LangFastLangfa.st
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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
Introducing Narrow AI: Take the Engineer out of Prompt Engineering
Narrow AI autonomously writes, monitors, and optimizes prompts for any model - so you can ship AI features 10x faster at a fraction of the cost.
Maximize quality while minimizing costs
- Reduce AI spend by 95% with cheaper models
- Improve accuracy through Automated Prompt Optimization
- Achieve faster responses with lower latency models
Test new models in minutes, not weeks
- Easily compare prompt performance across LLMs
- Get cost and latency benchmarks for each model
- Deploy on the optimal model for your use case
Ship LLM features 10x faster
- Automatically generate expert-level prompts
- Adapt prompts to new models as they are released
- Optimize prompts for quality, cost and speed
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Platforms Supported
Windows
Mac
Linux
Cloud
On-Premises
iPhone
iPad
Android
Chromebook
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Platforms Supported
Windows
Mac
Linux
Cloud
On-Premises
iPhone
iPad
Android
Chromebook
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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
AI Startups, AI Developers, AI Founders, CTOs
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Support
Phone Support
24/7 Live Support
Online
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Support
Phone Support
24/7 Live Support
Online
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API
Offers API
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API
Offers API
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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
Free Trial
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Pricing
$500/month/team
Free Version
Free Trial
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Reviews/
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Reviews/
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Training
Documentation
Webinars
Live Online
In Person
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Training
Documentation
Webinars
Live Online
In Person
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Company InformationLangfa.st
Founded: 2025
United States
langfa.st/new
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Company InformationNarrow AI
Founded: 2024
United States
www.getnarrow.ai/
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Categories |
Categories |
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Integrations
GPT-4
GPT-4o
Llama 3.1
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