Senior Java Code Reviewer

About OpenTrain

OpenTrain is the #1 platform for finding and building careers in AI training and data labeling. We connect skilled contributors with projects that shape how AI models learn, grow professional experience, and get paid for high-impact work.

We focus on real, remote-first opportunities that let you work flexibly while contributing to next-generation AI systems. This role is hired and managed directly by OpenTrain AI.

About AI training work

AI training (data labeling/annotation) is the human side of building intelligent systems: people create, check, and rate examples that models learn from. This project focuses on code-review tasks where human judgment ensures model outputs are correct, secure, and production-ready.

These roles are ideal if you want part-time, remote work that leverages technical expertise to directly influence how AI behaves.

The Role

You will audit annotator evaluations of AI-generated Java code. Your work ensures that every review accurately reflects functional correctness, security, and performance against the prompt and our rubric.

This is a contractor, part-time role requiring 20+ hours/week. Work is fully remote and worldwide; compensation is $25 USD per hour.

What you'll do

Operate within a structured QA workflow to validate and correct code reviews performed by annotators. Provide concise, actionable feedback and ensure consistency with the quality rubric.

• Compile and run submitted Java snippets in an isolated sandbox or container to verify functionality and prompt compliance.
• Check for secure-coding issues (OWASP concerns, deserialization risks, injection, race conditions) and flag or fix mis-ratings.
• Evaluate performance characteristics and JVM-related concerns (GC behavior, JIT, profiling signals) against expectations.
• Assess unit and integration tests (JUnit 5, Testcontainers, TestNG), coverage, and test reliability, and advise on gaps.
• Review concurrency, thread-safety, locks, CompletableFutures, and reactive streams implementations for correctness.
• Correct annotator score errors, add targeted feedback, and document decisions to maintain rubric alignment.
• Use ticketing and annotation tools to track issues, raise clarifying questions, and mentor annotators on best practices.

Requirements

You must be able to produce concise written feedback in clear English and follow rubric-driven QA. Preserve all technical requirements listed below when applying.

• 7+ years professional Java development, QA, or dedicated code-review experience.
• Deep expertise in modern Java (11–21), core APIs, and JVM internals including GC and JIT behavior.
• Advanced testing and debugging skills with JUnit 5, TestNG, Mockito, Testcontainers, and coverage tools like JaCoCo.
• Proven ability to analyze and debug concurrency and multithreading issues (locks, thread-safety, CompletableFuture, reactive streams).
• Strong secure-coding knowledge: OWASP Top 10, deserialization attacks, injection, race conditions, and permission flaws.
• Comfortable compiling and executing code in sandboxed or containerized environments to validate behavior.
• Familiarity with Maven/Gradle, Dockerized builds, CI/CD pipelines (GitHub Actions, GitLab CI), and code-review platforms.
• Experience with rubric-based scoring, checklist-driven reviews, and ticketing systems (Jira, Asana).
• Excellent written English (B2+ CEFR) for concise feedback and mentoring.

Nice to have

These are optional but helpful and may influence selection when candidates are otherwise similar.

• Experience evaluating outputs from LLMs, RLHF pipelines, or prior AI/ML data-labeling projects.
• Familiarity with coverage and profiling tooling beyond JaCoCo, such as async-profiler or VisualVM.
• Prior mentoring or QA leadership in distributed annotation teams.

How it works & how to apply

This is a remote contractor position. Expect a structured onboarding to our QA rubric, sandbox environment, and ticketing tools. You'll work 20+ hours/week and log hours for hourly pay at $25 USD/hour.

Application review will focus on demonstrated Java experience, examples of code review or QA work, and written English clarity. Selected applicants will complete a short practical validation that includes reviewing and running small Java snippets in a sandbox.

• Employment type: Contractor, Part-time; worldwide applicants welcome.
• Time commitment: 20+ hours per week.
• Pay: $25 USD per hour (hourly contractor pay).
• Application steps: submit resume, show examples or links to prior code-review/QA work, and complete a short proof-of-work validation.