Show HN: I made a JSFiddle-style playground to test and share prompts fast

Hacker News (score: 19)
Found: July 12, 2025
ID: 272

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Show HN: I made a JSFiddle-style playground to test and share prompts fast I built this out of frustration as I lead the development of AI features at Yola.com.

Prompt testing should be simple and straightforward. All I wanted was a simple way to test prompts with variables and jinja2 templates across different models, ideally somthing I could open during a call, run few tests, and share results with my team. But every tool I tried hit me with a clunky UI, required login and API keys, or forced a lengthy setup process.

And that's not all.

Then came the pricing. The last quote I got for one of the tools on the market was $6,000/year for a team of 16 people in a use-it-or-loose-it way. For a tool we use maybe 2–3 times per sprint. That’s just ridiculous!

IMO, it should be something more like JSFiddle. A simple prompt playground that does not require you to signup, does not require API keys, and let's experiment instantly, i.e. you just enter a browser URL and start working. Like JSFiddle has. And mainly, something that costs me nothing if I'm or my team is not using it.

Eventually I gave up looking for solution and decided to build it by myself.

Here it is: https://langfa.st

Help me find what's wrong or missing or does not work from you perspctive.

P.S. I did not put any limits or restrictions yet, so test it wisely. Don't make me broke, please.

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