Sefa Karabaş

Full-stack engineer on the Assessment Team, building assessment experiences for a platform serving 80M+ learners worldwide.

• Designed and built Domain Assessments, which now have more learners than full assessments, with no drop in full assessment usage
• Co-developed the Google-style Practice Test feature for the Grow with Google partnership
• Refactored the assessment service to Hexagonal Architecture, making it easier for developers to build on and to onboard new engineers
• Contributed to the migration from a monolithic architecture to microservices and microfrontends
• Building the assessment feature from scratch for the unified Coursera–Udemy learning platform, using an agentic, AI-assisted development workflow with Claude Code

Tech Stack: Kotlin, Django, React.js, GraphQL, gRPC, Amazon DynamoDB, MySQL, Datadog, Sentry

Full-stack developer on payment infrastructure for Turkish Airlines' financial systems. Joined in the project's third month; the team grew from 5 to 15 engineers.

• Helped build a Payment Facilitator (PF) service from its early stages; the service processes 200M+ TRY in daily payment volume
• Led the integration of the Merchant Registration System (İKS), onboarding Turkish Airlines and AJet as the first merchants
• Built and maintained reconciliation and settlement modules to keep financial operations accurate
• Integrated banking and payment partners, including Payten, Kuveyt Türk, and QNB, to support end-to-end payment flows

Tech Stack: Java, Spring Boot, React.js, Kafka, Docker, Kubernetes, CI/CD

Full-stack developer on the Payments Team for global social platforms serving tens of millions of users.

• Integrated global payment providers Rapyd, PayerMax, and Wise into a payment system supporting 50+ currencies
• Built and optimized pay-in and cash-out flows that let users top up and withdraw funds for in-app tokens

Tech Stack: Django, Node.js, Vue.js, AWS, Cloud Functions, Cloud Firestore, Docker, Jenkins, CI/CD

Backend developer on the Digital Channels & Insurance team.

• Developed and maintained Java and Spring Boot backend services for customer-facing digital banking applications

Tech Stack: Java, Spring Boot

Data Warehouse (DWH) project supporting commercial banking operations.

• Parallelized the jobs in an ETL pipeline, making it 10x faster
• Designed and implemented ETL processes with Oracle Data Integrator (ODI)
• Developed and optimized SQL queries on Oracle and MS SQL Server for business reporting and analytics

Tech Stack: Oracle SQL, MS SQL Server, Oracle Data Integrator

Rental platform that connects tenants with landlords and tracks rent.

• Designed and built the customer-facing application and the internal management system end to end
• Integrated the Paycell payment gateway to enable secure online payments

Tech Stack: Angular, React.js, Redux, Java Spring, Hibernate