JD in Japanese follows. 英文の後に和文JDをご覧いただけます。
Senior Software Engineer, Agentic AI Platform - 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:
•Engineering Culture
The AI Platform team drives Mercari Group's transformation into an "AI-Native company" from the perspective of technical foundations. We design, develop, and operate shared AI infrastructure used across the company, including an LLM Gateway, MCP Gateway, and Agent Sandbox, and we also build the AI Agents that work alongside development and operations on the ground.
What we build is used in two ways. First, as services that every role—including engineers, designers, and PMs—uses directly in their daily work. Second, as shared building blocks that other engineering teams inside Mercari use to construct AI workflows tailored to their own domains. For the former, we create an environment where every role can demonstrate AI as a baseline skill, through developing AI Agents and running PoCs for AI SaaS. For the latter, we provide foundations with enough generality for other teams to extend on their own, and enough reliability for them to trust with real work.
Where a product team delivers customer value directly, we make other teams able to deliver that same value themselves. That is why we measure ourselves not by the number of things we have built, but by what the people using them became able to do. In this role, you will work as an enabler for AI-native development across Mercari Group while owning the shared AI platform it runs on: you build the mechanisms that let other teams work AI-natively, and you operate the production services those mechanisms depend on.
See here for more information about our mission and values.
Work Responsibilities
You will be responsible for designing, developing, and operating the technical foundations that enable AI adoption across Mercari Group.
•Design, develop, and operate the AI Platform: Design, implement, and operate shared AI infrastructure such as the LLM Gateway, MCP Gateway, and Agent Sandbox. These are production services the whole company depends on, so you own their operation—availability, security, and cost optimization—alongside the enablement work. Decide what to offer as company-wide infrastructure by weighing the range of teams affected, the impact on development as a whole, and system-wide risk.
•Build AI Agents and an execution platform: Develop AI Agents that work alongside development and operations, and build an execution platform that shifts the developer experience toward AI-native. Design on the premise that both humans and AI Agents are users: clear interfaces, documentation and metadata prepared in a form AI can interpret, guardrails implemented as code, and mechanisms that continuously evaluate quality.
•Own adoption and outcomes: Continuously measure whether the foundations you shipped are actually being used and how the development process changed for the people using them, and when adoption does not spread, identify the cause and see the improvement through.
•Promote company-wide AI adoption: Partner with business and product teams to embed AI-first workflows across the organization through AI SaaS PoCs and community operations. Operate company-wide shared repositories as innersource, responding continuously to pull requests from other teams.
Development Environment
•Infrastructure: Google Cloud Platform
•Languages: Go, TypeScript, Python, etc.
•Code management: GitHub
•Configuration management: Terraform
•Analytics: BigQuery / Looker
•Knowledge: Notion, Confluence, Linear
•AI development tools: Claude Code, Codex, Cursor, etc.
•AI/LLM development: Foundation model APIs, LiteLLM, etc.
Note: Technologies may differ depending on the area of responsibility.
Unique Challenges
•Enable every role at Mercari to work AI-natively: Enabling thousands of engineers, designers, and PMs to make AI a baseline skill, by building the shared foundations they build on top of and the agents they use in their daily work. Your impact is measured by what those teams became able to do without you in the room, not by the number of tools you shipped. You will work at a scale where you redefine how development is done across Mercari Group, not merely provide tools.
•Implement and operate a rapidly evolving AI tech stack at Mercari scale: Tackle advanced technical challenges by operating emerging stacks such as LiteLLM, MCP, and AI Agents safely and scalably in an organization of thousands—an initiative that is globally pioneering.
•Design foundations for the agent era: Design infrastructure, architecture, and operating models from scratch for a future where humans and AI agents collaborate, and build knowledge ahead of the industry. A rough edge that a person working by hand would simply overlook becomes a large difference in failure rate once AI Agents repeat the same steps at volume. Designing with that difference built in is territory where no established answer exists yet, inside or outside the company.
•Evolve the platform through collaboration with diverse stakeholders: Work with various internal organizations (Platform, Product, Security, etc.) to lead technology selection, standardization, and adoption.
•Develop and roll out services for internal developers: You can lead everything end-to-end—from planning internal services for Mercari engineers to supporting adoption. Rather than being only a "supporter," you are expected to proactively identify and solve problems as the person who best understands internal developers' pain points. Instead of answering requests one by one, or writing guidelines and calling it done, you own the whole loop: finding the problem that keeps recurring, turning it into a reusable mechanism, driving adoption, measuring what changed, and improving on it. That also means judging what is worth turning into a mechanism at all—weighing how many teams it affects, the critical path, and system-wide risk—and declining, with your reasoning, requests that cost a lot and help only one team. This role is not a reactive support desk that measures itself on response time, and not a gatekeeper that uses standards as a means of control.
•Work as a user of the platform you build: Use your own foundations in your own daily development, and join the teams that use them to understand their problems firsthand. Rather than imposing standards and processes as constraints, you can aim for a state where they get chosen because they are the faster way to get the work done.
Qualifications
•Required Experience/Skills
•Empathy with Mercari Group and each company's mission and values
•Experience designing, developing, and operating backend or platform/infrastructure systems for large-scale web services
•Production experience building applications with one of Go, TypeScript, Python, etc.
•Experience developing/operating managed services or SDKs for internal developers and improving developer productivity
•Experience designing and operating infrastructure on cloud platforms such as Google Cloud Platform (including Kubernetes, Terraform, etc.)
•Experience designing and implementing applications or platforms using Generative AI / LLMs
•Strong communication skills to collaborate with multiple stakeholders, lead technical decision-making, and drive projects forward
•Experience acting as the owner of technical quality in your area, making the case for medium- to long-term investments such as architecture, standards, and shared foundations in business terms, and driving them forward
•Ability to form hypotheses and make autonomous decisions in uncertain situations and execute effectively
•Someone who incorporates AI into their daily development work and reviews its output with their own judgment rather than taking it at face value
•Preferred Experience/Skills
•Experience developing/operating AI platforms such as MCP Servers, AI Agents, and AI agent execution environments
•Experience designing interfaces and implementing guardrails on the premise that AI Agents operate autonomously
•Experience designing evaluation methodologies for AI agents/LLM applications (e.g., defining evaluation criteria, building benchmarks, quantitatively validating quality through A/B tests, etc.)
•Experience improving development processes / harness engineering using AI development tools (Claude Code, Codex, Cursor, etc.)
•Hands-on experience in Developer Productivity / Platform Engineering / SRE
•OSS contributions and community activity experience
•Language
•English: Independent (CEFR - B2) (required)
•Japanese: Independent (CEFR - B2) (optional)
For details about CEFR, see here .
Learn More About Mercari Group
•Careers site: https://careers.mercari.com/en/
•Mercan: https://mercan.mercari.com/en/
•Social media: X / Linkedin
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 .
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