Job Description

Own your work, skip meetings, and ship code used by millions.

At Koinly, we’re hiring a Senior Ruby Developer to build and maintain scalable backend systems for over 2 million crypto investors. You’ll write high-performance Ruby/Rails code and continuously improve speed, reliability, and the overall user experience.

We’re looking for someone who excels at performance and data at scale, is comfortable with queries, indexes, and large imports, and is motivated to make systems faster and more efficient.

We’re a profitable, bootstrapped, remote-first startup founded in 2018 with a strong product–market fit in the fast-growing crypto tax space. If you value autonomy, high engineering standards, and clear communication over heavy process and meetings, you’ll fit right in at Koinly.

Key details at a glance

• Location: Remote - (Minimum 4-hour overlap with UK time (9 am–6 pm) required)

• 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 reached product–market fit in a high-scale financial domain and now need to keep improving performance and reliability while shipping new features. This means tackling challenges in:

• Data architecture: Handling billions of rows, large CSVs, and high-throughput APIs

• Performance: Query tuning, caching, and background jobs

• System design: Scaling Ruby services that process terabytes of data reliably

What you’ll do:

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

• Handle massive datasets (billions of transactions) efficiently and reliably.

• Debug production issues across code, data, and infrastructure.

• Write clean, tested, maintainable Ruby at scale.

• Prioritize performance, clarity, and simplicity in code and systems.

• Participate occasionally in on-call rotation (rare issues due to strong testing).

• Keep up with Ruby best practices and emerging tools.

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: Bootstrapped, profitable, hyper-growth startup.
💎 Pure Ruby backend: Focused, high-performance code.
🧠Autonomy-first: Deep work, minimal meetings
📊 Real scale: Billions of trades, 1000+ integrations, millions of users
💥 Small team, big impact: Millions of users, ~35 people company-wide.
🪶 No corporate theatre: Zero bureaucracy, high trust, high ownership.
🕰 Flexible by default: Fully remote, results-driven, async communication.
🧩 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.