Products

Langfast

AI-native

Best LLM Playground for Prompt evaluations

langfa.st AI Models & Agents / Prompts, Evals & LLM Observability

AI Benchmark
Desktop
Mobile
Monthly visits
<5K
Sep 2026
Public revenue
Undisclosed
No public revenue evidence yet
Entry price
$49/mo
Higher than 67% of peersNiche median $21.595/mo
Creators
Eugene Gusarov
@eugene_gusarov· 9,569 followers
Launched
17mo ago
2025-06-29 · Est.

Traffic

Monthly visitsData through Sep 2026 · Oct 2026 pending

Marketing moves

Launches, search & content, referrals, promotions
X accounts@eugene_gusarov@yola

  • Launched on Show HN (50 pts · 17 comments)Launch

    I made a JSFiddle-style playground to test and share prompts fast — I built this out of frustration as I lead the development of AI features at Yola.com. Prompt testing should be simple and straightforward.…

    Jul 12, 2025 · 16mo agoLaunch page

  • Launched on IndiePageLaunch

    Langfast — Squeeze more out of that LLM

    Jun 29, 2025 · 17mo agoLaunch page

Third-party reviews & case dossiers

Acquisition breakdowns, engineer reviews & open-source metrics
Show HN
2025-07-12Source
Post excerpt:
I built this out of frustration as I lead the development of AI features at Yola.com. Prompt testing should be simple and straightforward. All I wanted was a simple way to test prompts with variables and jinja2 templates across different models, ideally somthing I could open during a call, run few tests, and share results with my team. But every tool I tried

Traffic sources

Sep 2026

Traffic breakdown

Channels

  • Direct40%
  • Organic Search35%
  • Referrals9%
  • Social7%
  • Other8%

Countries

No data yet

Search

Domain authority —Domain registered 2025-02-13

KeywordMonthly volume
farest top630
langfast160
felo llm playground10
langfast url—

Traffic data: Vaneform

Pricing

1-Year Pass
$49/once
Access valid for 12 months
Lifetime Access
$60/once

Trial: None · 2 paid tiers ($49–$60) · Observed 2026-11-04 · Pricing page

Entry price $49/mo, Higher than 67% of peers; “Prompts, Evals & LLM Observability” median is $21.595/mo.View pricing benchmark

Pages & changes

Tracked since 2026-09-15

Key pages

Weekly snapshots
langfa.st/ Snapshot 2026-11-04

Changes

No pricing, plan, or positioning changes detected since tracking started.

Questions & evidence

How much does Langfast cost?
1-Year Pass: $49/once; Lifetime Access: $60/once. Observed 2026-11-04. Check the source for current billing terms, usage limits and taxes.Source
How much website traffic does Langfast get?
Vaneform estimates <5K website visits in 2026-09. Visits can include repeat visits; this estimate measures web traffic separately from paying customers or revenue.Source
What is Langfast and what platforms does it support?
Langfast is catalogued under Prompts, Evals & LLM Observability: Best LLM Playground for Prompt evaluations. Supported platforms: Web.

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