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What is LangFast?

LangFast is a lightweight yet powerful prompt testing platform tailored for product teams, prompt engineers, and developers working extensively with large language models (LLMs). Offering instant, no-signup access to a fully customizable prompt playground, it simplifies the creation and testing of prompt templates using Jinja2 syntax. Users can see real-time raw outputs directly from the LLM without any API abstractions, enabling precise control and immediate feedback. By eliminating manual testing friction, LangFast allows teams to validate prompts, iterate rapidly, and collaborate more effectively on prompt development projects. Created by a team with a proven track record of scaling AI SaaS platforms to over 15 million users, the platform emphasizes control and scalability. LangFast supports seamless sharing of prompt templates, making teamwork intuitive and efficient. Its simple pay-as-you-go pricing model ensures cost predictability and accessibility for teams of all sizes. The platform’s clean and lightweight design means it can be integrated easily into existing workflows without overhead. LangFast empowers teams to accelerate innovation in prompt engineering while managing expenses effectively. This makes it an ideal choice for organizations looking to enhance their AI-driven product development with flexible and transparent prompt testing.

What is Agenta?

Agenta is a full-featured, open-source LLMOps platform designed to solve the core challenges AI teams face when building and maintaining large language model applications. Most teams rely on scattered prompts, ad-hoc experiments, and limited visibility into model behavior; Agenta eliminates this chaos by becoming a central hub for all prompt iterations, evaluations, traces, and collaboration. Its unified playground allows developers and product teams to compare prompts and models side-by-side, track version changes, and reuse real production failures as test cases. Through automated evaluation workflows—including LLM-as-a-judge, built-in evaluators, human feedback, and custom scoring—Agenta provides a scientific approach to validating prompts and model updates. The platform supports step-level evaluation, making it easier to diagnose where an agent’s reasoning breaks down instead of inspecting only the final output. Advanced observability tools trace every request, display error points, collect user feedback, and allow teams to annotate logs collaboratively. With one click, any trace can be turned into a long-term test, creating a continuous feedback loop that strengthens reliability over time. Agenta’s UI empowers domain experts to experiment with prompts without writing code, while APIs ensure developers can automate workflows and integrate deeply with their stack. Compatibility with LangChain, LlamaIndex, OpenAI, and any model provider ensures full flexibility without vendor lock-in. Altogether, Agenta accelerates the path from prototype to production, enabling teams to ship robust, well-tested LLM features and intelligent agents faster.

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Integrations Supported

Cohere
Falcon AI
Hugging Face
LangChain
Llama
Llama 2
Llama 3
Llama 3.1
Llama 3.2
Llama 3.3
OpenAI
Python

Integrations Supported

Cohere
Falcon AI
Hugging Face
LangChain
Llama
Llama 2
Llama 3
Llama 3.1
Llama 3.2
Llama 3.3
OpenAI
Python

API Availability

Has API

API Availability

Has API

Pricing Information

$60 one time
Free Trial Offered?
Free Version

Pricing Information

Free
Free Trial Offered?
Free Version

Supported Platforms

SaaS
Android
iPhone
iPad
Windows
Mac
On-Prem
Chromebook
Linux

Supported Platforms

SaaS
Android
iPhone
iPad
Windows
Mac
On-Prem
Chromebook
Linux

Customer Service / Support

Standard Support
24 Hour Support
Web-Based Support

Customer Service / Support

Standard Support
24 Hour Support
Web-Based Support

Training Options

Documentation Hub
Webinars
Online Training
On-Site Training

Training Options

Documentation Hub
Webinars
Online Training
On-Site Training

Company Facts

Organization Name

Langfa.st

Date Founded

2025

Company Location

United States

Company Website

langfa.st/new

Company Facts

Organization Name

Agenta

Date Founded

2023

Company Location

Germany

Company Website

agenta.ai/

Categories and Features

Categories and Features

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