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

PromptCompose is a prompt infrastructure platform designed to bring software engineering rigor to prompt workflows. It offers version control for prompts, automatically tracking every change with deployment logs, side-by-side comparisons, and rollback capability, and integrates AB testing so multiple prompt variants can run concurrently, traffic can be split, performance tracked, and winners deployed confidently. Developers can integrate seamlessly via SDKs (JavaScript/TypeScript) or REST APIs so prompts and experiments can be part of production systems. Projects are organized in a hub structure so teams can manage resources (prompts, templates, variable groups, tests) per project, with proper isolation and collaboration. PromptCompose supports prompt blueprints (templates) and variable groups so prompts can be parameterized with dynamic inputs in a consistent, reusable way. The editor includes features like syntax highlighting, autocomplete for variables, and error detection.

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

AI engineering teams and product builders requiring a solution to manage, test, and deploy prompts reliably

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

PromptCompose
Founded: 2025
Jordan
promptcompose.ai/

Alternatives

Alternatives

Categories

Prompt Engineering Supported

Categories

AI Productivity Supported

Integrations

JavaScript Not Supported
Python Not Supported
TypeScript Not Supported

Integrations

JavaScript Supported
Python Supported
TypeScript Supported
Claim LangFast and update features and information
Claim LangFast and update features and information
Claim PromptCompose and update features and information
Claim PromptCompose and update features and information