Mobile apps that ship
Expo and React Native for iOS and Android: EAS builds, over-the-air updates that can’t brick the app, and App Store and Play releases.
ExpoReact NativeEASMaestro
Contract and consulting · Seattle, working globally
Subscription apps that ship, with numbers you can trust.
I’m Jon Zaro, a full-stack and mobile engineer and lead developer on Burn by Cara Loren. I take production systems that are quietly wrong, like payments, analytics and releases, and make them measurable, reversible and safe to ship.
Shipped at Burn
Burn by Cara Loren · iOS, Android, web
What changed at Burn
- Releases12 hrs → 5 minTime to recover from a bad releaseA broken update once took 12 hours to fix. Now it rolls back in minutes.Read the case study
- Analytics80% → 47%The team’s key growth number, correctedChecked against billing data, the real conversion rate was far lower than the one being used.Read the case study
- Billing data90% fewerSubscriptions stuck in a failed-payment stateRepaired live billing records in place, with an undo for every change.Read the case study
- Integrations700+Stuck signup and payment tasks clearedReplaced a frozen Zapier queue with tested webhooks in our own API.Read the case study
From the people I’ve worked with
“He picks up complex systems and tools incredibly quickly — and doesn’t just learn them, he masters them and starts making an impact right away. … Our team runs more efficiently and has more time to focus on revenue growth because of his contributions.”
Victoria Lynn C. “He consistently took projects from concept to deployment, seamlessly handling both frontend and backend tasks. His expertise in AI tooling, particularly integrating custom GPT models into apps, made a huge impact on project efficiency and functionality.”
Steve R. “Jon is a strong engineer with a unique ability to think outside the box. While working with Jon, he was crucial in business automations utilizing various tools including AI. These automations led to saved time and efficiency as a company.”
Kevin M.
What I can take off your plate
The parts of an app that touch money.
Payments & subscriptions
Stripe and RevenueCat wired up so web and app purchases agree: signed webhooks, reconciliation, checkout and cancellation flows.
StripeRevenueCatWebhooksPostgres
Analytics you can steer by
Event tracking that fires once per real thing, identity that doesn’t merge strangers, and funnels checked against billing data.
PostHogFeature flagsA/B testsSQL
Release safety
CI gates, one-click rollback, migrations with tested down scripts, and deploy checks that prove what is actually running.
GitHub ActionsFly.ioVercelSentry
AI in your engineering workflow
AI code review in CI, agent workflows and Claude Code set up for your team, with tests and human review built in so speed doesn’t cost correctness.
Claude CodeGitHub ActionsAgent workflows
Integrations & automation
Zapier and Airtable glue moved into tested first-party webhooks, plus the email, CRM and billing integrations that keep your data in one place.
WebhooksKlaviyoZapierAirtable
How it works
Three steps, no surprises.
- 1
A free first call
Tell me what’s broken or what needs to ship. You’ll get a straight answer on whether I can help.
- 2
A written scope
What’s wrong, what I’d fix first, and how we’ll know it worked, agreed before any work starts.
- 3
Shipped and verified
Fixes land with tests and are checked in production, not just merged.
Case studies
Five problems from inside one production app.
Burn is a subscription fitness app on iOS, Android and the web. These are the problems I was trusted with there, from data repair to release safety, and what changed because of them.
Aug – Sep 2026
Repairing live subscription data, with an undo button
A backfill left subscription data double-counting paying users. I contained it, repaired it in production, and made every repair reversible.
14.9% → 6.1%Overstated active subscriptions after the first repair pass
TypeScript · Prisma · PostgreSQLRead case study
May – Jul 2026
Replacing a frozen Zapier pipeline with first-party webhooks
Signup and payment data ran through Zapier, and the queue had been frozen for two months. I moved it into the API with signed webhooks and tests.
700+Stuck Zapier tasks replaced by direct webhooks
Express · Prisma · PostgreSQLRead case study
May – Aug 2026
A launch crash, a postmortem, and a CI gate so it can't happen twice
An over-the-air update crashed the app on launch. I hotfixed it, wrote the postmortem, and built the gate and rollback tooling that stop a repeat.
< 5 minProduction rollback, down from a manual rebuild
Expo EAS Update · React Native · GitHub ActionsRead case study
May – Aug 2026
The activation metric was wrong. I rebuilt analytics on ground truth.
The team was steering by an activation threshold and trial counts that were both overstated. I re-checked them against billing data and rebuilt the metrics.
−33 ptsCorrection to the headline activation metric
PostHog · RevenueCat API · SQLRead case study
Sep – Oct 2026
Moving a live checkout site off WordPress, verified with real purchases
I ran the cutover of the signup and checkout site from WordPress to Vercel, and proved purchase, app access and cancellation worked with real money.
17 / 17Production paths verified on cutover day
Astro · Vercel · Stripe CheckoutRead case study
Your problem could be next.A short call, a straight answer on whether I can help.Book a call How I work
Four rules I don’t break.
- 01
Measure before I build
Most expensive bugs I’ve fixed were wrong numbers, not crashes. I reconcile against a second source before I trust a metric.
- 02
Every repair is reversible
Production data changes record their own undo. Releases have a rollback that takes minutes, not a rebuild.
- 03
Merged isn’t shipped
A fix counts when the deployed revision includes it and the data shows the problem stopped, not when the PR merges.
- 04
AI-accelerated, human-verified
I build with frontier models every day, and every change still ships with tests that fail without the fix.
Who you’d work with
Me, directly.
No account managers or hand-offs. I’ve led engineering on Burn since 2024, across the mobile app, the API, payments, analytics and releases. I’m based in Seattle and work with teams anywhere.
Have an app where the numbers don’t add up?
Tell me what’s breaking: payments, analytics, releases, or a mobile app that needs to ship. The first call is free, and you’ll leave with a clear next step.