10 “fake-door” SaaS apps in 30 days, zero product code: how I’m using AI agents to validate before building

I’ve spent the last few months going deep on AI agents. They changed how fast I can move. Now I’m running an experiment to see how far I can push it: 10 SaaS ideas validated in 30 days using fake door landing pages. No product code until real people signal they want it.

I’m documenting everything here. The numbers, the failures, the pages that get zero clicks. If this works, I’ll share the playbook. If it flops, at least you’ll know what not to do.

Why fake doors?

A fake door is a landing page for a product that doesn’t exist yet. Real pricing, real CTA, waitlist on the other side. You’re testing demand before writing code. Skyler Talley explains the concept well here: https://youtu.be/jbVPygZbBYU

Hard rule I put in place after spending months (and years) building products barely anyone used: don’t build anything until I see real validation.

Why Japan?

I’m moving back to Tokyo in June. That prompted me to dig into the Japan SaaS market to see if there was an opportunity.

I scraped Shopify’s official Japan app collection (157 apps), read r/shopifyJapan threads, dug through <note.com> posts where Japanese merchants vent about their tools, and looked at what’s installed across ~42,000 Japan Shopify stores.

Same problems kept surfacing:

•	No AI customer support that speaks native Japanese. The English tools (Tidio, Gorgias, eesel) are machine-translated and the quality breaks trust.
•	LINE integrations exist but they’re messaging-only. Zero apps let you browse and buy inside LINE chat, the way Zoko does on WhatsApp.
•	157 Japan-tagged apps include zero SEO tools built for Japanese search. Hiragana, katakana, and kanji keyword variants matter.
•	No automation tool connects the actual Japanese B2B stack (Sansan + HubSpot + Chatwork + LINE).

US equivalents of all four are crushing it. Nothing built for Japan. That’s the bet.

The 5 fake doors (so far)

Each one has real pricing, a CTA, and a waitlist form. UTM tagged so I can track what brings traffic.

1. MoshiMoshi - AI customer support in native Japanese for LINE, email, and chat. [https://ai-jp-chatbot.vercel.app/]
2. Modoru - ManyChat for LINE. Abandoned cart recovery, broadcasts, AI chatbot.
3. Pochi - LINE Commerce. Browse and buy inside a LINE chat.
4. Mitsukaru - Japanese SEO audit built for hiragana/katakana/kanji and Yahoo Japan.
5. Karakuri - GTM automation for the Japan stack.

Some of these will die at week 4. That’s the point and why I'm using agents to build everything. Primally using Claude Code as handle ~80% dev including scaffolding for each landing page.

But I’m also using custom Claude agents for:

•	Competitive research: Scraping app stores, analyzing feature gaps, summarizing Japanese forum posts
•	Growth hacking: Generating <note.com> article drafts, identifying relevant communities, drafting outreach
•	Design: Product screenshots and mockups generated with Claude Code in under 2 hours
•	Async building: Claude dispatch lets me communicate with my server and keep building even when I’m away from my computer. I can review progress from my phone and it keeps shipping.

The speed difference is real. What would’ve taken me a week solo last year took 6 hours.

The stack (mostly free tier)

•	Claude + Claude Code for design and build
•	Vercel for hosting
•	Supabase for lead capture (free tier, Tokyo region)
•	Resend for signup notifications
•	GA4 + GTM for CTA click tracking
•	Linear to keep 10 apps in 30 days sane

Total cost: ~$15/month. Domains were $50 one-time.

Day 1 - Here’s what got done:

•	1 of 5 pages live (MoshiMoshi)
    •	Designed 5 product screenshots with claude design
•	Time from idea to deployed landing page: 6 hours
    •	4 more deploying this week

Kill criteria (week 8) If a page can’t hit these, I drop it:

•	CTA click rate > 4%
•	20+ email signups
•	40% of signups pick a paid tier

I’m not going to talk myself into building something nobody clicked.

I’ll post weekly numbers here. Right now my biggest gap is driving traffic to these pages to actually test demand.

If you have strategies for getting early eyeballs on landing pages, especially in the Japan market, I’d love to hear them. Or if you have questions about the agent workflow or anything else, drop a comment.