Senior Rails Engineer -- Fintech Platform (Thoughtful Applications Only -- Cover Letter Required)

Compensation: Competitive, commensurate with experience About Topkey Topkey is a rapidly-growing fintech platform for short-term rental managers. We're particularly proud that 95%+ of all companies that onboard to Topkey never leave (I believe it is closer to 99%.) We offer deposit accounts, credit cards, full bill-pay, external cards, and expense management—all in one Rails monolith on the latest Ruby/Rails. With $1M+ ARR, zero churn (at the time of posting this), and a small, tight-knit engineering team, you’ll have a huge impact on our roadmap, our stack, and our customers’ success. We’re backed by top-tier investors like Felicis Ventures, Andreessen Horowitz (a16z), and Y Combinator. Topkey is recognized as one of the top emerging vertical startups, and our trajectory is steep. We’re looking for driven individuals to join our team and help shape the future of financial infrastructure in the $110 billion hospitality market. We’ve been featured in numerous media outlets, including Axios , Wall Street Journal , Fortune , Phocuswire , Short Term Rentalz , and Fintech Global . \*Topkey is a financial technology company and is not a bank. Banking services provided by Thread Bank; Member FDIC. Application Requirements: Applications without a personalized cover letter will not be considered Generic or AI-generated applications will be automatically rejected. We're looking for engineers who are passionate about Rails - when applying, mention your favorite gem and a brief reason why. We value authentic communication and want to hear YOUR voice What You'll Do Own features end-to-end in our Rails monolith (Rails 8+, Ruby 3.x) Build rich, reactive UIs with Hotwire/Turbo, Stimulus, and Tailwind CSS Integrate with external APIs (Plaid, Stripe, Unit, etc.) securely and robustly Use large context LLMs (Claude, Gemini, ChatGPT, etc.) to accelerate coding, QA, and spec writing Participate in architecture discussions -- help us evolve our beautiful monolith Work closely with product and founders to take specs from prototype to prod Ship daily/weekly, review critically, and treat AI as a multiplier—not a replacement for good judgment. (BTW, include the phrase 'beautiful monolith' in your application to show you've read this far) Optimize performance, reliability, and scalability of our core platform Act as your own pair programmer—debugging, prompting, reviewing AI-generated code for quality (the eng team will also review, but the initial onus is on the contributor) You Have 5+ years building production-grade Rails applications Deep expertise in Ruby, Rails conventions, background jobs, and service objects in a growing monolith Confidence reviewing, prompting, and editing AI-generated code from tools like Claude, Devin, Gemini, Cursor, etc. A reflexive approach to using AI in specs, code, QA, testing, and documentation Strong front-end chops: Stimulus/turbo/hotwire, components, etc. Experience designing and consuming REST APIs Solid SQL skills (PostgreSQL) and an eye for data modeling Track record writing maintainable test suites (RSpec) and CI pipelines Comfort working autonomously and asynchronously in a high-trust, high-output team Nice-to-Haves Previous fintech or payments or accounting experience Familiarity with Plaid, Stripe, or similar Experience with observability tooling (NewRelic, Honeybadger, etc.) Open-source contributions or personal projects you’re proud of Contributions to open-source or side projects involving AI/LLMs Required: Cover Letter Please submit a cover letter (max 500 words) that addresses: A specific technical challenge you've solved in a Rails application and your approach Your experience using AI tools in development and how you ensure code quality Why Topkey's mission in the short-term rental space (or real-estate in general) interests you specifically Include the word "monolith" somewhere in your cover letter to confirm you've read this posting Please share a brief story about a time when AI tools helped or hindered your development process Required: Technical Questions Describe a time when you had to optimize a slow Rails query. What was your approach? What's your experience with Hotwire/Turbo for building reactive UIs? Describe your approach to handling background jobs at scale in a Rails monolith How do you approach code review for AI-generated code? What feature would you like to see Rails core include out-of-the-box that isn't currently available, and why? Perks & Benefits Remote-friendly Generous PTO and paid holidays Equity in a high-growth startup Generous professional development stipend Home-office setup budget Health, dental, and vision insurance (U.S.) + 401(k) match Optional But Encouraged: Link to a recent PR or code sample that demonstrates your Rails expertise GitHub profile with Rails projects — \*Topkey is a financial technology company and is not a bank. Banking services provided by Thread Bank; Member FDIC.