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Senior Web Engineer (AI/LLM) - Mercari
- Employment Status: Full-time
- Work Hours: Full Flextime (no core time)
- Office: Roppongi
For more details, see the Overview of Our Positions section on our Careers site.
About Mercari
Circulate all forms of value to unleash the potential in all people
"What can I do to help society thrive with the finite resources we have?" The Mercari marketplace app was born in 2013 out of this thought by our founder Shintaro Yamada as he traveled the world. We believe that by circulating all forms of value, not just physical things and money, we can create opportunities for anyone to realize their dreams and contribute to society and the people around them. Mercari aims to use technology to connect people all over the world and create a world where anyone can unleash their potential. For more information about Mercari Group’s mission, see Mercari’s Culture Doc
Organization/Team Mission
Mercari Engineering Principles
Mercari Engineering Principles are a shared understanding that serves as the foundation of engineering beliefs and behavior at Mercari. The Engineering Principles are designed to complement the organizational identity (Mercari’s mission, values, and culture) from an engineering viewpoint.
These principles ultimately help us achieve Mercari’s mission by defining the ideal state we seek to realize in the long term.
- Passion For The Product
- Grow Together
- Solve Through Mechanisms
- Collaborate Openly
For more details, please see the following link:
The AI / LLM Team’s mission is focused on two core pillars, "building" and "enabling", delivering new AI-driven features and user experiences to maximize product-facing impact for Mercari's business. We do this both through independent initiatives owned by our team, as well as by horizontally collaborating with product and engineering teams across the entire organization.
As a Web Engineer, you will collaborate with ML engineers, backend engineers, designers, and other web/mobile feature teams to build AI-powered, high-quality, user-facing web experiences.
See here for more information about our mission and values.
Work Responsibilities
- Implement, maintain, and improve high-quality web features using TypeScript, Next.js, and modern web tooling.
- Collaborate with product managers, designers, ML engineers, and backend teams to define feature requirements and deliver polished user-facing functionality.
- Build modular, testable, maintainable frontend components and shared UI modules.
- Contribute to technical design discussions and propose architecture improvements for frontend systems.
- Integrate with backend APIs and incorporate AI/LLM-powered services into web experiences.
- Ensure high performance, accessibility, stability, and cross-browser compatibility.
- Participate in code reviews, improve engineering workflows, and contribute to documentation and best practices.
- Collaborate with the wider Client Engineering organization to strengthen Mercari’s web platform and frontend foundations.
- Stay current with modern web technologies, frontend performance techniques, and UI/UX best practices.
Unique Challenges
- Develop AI-driven web features that leverage Mercari Group’s large-scale data assets and affect tens of millions of users.
- Deliver performant and reliable experiences in a fast-paced environment with complex product and technical constraints.
- Bridge cutting-edge AI capabilities with intuitive, accessible, consumer-grade user experiences.
- Work across multiple teams and domains to shape Mercari's AI-enabled product foundations.
- Operate in ambiguous problem spaces where user needs and technical trade-offs must be balanced.
Qualifications
- Required Experience/Skills
- Shared belief in Mercari Group’s mission and values.
- Bachelor’s degree in Computer Science, Engineering, or equivalent practical experience.
- Solid, hands-on experience with Next.js, TypeScript, and modern frontend ecosystems.
- Understanding of component-driven architecture, state management patterns, and modern frontend build tools.
- Experience integrating with backend APIs and handling asynchronous programming patterns.
- Strong problem-solving skills and comfort working with ambiguous requirements.
- Effective communication skills and ability to collaborate cross-functionally.
- Passion for building polished, user-centric web products.
- Preferred Experience/Skills
- Experience working on large-scale apps serving millions of users.
- Experience with performance tuning, profiling tools, and frontend observability.
- Familiarity with modern web frameworks (Next.js, Vite), React Server Components, or micro-frontend architectures.
- Experience working with design systems or creating reusable UI component libraries.
- Understanding of accessibility (a11y) best practices and internationalization.
- Experience contributing to cross-team technical initiatives or platform-level improvements.
- Language
- Japanese: Independent (CEFR B2) Optional
- English: Independent (CEFR B2) Required
For details about CEFR, see here.
Learn More About Mercari Group
Recruiting at Mercari
At Mercari Group, we value empathizing with and embodying the mission and values of the Group and each company. To promote the creation of an organization that maximizes the total amount of value exhibited by all members, we would like to understand the experience and skills of each candidate as accurately as possible.
Recruiting cycle at Mercari Group
- Application screening
- Skill assessment: For engineering positions, you will be asked to complete a skill assessment on HackerRank or GitHub. For non-engineering positions, you may be asked to complete an assessment depending on the position. (The timing of the assessment may coincide with the interview process.)
- Interview: The number of interviews may vary depending on the position.
- Reference check: We will ask for online references around the timing of the final interview.
- Offer: Offers will be determined carefully in consideration of the final interview and the reference check.
Learn more about our recruiting process here.
Equal Opportunity Hiring
Here at Mercari, we work to realize a world in which no one’s potential is limited by their background and everyone has the opportunity to freely create value. We also firmly believe that a mindset of Inclusion & Diversity is essential for us to achieve our mission.
This, of course, extends to our hiring practices as well. Mercari is committed to eliminating discrimination based on age, gender, sexual orientation, race, religion, physical disability, and other such factors so that anyone who shares our mission and values can join us, regardless of their background. For more details, please read our I&D statement.
Please read and acknowledge our Privacy Policy prior to submitting your application.
