Senior Ruby Engineer | Remote (Europe) & Async-first

Own your work, skip the meetings, and write code that directly impacts millions of users.

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 need an engineer who thinks in data pipelines, indexes, and execution plans , not just models and controllers. Someone who gets irrationally motivated by shaving milliseconds off a query, or turning an hour-long CSV import into minutes.

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 details at a glance

• Location: Remote - preference for Europe-based candidates

• Salary: USD $80–$90K per year

• Type : Full-time (contractor - B2B)

• Perks:

  • 32 days of PTO

  • Async culture

  • Remote-first

  • Flexible working schedule

  • High level of autonomy

• Experience level : 6+ years of professional Ruby experience.

• Start date : ASAP

• Team size : 10 person engineering team

• Main responsibilities : Design, optimize, and scale Ruby backend services handling billions of records, ensuring performance, reliability, and clean code at massive scale.

Why this role exists

We’ve hit product–market fit in a high-scale, complex financial domain. Now we need to keep pushing performance and reliability while shipping new features. That means solving hard problems in:

• Data architecture: Making billions of rows and massive CSVs play nicely with high-throughput APIs.

• Performance optimization: Query tuning, caching strategies, background job orchestration.

• System design: Scaling Ruby microservices that process terabytes of data without falling over.

What you’ll do:

• Own backend services end-to-end: design, build, refactor, and optimize.

• Work with huge datasets (billions of transactions) and make them fast, reliable, and cost-efficient.

• Debug gnarly production issues that live at the intersection of code, data, and infrastructure.

• Write clean, tested, maintainable Ruby that holds up under scale.

• Champion performance, clarity, and simplicity in code and system design.

• Occasionally take part in on-call rotation (we have very few prod issues, high coverage, and careful releases are the norm here).

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

What you bring:

• 6+ years of professional Ruby experience.

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

• Strong problem-solving and debugging skills.

• Experience designing and scaling backend systems (microservices, APIs, background jobs).

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

• A track record of taking full ownership of complex features or systems.

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

Bonus points if you’ve:

• Experience with high-volume CSV/data ingestion pipelines.

• Familiarity with performance profiling tools in Ruby.

• Background in DeFi, blockchain, or fintech.

• Side projects that show your love for technical puzzles.

Probably not a right fit if:

• Ruby/Rails isn’t your main language or only occasional experience.

• Limited backend ownership, system design, or microservices experience.

• Rails work mostly UI/features with light SQL, no pipeline/data/query optimization.

• Exclusive infra/SRE or app-only focus, lacking hybrid backend/data skills.

• Prefer structured processes, frequent meetings, or struggle with async work.

• Dislike ambiguity, messy, or inconsistent data.

• Juggling multiple part-time roles; can’t commit full-time.

Koinly's engineering culture

⚙️ Craftsmanship matters: we value deep thinking, well-structured systems, and clean code.

💬 Async-first collaboration: clarity and autonomy come through written communication.

🚀 Impact through ownership: engineers drive projects end to end.

🌍 Remote: we trust people to work flexibly and deliver excellence from anywhere.

Why join Koinly

🏗 Built for builders: A profitable, bootstrapped startup in a hyper-growth industry.
💎 Pure Ruby backend: No language sprawl or over-engineering.
🧠 Autonomy-first: Async communication, deep work, minimal meetings.
📊 Massive scale: Billions of trades and 1000+ integrations.
💥 Small team, big impact: Millions of users, ~34 people company-wide.
🪶 No corporate theatre: Zero bureaucracy, high trust, high ownership.
🕰 Flexible by default: Fully remote, async, and results-oriented.
🧩 Crypto-adjacent without the hype: We’re a painkiller, not a multivitamin. We solve real issues.

Join Koinly and design systems of crypto tax at massive scale. Apply today!

Due to the nature of our business and external requirements, we perform background checks on all potential team members, passing which is a prerequisite to join Koinly.