Software Engineer, Backend (foundation) - Mercari Marketplace

• Location: Minato City, Tokyo, Japan (Hybrid)
• Employment Status: Full-time
• Work Hours: Full Flextime (no core time)
• Office: Roppongi

Description

The Foundation Backend team builds and operates the core business services that nearly every part of Mercari depends on, including notifications, user settings, and media. These are high-throughput, business-critical systems written in Go on Google Cloud Platform. Our work ranges from day-to-day reliability and support of these services to large company initiatives such as platform globalization, growth-related initiatives, marketing campaign improvements, enabling agentic SaaS-like experience for core services, and modernization and rearchitecturing of legacy systems. We keep the foundation stable, scalable, and evolving so product teams can move quickly on top of it.

Work Responsibilities

• Develop, maintain, and operate backend services in Go across the Foundation domain (notifications, user attributes, media).
• Investigate and resolve operational support and inquiry tickets raised by internal teams and Customer Support, improving reliability and reducing recurring toil.
• Join the on-call rotation after onboarding to support incident response for Foundation services.
• Contribute to platform initiatives such as the global rollout, growth-related initiatives, campaigns, enabling agentic SaaS-like experience for core services, modernization and rearchitecturing of legacy systems, and more.
• Write tests and documentation, and participate actively in code reviews.
• Proactively identify improvement opportunities in the team's services, code, and operational processes, and drive them through to implementation.

Unique Challenges

• Foundation services are used by almost all of Mercari; changes demand strong attention to reliability, scale, and backward compatibility.
• Balancing a meaningful operational/support load alongside feature and migration work requires good prioritization and communication.
• Contributing to a large-scale data migration that touches core user and notification data.
• Operating core services at very high volume such as notifications across various types and channels (InApp, push, email, SMS/Voice), where fan-out, delivery reliability, all have to load up under load.
• Working across several distinct domains and maintaining enough operational familiarity with each service to support and run all of them.

Qualifications

Required Experience/Skills

• Backend software development experience (Go preferred; strong experience in another server-side language with the willingness and ability to learn Go).
• Solid understanding of designing, building, and operating web services / APIs.
• Familiarity with relational databases and SQL.
• Experience working in a cloud environment (GCP preferred) with containerized deployments.
• Operations experience with on-call and customer support.

Preferred Experience/Skills

• Experience with distributed systems and microservices at scale.
• Experience with messaging/notification systems (push, email, SMS).
• Exposure to Google Cloud Spanner or large-scale data migrations.
• Experience with gRPC / Protocol Buffers and Kubernetes.
• Experience with CloudFlare Streams/Images.
• Experience with Amazon S3 and SES.

Language

• Japanese: Welcomed but not required
• English: Business-level, working proficiency