LangFast

LangFast

Langfa.st
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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.

About

Develop and version control your prompts. Auto-generated API to retrieve prompts. Automatically run end-to-end LLM testing before making updates to your prompts on production. Let your industry specialists and engineers collaborate on the same platform. Let your industry specialists and prompt engineers test and iterate on the same platform without any programming knowledge. With our testing suite, you can create and run unlimited test cases to ensure the quality of your your your your your prompt. Check for hallucinations, issues, edge cases, and more. Our suite is the most complex of prompts. Use Git-like features to manage your prompts. Create a repository for each project, and create multiple branches to iterate on your prompts. Commit your changes and test them in a separate environment. Easily revert back to a previous version. With our real-time APIs, one single click, and your prompt is updated and live.

Platforms Supported

Windows
Mac
Linux
Cloud
On-Premises
iPhone
iPad
Android
Chromebook

Platforms Supported

Windows
Mac
Linux
Cloud
On-Premises
iPhone
iPad
Android
Chromebook

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.

Audience

AI engineers and anyone requiring a tool to build their CI/CD pipeline for AI prompts

Support

Phone Support
24/7 Live Support
Online

Support

Phone Support
24/7 Live Support
Online

API

Offers API

API

Offers API

Screenshots and Videos

No images available

Screenshots and Videos

Pricing

$60 one time
Free Version
Free Trial

Pricing

Free
Free Version
Free Trial

Reviews/Ratings

Overall 0.0 / 5
ease 0.0 / 5
features 0.0 / 5
design 0.0 / 5
support 0.0 / 5

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Reviews/Ratings

Overall 0.0 / 5
ease 0.0 / 5
features 0.0 / 5
design 0.0 / 5
support 0.0 / 5

This software hasn't been reviewed yet. Be the first to provide a review:

Review this Software

Training

Documentation
Webinars
Live Online
In Person

Training

Documentation
Webinars
Live Online
In Person

Company Information

Langfa.st
Founded: 2025
United States
langfa.st/new

Company Information

Prompteams
www.prompteams.com

Alternatives

Alternatives

Vellum AI

Vellum AI

Vellum

Categories

Categories

Integrations

No info available.

Integrations

No info available.
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