LangFastLangfa.st
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OpenUIThesys
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Related Products
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About
LangFast is a lightweight prompt testing platform designed for product teams, prompt engineers, and developers working with LLMs. It offers instant access to a customizable prompt playground—no signup required. Users can build, test, and share prompt templates using Jinja2 syntax with real-time raw outputs directly from the LLM, without any API abstractions.
LangFast eliminates the friction of manual testing by letting teams validate prompts, iterate faster, and collaborate more effectively. Built by a team with experience scaling AI SaaS to 15M+ users, LangFast gives you full control over the prompt development process—while keeping costs predictable through a simple pay-as-you-go model.
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About
OpenUI is an open-source (MIT) generative UI framework for AI agents. Instead of plain text, your agent writes OpenUI Lang, a compact, streaming-first language, and OpenUI renders it progressively as real UI: charts, tables, forms, cards and layouts. Rendering is safe by default: the model can only use components you register and no generated code is executed, so your design system stays in control. A framework-agnostic core powers first-party runtimes for React, Vue, Svelte and Angular, with ready-made chat interfaces and integrations for LangChain/LangGraph, the Vercel AI SDK, Mastra, Google ADK, assistant-ui, CopilotKit, AG-UI and A2UI. In its published benchmark, OpenUI Lang uses about half the tokens of equivalent JSON UI formats, so interfaces stream faster and cost less.
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Platforms Supported
Windows
Not Supported
Mac
Not Supported
Linux
Not Supported
Cloud
Supported
On-Premises
Not Supported
iPhone
Not Supported
iPad
Not Supported
Android
Not Supported
Chromebook
Not Supported
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Platforms Supported
Windows
Supported
Mac
Supported
Linux
Supported
Cloud
Supported
On-Premises
Supported
iPhone
Supported
iPad
Supported
Android
Supported
Chromebook
Supported
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Audience
Product teams, software engineers, prompt engineers, AI developers, ML researchers, startup founders, and technical writers working on AI-powered features or language model integrations.
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Audience
Developers building AI agents, copilots and chat apps who want agents to answer with interactive UI instead of text
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Support
Phone Support
Not Supported
24/7 Live Support
Not Supported
Online
Not Supported
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Support
Phone Support
Not Supported
24/7 Live Support
Not Supported
Online
Supported
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API
Offers API
Not Supported
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API
Offers API
Not Supported
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Screenshots and VideosNo images available
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Screenshots and VideosNo images available
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Pricing
$60 one time
Free Version
Not Supported
Free Trial
Supported
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Pricing
Free
Free Version
Supported
Free Trial
Not Supported
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Reviews/
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Reviews/
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Training
Documentation
Not Supported
Webinars
Not Supported
Live Online
Not Supported
In Person
Not Supported
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Training
Documentation
Supported
Webinars
Not Supported
Live Online
Not Supported
In Person
Not Supported
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Company InformationLangfa.st
Founded: 2025
United States
langfa.st/new
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Company InformationThesys
Founded: 2024
United States
www.openui.com
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Alternatives |
Alternatives |
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Categories |
Categories |
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Integrations
A2UI
Not Supported
AG-UI
Not Supported
Agent Development Kit (ADK)
Not Supported
CopilotKit
Not Supported
LangChain
Not Supported
LangGraph
Not Supported
Mastra AI
Not Supported
Vercel AI SDK
Not Supported
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Integrations
A2UI
Supported
AG-UI
Supported
Agent Development Kit (ADK)
Supported
CopilotKit
Supported
LangChain
Supported
LangGraph
Supported
Mastra AI
Supported
Vercel AI SDK
Supported
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