Hey everyone! 👋 Glad to join the community.

A while ago at work, we faced a lot of frustration trying to test the prompts we were developing for AI features at Yola.com. Most prompt testing tools out there are overcomplicated. You need to sign up, bring your own API keys, deal with clunky UIs, or pay $6,000/year just to run a few prompt tests with your team.

As someone leading AI feature development at Yola.com, I got tired of all that.
I just needed something simple — a place to quickly test prompts (with variables), compare outputs across models, and share results with the team. Something I could open during a call, run a few tests, and close. No setup, no friction.

So I built Langfa.st — a JSFiddle-style playground for AI prompts.
No login. No API key. 50+ models. Jinja2 templating. Variables. Instant results.
If you’re not using it — it costs you nothing.