Free Version
updated at: July 2025
Test, refine, and share AI prompts instantly
Langfa.st is a fast, no-signup prompt engineering playground that helps teams design, test, and optimize AI prompts with full control and minimal friction. Our platform is built for prompt engineers, developers, and product teams working with large language models (LLMs) who need to rapidly iterate and validate prompt behavior before going to production.
Category: Organization & Automation
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Additional Information
What is Langfa.st?
Langfa.st is a prompt testing and evaluation platform designed for teams building AI-powered products. It helps developers and product teams iterate faster, catch regressions, and ensure reliable AI behavior.
Features
- Prompt versioning with Git-style history and collaboration
- Structured testing for JSON/HTML outputs with schema validation
- Custom test cases with auto-scoring and diff comparisons
- Live feedback collection and review system
- Cost tracking and prompt performance analytics
- Integration with OpenAI and local LLMs
- Secure workspace with team-based roles and permissions
Use Cases
- Testing and improving prompts for production-ready AI features
- Comparing LLM outputs across model versions and edge cases
- Building prompt evaluation pipelines for product QA
- Sharing prompt snapshots with stakeholders for async review
- Conducting regression tests on complex AI workflows
Langfa.st's Pricing Plans
Langfa.st may change prices at any time. Here's our latest information:
Pro
One-time payment. No subscription
$60
- 50,000 extra requests included then $20 per 20,000 requests
- Full access to evaluations, workflows, and more coming soon
- Instant access to 50+ LLMs skip the setup — no API keys required
- Logs and history never expire
- Collaborate with your team members
- Ad-free
