Costart Projects — solo founder & operator
I build the products, and I do the growth maths behind them.
I'm Robert Costart — a solo operator who builds products end to end and helps growth teams scale them. Over the last decade I took a European booking platform to a million users at Trainline, led Vrbo's platform migration at Expedia, and rebuilt Soldo's acquisition model to forecast lifetime value to around 95% accuracy. Costart Projects is where I build my own things, now with AI woven through the whole stack rather than bolted on.
A fleet of products, each shipped end to end.
Legal, education, home services, travel, voice — built and grown by one operator with a small trusted bench, and AI through the whole stack.
Also built & earlier
A Chrome extension that reads UK supermarket product pages and flags markers of ultra-processed food — E-numbers, emulsifiers, sweeteners — as you browse. Runs entirely in-browser and collects nothing.
A price-comparison and deal-alert service — co-founded and run for three years. The first startup chapter before Costart Projects.
I ship the thing, and I work out why it grows.
I've spent most of my career being the person who both ships the thing and works out why it's growing. The thread through all of it is a bias for the “how” over the “what”: get close to the work, model it honestly, and let the numbers decide. Today I run Costart Projects as a solo founder, building products with a small trusted bench of designers and developers — and doing it at a scale that used to need a team. This site is both halves of that: the products I'm building, and the operator behind them.
Built the European booking site from a proof of concept into a platform serving a million users.
Led the Vrbo/HomeAway platform migration, turning a projected loss into measurable gains.
Replaced a cost-per-acquisition model with a lifetime-value one, forecasting from 60 days of activity to ~95% accuracy.
Robert Costart
Founder, Costart Projects. Builds products; owns the growth model behind them.
Connect on LinkedIn →What used to need a team, run by one operator.
AI woven through the whole stack — research, build, content, growth — isn't a feature I bolt on. It's how a single founder now operates at team scale. That's the same edge I bring to growth teams that want to move faster with less.
Build end to end
Product, engineering and design in one head — from first commit to live, without hand-off friction.
Own the growth maths
Model acquisition and retention honestly, forecast lifetime value, and let the numbers pick the roadmap.
AI through the stack
Agents and automation compress research, content and ops from days into hours — across a whole fleet of products.
Building something, or scaling a growth team?
I take on a small number of build and advisory engagements. If AI at the core of your product and growth is where you're headed, let's talk.