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

https://langfa.st/
3•eugenegusarov•4h ago
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.

Scanned Piano Rolls Database

http://www.pianorollmusic.org/rolldatabase.php
1•bookofjoe•34s ago•1 comments

Unpythonic: Supercharge your Python with parts of Lisp and Haskell

https://github.com/Technologicat/unpythonic
1•spapas82•2m ago•0 comments

I Solved the Century-Old Mystery of a Miraculous Shipwreck Survivor

https://thewalrus.ca/empress-of-ireland-survivor-mystery/
1•Thevet•3m ago•0 comments

Hope Catches a Tailwind

https://nautil.us/hope-catches-a-tailwind-1215966/
1•dnetesn•17m ago•0 comments

Does Anybody Know What Time Is?

https://nautil.us/does-anybody-really-know-what-time-is-1223272/
1•dnetesn•18m ago•0 comments

Rapid bursts of ageing are causing us to rethink how we grow old

https://www.newscientist.com/article/2485338-rapid-bursts-of-ageing-are-causing-a-total-rethink-of-how-we-grow-old/
1•rbanffy•20m ago•0 comments

Daniel Kleppner, Physicist Who Brought Atomic Clock Precision to GPS, Has Died

https://www.nytimes.com/2025/07/12/science/daniel-kleppner-dead.html
2•NaOH•21m ago•1 comments

Soya solving a critical pain point for founders manually finding your TA online

https://soya-platform.vercel.app/
1•Taikhoom10•29m ago•0 comments

Rivian R1S review: second time's the charm

https://www.theverge.com/electric-cars/689400/rivian-r1s-review-second-times-the-charm
2•breve•30m ago•0 comments

Fictitious Telephone Numbers

https://en.wikipedia.org/wiki/Fictitious_telephone_number
1•michaelgiba•32m ago•0 comments

Show HN: Brand Photography Images what present you in 10 mins with AI

https://www.gostudio.ai
1•gostudio_ai•38m ago•0 comments

A spacecraft carrying human remains and cannabis crashes into the ocean

https://phys.org/news/2025-07-spacecraft-human-cannabis-ocean.html
4•PaulHoule•41m ago•1 comments

Multisynapse optical network outperforms digital AI models

https://phys.org/news/2025-07-multisynapse-optical-network-outperforms-digital.html
1•elcid60•41m ago•0 comments

Easy dynamic dispatch using GLIBC Hardware Capabilities

https://www.kvr.at/posts/easy-dynamic-dispatch-using-GLIBC-hardware-capabilities/
3•Bogdanp•42m ago•0 comments

ML/AI Pipelines: The "So What" of Crypto Data Ecosystems

https://davanti-research.medium.com/machine-learning-the-so-what-of-crypto-data-ecosystems-db57137abea9
1•cascadius•43m ago•1 comments

She Wanted to Save the World from A.I. Then the Killings Started

https://www.nytimes.com/2025/07/06/business/ziz-lasota-zizians-rationalists.html
2•andrelaszlo•46m ago•1 comments

Internet Credit Union 2011-2015: RIP

https://blog.archive.org/2015/12/14/internet-credit-union-2011-2015-rip/
2•greyface-•50m ago•0 comments

Ask HN: Are there any tools for tracking GPU prices over time?

2•jepeake•55m ago•0 comments

GitHub – pollen-robotics/AmazingHand: Code and model to control the AH

https://github.com/pollen-robotics/AmazingHand
1•bilsbie•56m ago•0 comments

Start Budgeting Now

https://www.theatlantic.com/economy/archive/2025/07/trump-tariffs-trade-war-ongoing/683476/
6•cwwc•57m ago•0 comments

Computational understanding of Li-ion batteries (2016)

https://www.nature.com/articles/npjcompumats20162
1•sandwichsphinx•1h ago•0 comments

Why many American workers feel guilty about taking the vacation they've earned?

https://theconversation.com/why-do-so-many-american-workers-feel-guilty-about-taking-the-vacation-theyve-earned-254913
3•rntn•1h ago•2 comments

A universal interface connecting you to today's AI models

https://tenzorro.com/en/models
2•paulo20223•1h ago•0 comments

Show HN: Empromptu.ai – Agentic AI Building AI Apps

1•anaempromptu•1h ago•1 comments

Ask HN: Gift Ideas for 3 year old?

1•LecroJS•1h ago•7 comments

Tuitar – Learning Guitar with Ratatui and Embedded Rust (ESP32)

https://github.com/orhun/tuitar
1•weinzierl•1h ago•0 comments

China's Mini PC Production: How Tiny Computers Are Made [video]

https://www.youtube.com/watch?v=ohwI3V207Ts
3•Teever•1h ago•0 comments

Mathematical model reveals how humans store narrative memories with random trees

https://medicalxpress.com/news/2025-07-mathematical-reveals-humans-narrative-memories.html
2•mikhael•1h ago•0 comments

The UX Psychology Glossary

https://builtformars.com/ux-glossary
1•pipase•1h ago•0 comments

Wine 10.12 (Dev) – Run Windows Applications on Linux, BSD, Solaris and macOS

https://gitlab.winehq.org/wine/wine/-/releases/wine-10.12
1•neustradamus•1h ago•0 comments