Kotlin Developer

Senior Compiler Developer (Kotlin Compiler - Core)

JetBrains

ABOUT JETBRAINS We create intelligent software development tools for developers and teams. More than 15 million users, over 300,000 organizations, and 88 of the Fortune Global Top 100 companies rely on our products to solve real, complex problems. Our mission is simple: make development teams more productive and AI adoptable at scale. WHAT YOU’LL DO As part of the Kotlin Compiler team, you’ll take ownership of the central pipeline that connects the compiler’s frontend with multiple backends. This is deep, technical work that directly influences how Kotlin code is transformed, validated, and optimized. You’ll make architectural decisions that improve compiler performance and memory usage without sacrificing backward compatibility. Working closely with other Kotlin teams, your efforts will shape the evolution of the language and improve the daily experience for Kotlin developers worldwide. DAY TO DAY, YOU WILL: * Develop and implement new language features. * Implement and fine-tune intermediate representation (IR) lowering passes. * Investigate and resolve complex compiler bugs and edge cases. * Improve compiler performance and memory usage. * Work with other Kotlin teams to shape how the language evolves.  * Help improve the developer experience for Kotlin users. * Maintain and improve Kotlin infrastructure (IR/AST transformations, Klibs, and its backward compatibility). WHAT YOU’LL BRING * Precision. You care about every detail – from clean architecture to edge cases. * A strong sense of ownership. You’re comfortable taking on complex technical challenges. * Clear communication. You can explain your thinking and justify your technical decisions to other experts. * A collaborative mindset. You work well with teammates to find the best solutions. * A long-term focus on quality. You prioritize maintainability and backward compatibility over quick fixes. WHAT YOU’LL NEED * Proficiency in developing with Kotlin/JVM or Java. * A deep understanding of algorithms and data structures. * The proven ability to write clean, maintainable, and well-tested code. * Experience in compiler development would be a definite plus. * Experience developing Gradle plugins would be advantageous.  * Demonstrated success in optimizing JVM application performance would also be a plus. WHAT SUCCESS LOOKS LIKE In your first few months, you’ll dive into the compiler's central pipeline and start taking ownership of specific lowering passes and bug fixes. Over time, you’ll be making significant architectural contributions that measurably improve compiler performance and memory usage. Success means earning the trust of your team through clear communication, well-reasoned decisions, and code that leaves the Kotlin compiler cleaner and more robust than you found it. Why join JetBrains?  * Strong base salary. We offer competitive pay that reflects your skills and experience. * Flexible work location. Enjoy the freedom to work from home or from the office. * Remote work. Spend up to 30 days per year working remotely from abroad. * Extra time off. More days to relax, recharge, and do the things you love. * Medical insurance allowance. Enjoy peace of mind for you and your family * Learning and development opportunities. Access to conferences, courses, and language classes. * Relocation support. We help make your move as smooth and stress-free as possible.  * Language classes. Pick up the local language or sharpen your English skills. * Fuel your day. Enjoy a hot meal or receive a lunch allowance on workdays. * Mental health support. To help you feel your best, we provide easy access to professional mental health services. * Sports benefit. Enjoy an on-site gym or sports club stipend. * Internal events. Join company-wide celebrations and team gatherings. *Some benefits may vary depending on location. #LI-IM1 We are an equal opportunity employer We know great ideas can come from anyone, anywhere. That’s why we do our best to create an open and inclusive workplace – one that welcomes everyone regardless of their background, identity, religion, age, accessibility needs, or orientation. We process the data provided in your job application in accordance with the Recruitment Privacy Policy.

Senior Java/Kotlin Developer

Malt

🪐 Discover our galaxy   Join the Future of Work ! Malt is Europe's leading freelance marketplace, connecting over 1,000,000 talented freelancers with 100,000+ companies. Founded in 2013, we're transforming how work gets done through our tech-powered, human-centered platform. What makes us different:   - A diverse team of 600 Malters across 6 European countries - A culture that champions equality (50% of our Comex are women) and inclusive growth - Backed by top investors including ISAI, Serena Capital, Eurazeo Growth, Goldman Sachs, and BPI - A mission to give everyone the freedom to work differently   Ready to help shape the future of work? Your next chapter starts here! 🪐

Senior Research Engineer (Agentic Behavior)

JetBrains

At JetBrains, code is our passion. Ever since we started, back in 2000, we've been striving to make the strongest, most effective developer tools on earth. Today, AI-powered coding agents are becoming a core part of how developers write Kotlin – and we want to make sure they write it well. The Kotlin AI Value Stream team is responsible for how AI agents understand, generate, and improve Kotlin code across all platforms: Android, Kotlin Multiplatform, server-side, web, desktop, and others. We build the evaluation infrastructure, error analysis tools, and post-training pipelines that measure and improve agent behavior on real Kotlin developer tasks. As a Research Engineer on this team, you'll own the end-to-end loop: Analyze how agents fail on Kotlin → build evals that capture those failures → research and implement methods to fix them → measure the improvement. Your work will directly shape how millions of developers experience Kotlin through AI coding agents. AS PART OF OUR TEAM, YOU WILL: Build tools for agentic error analysis * Design and implement tooling to systematically capture, classify, and analyse errors that AI coding agents make when generating Kotlin code. * Build observability pipelines over agentic traces – mining patterns from agent sessions in JetBrains IDEs, Junie, Claude Code, Cursor, and other coding agents. Build evaluation pipelines * Design, implement, and maintain evaluation pipelines that measure Kotlin code generation quality across dimensions, including correctness, idiomaticity, build success, framework usage, and test coverage. * Build simulation environments where coding agents can be measured on realistic Kotlin developer tasks – from greenfield KMP projects and Gradle dependency management to migrating Spring applications from Java to Kotlin. * Own evaluation infrastructure: metrics, experiment tracking, automated regression checks, and reproducible benchmarking. Research methods for improving agent and model behavior on Kotlin * Experiment with post-training techniques (SFT, DPO, GRPO) to improve how models handle Kotlin-specific patterns, idioms, and frameworks. * Investigate context engineering approaches: CLAUDE.md/AGENTS.md files, compiler-as-verifier feedback loops, Kotlin LSP integration, and MCP-based tooling. * Run experiments to measure impact: A/B comparisons, benchmark suites, and before/after analyses on real codebases. * Collaborate with model providers (Anthropic, OpenAI, and Google) to translate Kotlin-specific findings into model improvements. Build public Kotlin benchmarks * Design and build open-source benchmarks that measure AI coding agent performance on Kotlin tasks and eventually become the standard reference for the ecosystem. * Create task datasets covering the breadth of Kotlin usage: the server side (Spring, Ktor), multiplatform projects (KMP), build systems (Gradle), Android, library development, and others. * Include both mined real-world tasks and carefully designed synthetic tasks that test specific Kotlin capabilities. * Maintain and evolve benchmarks as models improve, ensuring they remain challenging, relevant, and contamination-resistant. WE'LL BE HAPPY TO HAVE YOU ON BOARD IF YOU HAVE: * Hands-on experience building evaluation or analysis pipelines for LLMs or AI coding agents in a research or production setting. * Strong Python engineering skills (at least three years), with the ability to write clean, maintainable code in data-heavy and ML-adjacent codebases. * Experience with data analysis at scale: querying large datasets (SQL/Athena), building data pipelines, and performing statistical analysis of experimental results. * The ability to own projects end to end – from identifying a problem in agent traces to designing an eval, running experiments, and shipping a fix. * A product-aware mindset: You care about how agents are actually used by developers and can translate real failure modes into evaluation and training work. * Familiarity with Kotlin or a strong willingness to develop deep Kotlin expertise (you'll be living in Kotlin codebases daily). OUR IDEAL CANDIDATE WOULD ALSO HAVE EXPERIENCE WITH: * Post-training LLMs: SFT, RLHF, DPO, GRPO – either hands-on training or designing the data and reward pipelines that feed into training. * Modern deep learning frameworks (PyTorch) and LLM training stacks (TRL, verl, Megatron, or similar). * AI agent development: tool-using agents, multi-step coding workflows, agentic frameworks. * Evaluation frameworks and tools: Inspect AI, Promptfoo, LM-evaluation-harness, or custom eval pipelines. * Experiment tracking and observability: Weights & Biases, MLflow, Langfuse, or similar. * The Kotlin ecosystem: Android, Gradle, KMP, Spring, Ktor – with an understanding of the developer workflows that agents need to support. * Contributing to or maintaining open-source projects, especially benchmarks or evaluation tools. Don't check every box? That's okay – if you're excited about this work and bring strong fundamentals, we'd love to hear from you. We're happy to talk and provide the training you need to grow into the role. WHY JOIN JETBRAINS?  * Strong base salary. We offer competitive pay that reflects your skills and experience. * Flexible work location. Enjoy the freedom to work from home or from the office. * Remote work. Spend up to 30 days per year working remotely from abroad. * Extra time off. More days to relax, recharge, and do the things you love. * Medical insurance allowance. Enjoy peace of mind for you and your family * Learning and development opportunities. Access to conferences, courses, and language classes. * Relocation support. We help make your move as smooth and stress-free as possible.  * Language classes. Pick up the local language or sharpen your English skills. * Fuel your day. Enjoy a hot meal or receive a lunch allowance on workdays. * Mental health support. To help you feel your best, we provide easy access to professional mental health services. * Sports benefit. Enjoy an on-site gym or sports club stipend. * Internal events. Join company-wide celebrations and team gatherings. *Some benefits may vary depending on location. #LI-KP1 We are an equal opportunity employer We know great ideas can come from anyone, anywhere. That’s why we do our best to create an open and inclusive workplace – one that welcomes everyone regardless of their background, identity, religion, age, accessibility needs, or orientation. We process the data provided in your job application in accordance with the Recruitment Privacy Policy.