Full Stack Engineer Ruby on Rails TypeScript Mentor Fintech & SaaS Volunteer Full Stack Engineer Ruby on Rails TypeScript Mentor Fintech & SaaS Volunteer
Portfolio · jack.hartzler.dev

Jack
Hartzler.

Hi, I'm Jack. At work, I build software that people depend on to do their jobs. Currently, that means loan officers processing auto refi's and lender integrations to get our customers the best possible rates. In the past, I worked on enterprise SaaS for some of the largest customer experience teams in the world. I love backend coding but I'm comfortable the whole way up and down the stack. Off work, I'm a longtime volunteer mentor for college students and teens — and that's why I'm building RoomRally, a party game platform for in-person connection between young people and the adults who support them.

Jack Hartzler
J
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Side Project

Web App

RoomRally

A real-time multiplayer party game platform for youth workers, teachers, and camp counselors. Players join via room codes on their phones while a shared screen drives the action. Built for safe, moderated use in mixed group settings.

Rails Turbo Streams WebSockets Redis Hotwire Stimulus
View Project →
Under Active Development — More Coming Soon
Features
Live

Comedy Clash

A Quiplash-style prompt game where players submit the funniest answers and vote on the best.

Live

Think Fast!

A Kahoot-style speed trivia game with time-based scoring and real-time leaderboards.

Live

AI Game Content Generation

Create a fully themed game in one click. LLM integration generates custom prompts, questions, and content so hosts can spin up a unique experience in seconds.

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Experience

Work History

Full Stack Software Engineer

2022 – Present
Caribou Financial
  • Designed a product discount feature in Rails generating $7k+ revenue weekly while simplifying the DB schema
  • Built Auth0 integrations for customers and business partners to securely access internal systems
  • Created API caches in TypeScript/Node to store vendor requests and responses, preventing outages when 3rd-party services go down
  • Patched security vulns across multiple services to unblock SOC2 compliance; wrote the playbook for other engineers to follow
  • Only non-staff engineer selected for a pilot tier-2 support rotation

Software Engineer II

2020 – 2022
Medallia
  • Built REST and GraphQL APIs in Java for Medallia's core enterprise SaaS product
  • Became the go-to engineer for critical business logic areas while simplifying the domain
  • Part of on-call rotation to fix customer issues and ship hotfixes

Earlier Experience

Software Engineer

2019 – 2020
Potomac IT Group
  • Contributed to a new web app on Angular / Tomcat / Java
  • Mentored new engineers through code reviews and pair programming

Software Engineer

2017 – 2019
CA Technologies
  • Led a CLI plugin from proof-of-concept to production release in Node.js
  • Built features for an on-prem B2B resource monitoring web app in Angular

Software Engineer

2016 – 2017
Madcap Software
  • Developed new features for a technical writing tool including a responsive content resizer

B.S. Computer Science

2016
UC San Diego
Download Resume PDF
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Technologies

Ruby on Rails
Hotwire
TypeScript
HTML / CSS
PostgreSQL
REST API Design
GraphQL
Node.js
Java
Spring
Docker
Kafka
Terraform
DataDog
Elastic
Unix / Bash
Claude Code
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About Me

The Long Version

Nice to meet you! I'm a dude from SoCal who learned to code a little bit at UCSD. Since then, I've worked as a developer my whole career, and learned to code a lot bit more. Right now I work at Caribou Financial. We fix bad car loans!

Throughout my career, I've also always volunteered as a mentor for younger people - college students, teens, and kids. I believe that every young person needs loving, stable, adult mentors in their lives. I was fortunate to have many growing up, and now I get to pay it forward to others.

That mission has taken me to several states - Pittsburgh, Pennsylvania, where I met my wife, then the DC area, then to Ohio to help start a group at 'the' Ohio State University, and most recently back to the DC area. Come hang out with me at the monuments or in downtown Vienna!

At home, I'm a barista to my amazing wife and jungle gym to two beautiful daughters. I also have a small coffee problem and enjoy roasting, grinding, and brewing all the anaerobically processed Ethiopian and South American coffee I can get my hands on.

Every word of this bio was written by me. The code is another story... AI is very convenient for that :)

Fun Facts

I once made 15 gallons of cold brew at once in order to sell it for a fundraiser. We didn't quite sell out. But it was close.

🖋️

My major was Computer Science, but my favorite college class was playwriting. Since then, I've written or contributed as an editor to several skits and one-act plays that have been performed live for groups of 50-100+ people.

🏕

I've spent 10+ years volunteering with teenagers on a weekly basis. Worth it!

📖

My favorite Youtube Channel is the Bible Project. Whether you're Christian or not, they're super engaging and relevant videos about the meaning and history of scripture.

🎸

I didn't build software in high school, but I did build a working full-scale electric bass in woodshop.