Senior Ruby Engineer | Remote-first (EMEA) | Crypto Tax

Koinly; London; Remote; USD 80,000 - 90,000; Full time

Job summary

A remote-first startup, Koinly is seeking a Senior Ruby Developer to design and maintain scalable backend systems for crypto tax reporting. Ideal candidates will have 5+ years of Ruby experience, strong SQL skills, and a passion for writing clean, maintainable code in a fast-paced environment.

Benefits

32 paid days off per annum

Remote and async-first work environment

Co-working space budget

Qualifications

• 5+ years of professional Ruby experience.
• A CS degree or deep hands-on background in backend development.
• Strong SQL skills, including performance tuning.

Responsibilities

• Design, build, and maintain scalable Ruby microservices.
• Debug and troubleshoot complex issues.
• Refactor large code bases to improve performance.

Skills

Ruby

SQL

Problem Solving

Debugging

Microservices

RESTful APIs

Communication

Education

Computer Science degree

Tools

Sidekiq

Job description

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. If you value autonomy, technical excellence, and clear communication over meetings and process complexity, Koinly is the place for you.

Key role details

• Department: Tech
• Location: EMEA, preferably 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 900+ integrations. Our stack is Ruby-heavy, our test coverage is high, and our expectations on code quality and system performance are even higher.

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 Ruby microservices used across the Koinly platform.

• Work with massive datasets — billions of transactions and millions of users — with a focus on database optimization and performance.

• Refactor large code bases to remove complexity.

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

• 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.

• Implement automated tests and ensure robust code quality.

• Once in a while you’ll have on-call responsibilities.

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

What you’ll bring:

• 5+ years of professional Ruby experience.

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

• 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'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.

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

Your first few weeks at Koinly are all about mutual discovery. You’ll receive hands-on tasks that help us understand your technical strengths and how you operate in our async-first, ownership-driven environment. At the same time, you’ll get to explore whether our way of working challenges and supports you in the right ways.

We’re big on clarity, autonomy, and getting things done — and we hold our own product to the same standards. We expect our users to get their taxes done in under 20 minutes — and we aim to build with that same focus and confidence. A good benchmark? Try Koinly yourself. If the product doesn’t click for you quickly, building it won’t be easier.

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 founder (30 mins).

How to apply

Ready to join a lean, async-first team building real-world tools for the crypto space?We’re looking for clarity, ownership, and technical sharpness.

Click “Apply for this job” to submit your CV.