whereismyai
Langfa.st
Langfa.st is an LLM playground that allows product teams to test, compare, and debug prompt templates across multiple AI models using their own API keys.
LangFast serves as a centralized environment for evaluating LLM prompts. Users input their own API keys to run tests, stream responses, and compare output across models side-by-side. The platform supports features like Jinja2 templating, dynamic variables, and function calling. It enables teams to save chats, share links, and maintain version control during the prototyping phase. The tool is designed to assist product teams in validating AI features and debugging prompt results before shipping to production.
Langfa.st at a glance
- Best for: Software engineer, Product manager
- Runs on: Web, API
- Pricing: 1-Year Pass: $49 one-time; Lifetime Access: $60 one-time
- Released: July 2025
- Category: AI coding tool
- Website: langfa.st
Key features
- Side-by-side model comparison
- Jinja2 template support
- Dynamic variables
- Function calling support
- Version control for prompts
- Role-based permissions
- Token and cost statistics tracking
Use it for
- Testing and validating prompt templates
- Comparing LLM outputs for specific prompts
- Debugging AI prompt performance issues
- Collaborating on prompt engineering projects
Alternatives to Langfa.st
- LangChain4j — Integrates LLMs and vector stores directly into Java applications.
- Langfuse — It connects tracing, prompt management, and evaluations in one open platform.
- LMQL — It enables modularized, constraint-based prompting with portable code.
- 16x Prompt — Manage code context and compare multiple LLM responses side-by-side easily.
- WebLLM — Runs high-performance language models directly inside web browsers.
- Langroid — Simplifies multi-agent orchestration and app development with intuitive abstractions.
- LangSmith — Step-by-step traces and evals that show what an agent actually did
- Applitools — Eliminates false positives and verifies AI-generated code with visual precision.
- LLM CLI — It enables command-line interaction with remote APIs and local machine models.
- LangChain — Compose exactly the agent your use case needs from model, tools, prompt, and middleware.
- LiteLLM — One OpenAI-format API for 100+ LLM providers
- LightLLM — It delivers high-speed inference and serving performance for large language models.
All Langfa.st alternatives