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

Test, collaborate, version, and deploy prompts, from a single place, with PromptHub. Put an end to continuous copy and pasting and utilize variables to simplify prompt creation. Say goodbye to spreadsheets, and easily compare outputs side-by-side when tweaking prompts. Bring your datasets and test prompts at scale with batch testing. Make sure your prompts are consistent by testing with different models, variables, and parameters. Stream two conversations and test different models, system messages, or chat templates. Commit prompts, create branches, and collaborate seamlessly. We detect prompt changes, so you can focus on outputs. Review changes as a team, approve new versions, and keep everyone on the same page. Easily monitor requests, costs, and latencies. PromptHub makes it easy to test, version, and collaborate on prompts with your team. Our GitHub-style versioning and collaboration makes it easy to iterate your prompts with your team, and store them in one place.

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

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

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

Anyone looking for a tool to test their prompts to make sure they are consistent

Support

Phone Support Not Supported
24/7 Live Support Not Supported
Online Not Supported

Support

Phone Support Not Supported
24/7 Live Support Not Supported
Online Supported

API

Offers API Not Supported

API

Offers API Supported

Screenshots and Videos

No images available

Screenshots and Videos

Pricing

$60 one time
Free Version Not Supported
Free Trial Supported

Pricing

No information available.
Free Version Not Supported
Free Trial Not Supported

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

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 Not Supported
Webinars Not Supported
Live Online Not Supported
In Person Not Supported

Training

Documentation Supported
Webinars Not Supported
Live Online Supported
In Person Not Supported

Company Information

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

Company Information

PromptHub
www.prompthub.us

Alternatives

Alternatives

Categories

Prompt Engineering Supported

Categories

Integrations

Axis LMS Not Supported
Claude Not Supported
ElectroNeek Not Supported
GPT-3.5 Not Supported
Microsoft Azure Not Supported
OpenAI Not Supported
Zapier Not Supported

Integrations

Axis LMS Supported
Claude Supported
ElectroNeek Supported
GPT-3.5 Supported
Microsoft Azure Supported
OpenAI Supported
Zapier Supported
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