About
Test, compare, and version prompts across top LLMs in seconds — no signup, no API keys required. Bring variables and conditional logic with Jinja2 smart templates, run side-by-side checks, share links with your team, and keep a history of what worked.
Key benefits
Zero friction: open and start testing instantly
Multi-model runs to spot regressions fast
Jinja2 variables for realistic, repeatable tests
One shared workspace for your product team
Linkable results and version history
Why choose it over alternatives
Most tools are heavy, pricey, and slow to set up. LangFast is lightweight, browser-first, and built for quick, real-world prompt evals—perfect for teams that need speed without the vendor lock-in or overhead.