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Mercari

Peer-to-peer mobile marketplace for secondhand goods

Software Engineer (AI Agents) - Internal

AI Application EngineeringConfirmed live in the last 24 hours
Full-timeMinato City, Tokyo, JapanNo salary listed

About the Job

Requirements

  • Lead specification refinement and stakeholder alignment, and take end-to-end responsibility through production release and subsequent operations.
  • Use AI-assisted development tools such as Claude Code at a professional level, critically evaluating, correcting, and integrating AI output while balancing speed and quality.
  • Rapidly build prototypes and use working demonstrations to finalize specifications.
  • Independently make technical design decisions involving architecture, APIs, data, security, and operations, and explain trade-offs in business context.
  • Work across backend, frontend, data, quality assurance, and adjacent disciplines, independently ramping up in unfamiliar areas using AI and documentation.
  • Be willing to mentor and coach colleagues and be motivated by organizational growth.
  • Have proficient Japanese language ability (CEFR C1).

Responsibilities

  • Identify business-process problems and design, implement, introduce, and operate AI agent solutions across Mercari Group processes.
  • Gather information and analyze business processes, demonstrate working prototypes to stakeholders, and lead specification development.
  • Lead design and implementation of generative AI systems and integrations with internal systems and SaaS tools.
  • Design events, logging, dashboards, and agent evaluations; establish quality criteria and rollout plans.
  • Make architectural, API, data, security, permission-management, and operational decisions and move work forward by explaining trade-offs in business context.
  • Lead post-release adoption, outcome measurement, and continuous improvement in collaboration with business teams.

Desired Qualifications

  • Have experience designing evaluations for AI agents or large language model applications, including evaluation criteria, benchmarks, or quantitative product-quality validation through A/B testing.
  • Have consulting or systems-development experience focused on improving or transforming business processes, including business interviews, requirements definition, or system and SaaS integrations.
  • Have experience launching products in small teams or leading development in an early-stage environment.
  • Have practical experience related to machine learning or data science.
  • Have independent English language ability (CEFR B1).

About the Company

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Mercari

Peer-to-peer mobile marketplace for secondhand goods

Mercari operates a mobile peer-to-peer marketplace for buying and selling secondhand goods. Users list items by taking photos in the app, and buyers complete purchases there, with payments held in escrow until receipt is confirmed. Revenue comes from seller fees (10% in Japan; 10% plus 3.6% buyer protection in the US), plus Merpay payments and promoted listings, plus shipping partnerships for integrated delivery. The platform differentiates itself through a simple mobile experience, escrow and buyer protection, shipping integration, and a broader marketplace including Mercari Shops for sellers, with a goal of extending product life and supporting a circular economy.

Company size
1,001-5,000
Company stage
IPO
Headquarters
Tokyo, Japan
Founded
2013

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