LangFast

LangFast

Langfa.st
+
+

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About

Iterate quickly and ship confidently. Confidently ship by evaluating your prompts with a suite of evals like context recall, llm-rubric (LLM as a judge), latency, and more. Let us handle intelligent caching and complex implementations to save you time and money. Quickly iterate on your prompts in a collaborative playground that supports all the major providers, variables, automatic versioning, and more. Easily build datasets from real data using Logs, upload your own as a CSV, or collaboratively build and edit within your Adaline workspace. Track usage, latency, and other metrics to monitor the health of your LLMs and the performance of your prompts using our APIs. Continuously evaluate your completions in production, see how your users are using your prompts, and create datasets by sending logs using our APIs. The single platform to iterate, evaluate, and monitor LLMs. Easily rollbacks if your performance regresses in production, and see how your team iterated the prompt.

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.

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

Anyone in need of a solution to iterate, evaluate, and monitor LLMs

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.

Support

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

Support

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

API

Offers API Supported

API

Offers API Not Supported

Screenshots and Videos

Screenshots and Videos

No images available

Pricing

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

Pricing

$60 one time
Free Version Not Supported
Free Trial 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:

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

Training

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

Company Information

Adaline
www.adaline.ai/

Company Information

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

Alternatives

Alternatives

Categories

Prompt Engineering Supported

Categories

Prompt Engineering Supported

Integrations

Google Sheets Supported
Microsoft Excel Supported

Integrations

Google Sheets Not Supported
Microsoft Excel Not Supported
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