the tool feel complete and intentional instead of half-finished. Also, keeping everything local-first with zero backend is a huge trust win in a world where people casually paste secrets into random formatters.
I really like the philosophy behind this project — simple, focused, and respectful of developers’ data. Maybe in the future you could add optional keyboard shortcuts for copy to make the workflow even faster for power users. Either way, this is the kind of tooling that feels built by someone who actually debugs APIs at 2am. Definitely bookmarking it and looking forward to what you improve next.