I’m hatappi, working on SRE & Enabling at Cross Border (XB) Engineering. In addition to our SRE role, our team also serves as an Enabling team as defined in Team Topologies, supporting (enabling) XB developers to deliver value more smoothly through technical problem-solving and environment optimization.
In July 2025, I transferred from the Platform Network team to the XB SRE & Enabling team, where my first assignment was working on the launch of Mercari Global Web. This article, as part of the Behind the Scenes of Developing Mercari’s First Global App, “Mercari Global App”, focuses on the Global Web being developed alongside the app, and introduces the approach I’m practicing to deliver value as an SRE in this new environment.
Approach to Problem Discovery for Enabling
When I transferred to the XB SRE & Enabling team in July, my first mission was "enable the launch of the Global Web." However, having just transferred, I didn’t know what challenges or improvement points existed. I believed that correctly understanding the current situation was essential, so I took two approaches.
1. Trying It Myself
To understand and empathize with the challenges Global Web members face, the quickest way is to experience it myself. Therefore I tackled one feature development task. This allowed me to experience not just setting up the local environment and checking operations, but the entire development cycle from implementation, creating a pull request, receiving reviews, to merging.
Through this approach, I identified various improvement points including CI execution requiring long wait times for feedback and local dev server startup being slow.
2. Listen to Voices
Relying solely on your own experiences inevitably narrows your perspective. It’s particularly important to hear from members who develop the Global Web as their daily work. I gathered information by asking about improvement points on Slack and participating in planning and retrospective meetings.
This not only identified issues I couldn’t discover alone but also helped me in prioritizing them. For example, while I identified slow CI execution time as an improvement point, in reality CI execution time only became concerning at the final stage when it was necessary to receive reviews from other members. The instability of CI caused by occasional failures and slow local server startup times were perceived as bigger challenges.
Insights Gained from Platform Engineering Experience
While implementing these two approaches, I had the opportunity to reflect on my previous experiences with the Platform Network team.
As part of the Platform Network team, we provided shared infrastructure and tools that could be horizontally deployed across multiple Mercari products as part of Platform Engineering. Mercari has multiple products, each with its own unique context and domain knowledge. This presented a challenge, as it was difficult for the Platform side to deeply immerse itself in and fully understand the specifics of every product’s environment.
Through the implementation of the two approaches as a member of XB’s SRE & Enabling team, I have come to re-recognize the importance of deeply engaging with the field. At the same time, my experience in Platform Engineering has also helped me understand the significance of horizontal deployment when considering Mercari as a whole.
At Mercari, there are still not many engineers who have experience in both areas. That is precisely why I am actively providing feedback to the Platform team based on the experiences I have gained at XB, such as the recent improvements related to the global web, and working together to drive improvements forward.
Problem Solving Utilizing AI
In the previous section, those two approaches greatly increased the resolution of issues to tackle. However, having just transferred, knowing what to improve was not enough. I still needed to catch up on much information including Global Web and Cross Border contexts, as well as Web-related technologies. To smoothly enable the Global Web launch, I attempted to streamline this process by leveraging AI.
Learning and Research
For example, let’s say we’re tackling the issue of slow CI execution time. To understand this, I first need to understand how it works. As explained below, I considered necessary information and improvements while utilizing Claude and Claude Code.
First, I used Claude Code to investigate existing CI-related configurations. Since Mercari uses GitHub Actions, I asked about Action purposes and confirmed dependencies between Jobs while reading the source code to deepen my understanding. During the research, I encountered technologies I wasn’t familiar with, such as Turborepo.
When encountering unfamiliar technologies, I read the official documentation as the primary source to understand them. I utilized Claude for summarizing documentation. While Claude Code could be used directly for this, I chose Claude for its Artifacts feature (Fig1). Artifacts is a feature for creating independent content that can be created and edited during conversations with Claude. This allows me to deep-dive into unfamiliar technologies while creating comprehensive documentation that’s easy to reference later.
Fig1: Claude Artifacts
The final step was research for improvements. As a first step in considering improvement methods, I utilized Claude Research to collect general improvement strategies. For example, "Research common methods to speed up CI in the repository using Turborepo." This allowed me to efficiently list multiple approaches such as improving cache strategies and optimizing parallel execution in a short time, enabling efficient hypothesis formation for improvements. Additionally, using Artifacts, I could compile information toward final implementation based on the research findings.
Implementation and Review
Once improvement hypotheses are established, the next step is implementation. The information compiled during research exists in Artifacts and can be output as Markdown, which can be used with any tool or model such as Claude, GPT, or Gemini.
I primarily use Claude Code because of Slash commands. Slash commands are special commands starting with / in Claude Code that can execute specific operations. I’ve migrated processes I perform during development to these Slash commands. For example, there’s a Slash command for creating pull requests from changes. This Slash command defines not just pull request creation but also steps I frequently perform, such as considering commit messages from changes and committing.
After implementation comes review. While I have Claude Code review as well, I also perform reviews myself. Previously, I used git diff or diff viewers attached to editors. However, I often found improvement points when creating pull requests on GitHub that I thought were fine during local review. Making changes and pushing every time to check on the pull request takes time. To solve this problem, I started using difit.
difit is a CLI that provides GitHub-like views in the local environment (Fig2). As it’s added as an npm package, installation is simple and you can start using it immediately. With GitHub-like views, I can now do locally what I used to do on pull requests. Additionally, difit has a comment feature with copy functionality that allows added comments to be passed as prompts to AI. Thanks to this, the cycle of developing with Claude Code while reviewing and improving can now be completed locally.
Fig2: difit (https://github.com/yoshiko-pg/difit)
Debugging
Finally, debugging. I usually use Chrome. Chrome DevTools is indispensable for debugging. However, with its various features, I always struggled with which features to use and where to look to find the information I needed.
Therefore I tried the recently released Chrome DevTools MCP. This feature extracts necessary information by operating DevTools through an MCP Server with just natural language instructions. For example, just entering "Check the performance of this Global Web page" analyzes relevant metrics.
This allowed me to smoothly perform DevTools operations that I previously struggled with, reducing the time to problem discovery.
Learnings from Enabling Activities
I learned two things through this Global Web enabling experience.
The Importance of Entering the Field and Engaging with Primary Information
The first is the importance of being in the frontline and accessing primary information. If I had made judgments based only on objective metrics, it would have been difficult to notice that occasional CI instability and local server startup time were bigger problems than the CI execution time that development members were feeling.
The Effectiveness of AI When Challenging New Technology Areas
The second is that AI lowers the barriers when challenging new technology areas.
Even understanding the importance of the first approach, hesitation occurs if the hurdle to practice is high. However, I felt that utilizing AI made it easier to overcome this "initial wall." Of course, AI doesn’t solve everything, but I feel that my preferred approach of first creating something that works and then deeply understanding its mechanisms can now be done more smoothly.
Future Work
As mentioned in Rebuilding App and Foundation for Global Expansion, expansion to 50 countries and regions is planned within the next three years, which is technically very challenging. To expand globally at this speed, there are many things to consider: what implementation and settings are needed, how we can optimize efficiency, where to place data, where to locate web servers, and how we can utilize CDN. Because there’s so much to consider, it’s interesting and I feel it’s where SRE & Enabling can really shine, so I’m very excited about it.
Conclusion
This article introduced how I’m advancing Global Web Enabling in a new environment after transferring from the Platform Network team.
On November 13, 2025, Mercari Group’s tech conference "Mercari GEARS 2025" will be held. I’ll be talking about the CDN migration I worked on when I was in the Platform Network team. There are many other interesting sessions, so please join us!
Register here 👉 https://gears.mercari.com/
Tomorrow’s article is by @gia. Please continue enjoying the Behind the Scenes of Developing Mercari’s First Global App, “Mercari Global App”.
