Karlo Percinic

Solo founder building LandlordHub — rental management for small self-managing landlords — and BreakWatch, an early-stage monitor that warns you before third-party API deprecations break your product. Zagreb 🇭🇷

Building

Two products, building in public — LandlordHub (live) and BreakWatch (validating).

LandlordHub
All-in-one rental management for self-managing landlords with a few units — rent tracking, tenant portal, maintenance requests and document storage in one simple app. Not built for agencies. Built for the landlord still running everything in spreadsheets and WhatsApp. Free for your first property, €9/mo for unlimited.
Live€0/mo
BreakWatch
BreakWatch watches the changelogs and deprecation notices of the third-party APIs your product depends on (Stripe, LLM providers, payment/auth/email vendors) and alerts you before a breaking change ships — so you fix it on your schedule, not during an outage. Currently in staging, validating with early users.
Building

Recent activity

My waitlist wasn't converting — so I deleted it and built the actual product

We scanned 50,000 domains. Your cold email list is really four systems.

How to rank #1 on ChatGPT?

We scanned 50,000 domains. Your cold email list is really four systems.

2 weeks of fixing my Shopify App Store listing + building SEO content — installs haven't moved (yet)

We scanned 50,000 domains. Your cold email list is really four systems.

2 weeks of fixing my Shopify App Store listing + building SEO content — installs haven't moved (yet)

We shut down a product years ago. This year we rebuilt it and the first paying customer came from the old user list.

My new product has a public kill condition: 20 leads or it dies

Bigger creators, worse results

My client's site started getting cited in AI after 2 weeks (just from Reddit)

Launching on Product Hunt today, but I need honest feedback more than upvotes.