Senior Ruby Engineer | Remote-first (Europe only) |...

At Koinly, we’re looking for a Senior Ruby Developer to help design, build, and maintain scalable backend systems that power crypto tax reporting for over 1.5 million crypto investors. You’ll write clean, efficient, and high-performance code – not to just ship new features, but to continuously optimize speed, reliability, and user experience across our Ruby (and Ruby on Rails)-powered architecture.

We’re a fully remote-first, async-first startup with product-market fit in a niche (and booming) domain: crypto taxes. Our lean team of 35 people (10 in engineering) is mostly spread across EMEA. We value autonomy, technical excellence, and clear communication over meetings and process complexity.

Key role details

• Department: Tech
• Location: Must be based in Europe
• Salary: USD $80,000-$90,000 per year
• Type: Full-time, remote (Contractor - B2B)
• Timezone: Ideally UK ±2 hours
• Team size: 10 engineers in a 35-person team

About us

🌕 We’re on a mission to make crypto taxes simple.

Since 2019, we’ve grown to 1.5M+ users by tackling one of crypto’s messiest challenges: tax reporting. Our platform helps investors stay compliant, track their assets across hundreds of wallets, exchanges, and DeFi platforms, and save hours of time. Just see what our customers have to say about us.

Behind that focus towards simplicity lies a deeply technical product, built on large-scale data processing and integrations with hundreds of platforms. Our stack is Ruby-heavy, our test coverage is high, and our expectations on code quality and system performance are even higher.

If you’re someone who thrives on autonomy, enjoys a tight feedback loop with product, values radical candor within the team, loves building clean, efficient systems without unnecessary meetings — Koinly is what you’re looking for.

Why Koinly is different

• A team that punches far above its size: 10 engineers powering a product used by 1.5M+ people.

• No fluff, no chaos. Just clean systems, deep focus, and real outcomes.

• We operate on radical candor, async documentation, and trust.

• Engineering is central to the product — not a service layer.

The role

As a Sr. Ruby Developer, you’ll be responsible for writing clean, modern code that adheres to best practices. We’re looking for a self-motivated individual who takes pride in their work, values high-quality code, and cares deeply about the overall application experience.

We pride ourselves on having very high test coverage and rarely having any prod issues. Our backend follows a microservices architecture, consisting of multiple small services that collectively power the user experience.

If you have a data mindset, a sharp eye for clean, scalable code, a bias for ownership, and want to work in the fast-growing crypto space, apply now!

What you’ll do:

• Design, build, and maintain scalable and efficient Ruby applications.

• Own and implement new product features end-to-end.

• Maintain existing code while ensuring high performance and responsiveness.

• Write clean, maintainable, and efficient code following best practices.

• Optimize applications for performance, speed and scalability.

• Implement automated tests and ensure robust code quality.

• Debug and troubleshoot complex issues across production and development environments.

• Work closely with product managers, designers, and other engineers in a focused async loop.

• Stay up-to-date with emerging technologies and best practices in Ruby development.

• May have on-call responsibilities.

What you’ll bring:

• 5+ years of professional Ruby experience.

• Strong SQL skills, including performance tuning and complex queries.

• Strong problem-solving and debugging skills — you leave code better than you found it.

• Experience working with RESTful APIs, microservices, and third-party integrations.

• Familiarity with background job processing tools (Sidekiq, etc.).

• Proficiency in at least 2 programming languages.

• Eagerness to work with a high-standard engineering team, CI/CD, and testing.

• Clear, concise written and verbal communication in English.

• You favor asynchronous work over meetings.

• You're based in Europe and have experience working remotely in async environments.

• Comfort with feedback loops and a high-ownership mindset.

Bonus points for:

• React experience.

• Interest in DeFi, blockchain, or emerging languages like Rust is a major advantage.

• A CS degree (or deep hands-on background via data science or backend track).

What you’ll get:

• A lean, no-BS engineering environment with high-trust and high-impact engineering environment with zero fluff that ships with quality.

• Flat operations with full ownership and autonomy.

• An async-first work environment that favors clear communication and documentation over meetings.

• Focused, deep work — we respect your time, energy, and limits.

• A role where every line of code you write has a direct user impact.

• A culture that values feedback, autonomy, and outcome-driven work

• USD 80–90K per year (B2B contract).

• 32 paid days off per annum (incl. public holidays).

• Remote and async-first work environment.

• Co-working space budget, if desired.

Your first month

This is the most decisive part of your tenure at Koinly. We’ll assess how quickly you can get operational and contribute value. A good benchmark? Try Koinly yourself. If the product doesn’t click for you quickly, building it won’t be easier. We hold our work to the same standard we expect for users: getting results fast, with clarity and confidence. After all, we expect our users to be able to do their taxes with Koinly in under 20 minutes, and we build accordingly.

Our interview process

1. An initial call with the talent team (30 mins).

2. A take-home task (~3 hours).

3. Technical interview with live-coding and architecture problems (90 mins).

4. Final call with the hiring manager (30 mins).

Our values & work environment

As a startup we value efficiency above all else. We hire people who write clear code, ask sharp questions, and bring initiative and craftmanship to their work — without needing to be told twice.

We work in a flat, focused team where every person plays a critical role in delivering value to our users. There are no middle managers here, and no pointless meetings. We optimize for deep work, clear communication and documentation, and measurable impact.

We thrive on radical candor, ownership and curiosity. If you’re someone who can prioritize independently, choose the right tools, and build efficient systems that multiply your time - you’ll fit right in.

If you love clean systems, fast execution, and collaborating with smart, driven teammates – we’d love to hear from you.

How to apply

Ready to join a lean, async-first team building real-world tools for the crypto space?

Click “Apply for this job” to submit your CV