Legacy Codebase Migration Expert | $200/hr Remote
Overview
Mercor pairs senior engineers with a frontier AI research lab to modernize aging codebases at scale. The work spans planning and executing complex migrations across production systems in finance, healthcare, and telecom, then evaluating AI-generated migration solutions for correctness and production readiness. Engineers preserve behavior, data integrity, and security through language, framework, database, and infrastructure shifts. The engagement is part-time, remote, and pays $200 per hour.
What You'll Do5
- 1Plan and execute complex codebase migrations while reviewing migration output for correctness and completeness.
- 2Map legacy code, dependencies, APIs, databases, build systems, and infrastructure to determine safe migration paths.
- 3Maintain functionality, backward compatibility, data integrity, security, and performance throughout each migration.
- 4Create test suites and validation strategies that catch regressions and behavioral differences.
- 5Assess AI-generated migration solutions for production readiness, maintainability, and alignment with requirements.
Requirements7
- 15+ years in professional software engineering, with a Senior, Staff, Principal, or equivalent title.
- 2Ownership of, or major contributions to, large-scale production migrations in mature codebases.
- 3Hands-on expertise in at least one migration domain: language version upgrades (Java 8 to 17/21, .NET, Python 2 to 3, PHP 7 to 8), language rewrites (COBOL to Java/Python, JavaScript to TypeScript), framework upgrades (Angular, Rails, Django, Spring, ASP.NET, Next.js, Astro), database/ORM shifts (Oracle to PostgreSQL, SQL to NoSQL, Hibernate to jOOQ, Sequelize to Prisma), infrastructure containerization (VM to Docker/Kubernetes), CI/CD modernization (Jenkins to GitHub Actions, GitLab CI), build tooling (Maven to Gradle, Webpack to Vite, CRA to Next.js, npm to pnpm), API migrations (REST to GraphQL, REST to gRPC, SOAP to modern interfaces), authentication modernization (legacy to OAuth/OIDC, SAML/SSO), monorepo consolidation (Bazel, Nx, Turborepo), and testing framework migrations.
- 4Strong understanding of compatibility, testing, observability, staged rollouts, rollback strategies, and behavioral equivalence.
- 5Ability to reason through unfamiliar codebases and pinpoint subtle migration failures.
- 6Experience modernizing mission-critical systems in banking, payments, trading, insurance, healthcare, telecom, or similar sectors.
- 7For COBOL/mainframe roles: familiarity with z/OS, CICS, JCL, DB2, VSAM, batch processing, and COBOL-to-Java/Python migrations.
Who Should Apply
The candidate who fits this role has personally led or played a major role in large production migrations and can speak to specific challenges like preserving data integrity and handling rollbacks. Someone with only greenfield development or small-scale refactors will not find the work here. A common reason for rejection is failing to show concrete examples of migration ownership, especially in high-reliability domains like banking or telecom. Candidates who cannot articulate how they validate behavioral equivalence or manage regression risk during phased rollouts often score low.
Salary Insight
Pay is $200 per hour, a rate that aligns with the senior or principal-level ownership this role expects. Because the engagement is part-time, actual monthly earnings depend on hours agreed, and ongoing work may open up as the research program expands.
Location
Required Skills
Application Tip
In your application, describe one production migration you owned end to end, including the legacy stack, the target stack, how you staged the rollout, and how you detected regression. Quantify the system size and any downtime or rollback events.
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1Application received
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2ATS + eligibility screening
We check your profile against the role’s skills, seniority, and requirements.
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