Masato Ohba (ohbarye) CV

Last updated: 2020.06.05

Japanese version:


key value
Name Masato Ohba (大庭 直人)
ID ohbarye
Email over.rye+jh [at]


The core of my strength is web backend. I have experience in full-cycle development for both in-house development and client work. I can be the overall lead in the team from development to operation, starting with the requirements and requirements definition, which is done with timely communication.

I have been developing SPA and MPA with React in the System of Engagement areas such as registration leads and retention measures, and in the Web frontend area for services that require rich experiences.

I can develop complex business logic required in the System of Record fields, such as payment functions and internal systems, with quality, speed, and robustness in mind.

I also served as an engineering manager for an organization with 20-60 engineers. As a result, I have a proven track record and knowledge of team design, project management, recruitment, corporate branding, culture building, community activities, and more.


Bold indicates core skills.

* denotes a skill that has no work experience, or has work experience but is more than a few years away.


Design and implementation in consideration of operation and performance

I have experience in designing and implementing designs that not only temporarily meet business requirements, but are also aware of performance, computational complexity, and data growth over time. In addition, I have performed performance tuning for problems that happened during the operation.

Batch processing, retry, data integrity in payment systems, and how developed functions to be operated. I’m confident in designing, developing and reviewing in consideration of these.

Leverage and improve OSS

Although it’s nothing special in this day and age, I use OSS in work. When I select a technology, I focus on whether the technology is feasible as a team, as well as convenience and trends, and I also consider sustainability and disposability. I often make conservative choices as a result of prioritizing the productivity of a team. I’ve been using SaaS like dependabot for libraries that my product depends on, and I’ve been upgrading the dependencies periodically

In addition, I believe that products I develop and OSS are connected to each other. If OSS doesn’t have a necessary feature, I try to develop it by myself, send patches, and fix bugs and regressions when I notice them. (OSS contribution by me is also described in the Personal Projects and Public Output sections below.


I have a keen interest in achieving results as a team and have worked to create mechanisms and foster a culture where collaboration can occur. As a manager, I also have experience of determining team assignments by considering variables such as strengths, weaknesses, orientation, and business characteristics.

In the past, when my team has had process issues, I have implemented Scrum to “clarify goals”, “be accountable”, and “prevent overwork”, and I have even taken on the role of a scrum master.

Problem solving in engineering organizations of up to 60 people

As an Engineering Manager in an organization with 20-60 engineers, I have experience in organizational design, team design, recruiting, mentoring, onboarding, culture building, and community activities.

Issues that arise when a team or organization grows in size are often the first ones experienced in that organization. Therefore, without clear identification of the true cause and prioritization and assignment, it is often left unchecked and distortions are magnified. I believe that my experience in knowing and dealing with these characteristics of organizational issues can be applied to teams and organizations of the same size or dozens of people, whether my role is as a member or manager.


I try to summarize what I’ve researched and learned through my hobbies and work and output it. Repeating output-conscious contemplation and trials can hone my skills in abstraction and commonalization. Moreover, I believe that it is possible to enhance the overall ability to find and solve problems.

I’m not very good at having presentations. However, I challenge it as possible as I can for feedbacks I’d get and thing I’d learn through those opportunities. Please refer to the Public Output section for the results.

Weakness / I’ve never done that before.

I can play to the above strengths in product development with monolithic applications on the backend and in teams of a few to 20 engineers, but I have little or no experience with the followings.

  • Microservices, distributed systems
  • Huge scale traffic
  • Mobile App Development
  • Architecture design and infrastructure as code (Terraform, Ansible, etc.), and using Cloud services (AWS, GCP, Azure, etc.)
  • Selection, operation, and tuning of middlewares.
  • Hardware and embedded software
  • Development in a large team of over 20 people

I am motivated to learn in areas where I have no experience. I think it’s possible because I’ve done some catch-up in the past on the technology needed for the job.

Work Experience

Quipper Limited (2015.09 ~ 2020.05) 4 yrs 8mos

Quipper is a company that operates both B to C and B to B education businesses. We develop and operate Quipper School and Quipper Video outside of Japan, and StudySuppli in Japan.

Under the umbrella of the Study Supplements brand, there are courses for elementary, junior high, and high schools, English for working adults, and forSchool for schools and municipalities. Some of the projects I was involved in are listed below.

Title Period Appeal Points
Code cleanup 2020.03 Toughness to remove huge amount of codes
Price Change 2019.10~2020.01 Payment systems, complex business logics
Migration from React Native to PWA 2019.07~2019.09 Technology selection, paying back technology debt
Develop Coaching Service for Junior High School Students 2018.08~2019.03 9 people x 7 months project management / Scrum
Entry Form Renewal 2018.03 Technology selection、EFO
Upgrade grape gem 2017.10~2017.12 Paying back technical debt, OSS
Develop Coaching Service for High School Students 2016.12~2017.02 Short term development
Benkyo Sapuri Migration 2016.06~2016.12 Short term development
Hiring 2016.07~2020.03 Organization design
Develope In-App Purchase for iOS 2016.04~2016.06 Payment systems, OSS
Jyuken Sapuri Migration 2015.09~2016.02 Short term development, catch-up tech stacks
Other Activities - Continuous improvement

Code Cleanup

Because out team’s monorepo, which used to share code across multiple products, has been forked, a lot of our code base got unused. I thought that cleaning up those dead codes would bring better development experience, so I almost single-handedly suggested and executed code cleanup.

It took about three weeks to remove 400,000 lines of code, and the removal of unused models in Rails was able to reduce the number from 390 to 281. I made significant changes to the system in operation, but completed them without causing a failure that would affect the end-users.

Period Team Role Tech stacks, tools
2020.03 1 (Web×1) Web Ruby, Rails, React, Redux, TypeScript (Deletion Targets)
NewRelic, BigQuery (Usage research)

Migration from React Native to PWA

This project is a renewal of an iOS/Android business internal app made by React Native with PWA. I was primarily responsible for the launch and backend of the project. (The UI/UX was revamped at the time of the relaunch, so the backend had to be changed as well.)

Since there was no mechanism to share the API specification before the project, I wrote the API specification using OpenAPI and laid the groundwork for sharing it. And leveraging Rack middleware, which only works in an automated testing and staging environment, I also put in place a mechanism to detect specification violations. (I wrote more about it in a blog post.)

I also made a presentation at JSConf 2019 as a recap of this project.

Period Team Role Tech stacks, tools
2019.07~2019.09 6 (PdM×1, Designer×2, iOS×1, Frontend×1, Backend×1) Backend Ruby, Rails 5.0, RSpec, React 16.12, Redux 4.0, TypeScript 3.7, Cypress

Develop Coaching Service for Junior High School Students

In a highly uncertain project with over 10 new members in the majority and a size of over six months, I was able to release it by implementing and practicing practices such as Scrum, MobPro, 1-on-1, etc. And while it’s difficult to quantitatively evaluate it, it has led to the growth and retention of our members.

I have summarized the details of this project in “[How to Combat Uncertainty in a Large Project with Many New Members]” (

Period Team Role Tech stacks, tools
2018.08~2019.03 12 (PdM×1、Designer×1、iOS×1、Android×1、Web×8) Web, Scrum master Ruby, Rails, React, RSpec, Capybara, Redux, TypeScript, Jest, React Native

Entry Form Renewal

It is an EFO (Entry Form Optimization) project for the most important acquisition period in BtoC learning services.

  • I was responsible for both the front end and back end.
  • At that time, the majority of the team’s front-end work was MPA, and the entry form was implemented in Rails View and jQuery.
  • I selected Webpacker and React.
  • CVR of registration has been improved.
Period Team Role Tech stacks, tools
2018.03 3 (PdM×1, Designer×1, Web×1) Web Ruby, Rails, React, RSpec, Capybara, Redux, TypeScript, Webpacker

Upgrade grape gem

The biggest Rails API server in my company had been using a gem named grape, but the API hadn’t been updated since v0.12.0 in 2015 when it was introduced, so I upgraded it.

Compared to Rails upgrade, there is less information, and dependent libraries are sometimes dead, so I had to prepare a workaround to write a patch. Finally, I was able to upgrade to the latest version v1.0.1 at that time by gradually increasing the minor version (~v0.19).

As an aside, about a year after this, in December 2018, I had an issue with NewRelic not being able to get metrics for the Rails API. This was a problem on the NewRelic agent side, so I sent a patch to the upstream to solve it.

Period Team Role Tech stacks, tools
2017.10~2017.12 1 (Web×1) Web Rails 4.2, Ruby 2.4, RSpec, grape

Research to Abolish Payment Method

This project examines how much of an impact it will have on the business when it abolishes carrier payments, which have high fees and operating costs.

Using Optimizely SaaS, we were able to practice A/B testing and collect quantitative data while minimizing the amount of development and testing done by engineers.

I’ve written a blog post about this effort, and we’ve presented at events such as Rails Developer Meetup 2018 Day 3 and Regional Scrum Gathering Tokyo 2019.

Period Team Role Tech stacks, tools
2017.10 2 (PdM×1, Web×1) Web Rails 4.2, Ruby 2.4, jQuery, Optimizely


I made a full contribution, including document screening, first round, code testing, second round, casual interviews, and proactive participation in the referral lunch and referral dinner.

I also engaged in the following activities, which are closely related to our recruitment activities.

Period Team Role Tech stacks, tools
2016.07~2020.03 4~10 (Web×4~10) Web Rails, Ruby, minitest, React, TypeScript (For coding test)

Develope In-App Purchase for iOS

Our service was offering outright purchase feature within iOS app, but sales were not good, and there was a need to provide an auto-renewable payment function like credit cards.

I implemented server-side APIs and a batch process to check subscription statuses. During the development, I realized that venice, AppStore API client library used on the server side, didn’t support the automatic renewal, so I implemented it myself and sent a pull request. (The OSS is apparently short-handed, so I did several contributions even after that.)

I gave a presentation at iOSDC 2018 about the server side implementation of In-App Purchase, including the operation for that.

Period Team Role Tech stacks, tools
2016.04~2016.06 3 (PdM×1、iOS×1、Web×1) Web Rails 4.2, Ruby 2.3, RSpec, venice, AppStore

Jyuken Sapuri Migration

This is a project to rebrand the “Jyuken Sapuri” (Learning platform for high school students that our parent compary had used to run) on Quipper’s codebase as a “StudySapuri”.

There were not many technical difficulties, but it was insane project. We had to build a system that had originally been developed and operated for several years from scratch in six months.

I was in charge of a registration flow, batches to exchange data with external systems, student management functions for teachers, and automated homework delivery functions. Although I had none of experiences of tech stacks used in this project in the past, I was able to catch up in a short period and to finish my tasks.

Press release on this project:

Period Team Role Tech stacks, tools
2015.09~2016.02 10 (PdM×1、iOS×2、Android×2、Web×5) Web Rails 4.2, Ruby 2.3, RSpec, Capybara, Backbone.js, Marionette.js, Sion, Mocha, Chai

Other Activities

The followings are other regular and spot tasks I’ve addressed.

SCSK Corporation (2012.04 ~ 2015.08) 3 yrs 5mos

SCSK is a Japanese big information technology services company.

I was a member of a department developing some enterprise systems for real estate companies which needs better property management solutions. I’ve developed web applications for the purpose.

  • Web backend: Java6, Seasar2 (an open source web application framework)
  • Web frontend: jQuery
  • Web Server: Apache + Tomcat
  • DB: Oracle Database 11g

Public Output


Articles on Company’s Blog


Here are a few excerpts from All of them are in Japanese.

OSS Activities

Community Activities

  • Engineering Manager Meetup
    • Role: Meetup organizer
    • The purpose of this community is to share knowledge about engineering management, which is still not widely available in Japan.
    • In total, more than 500 people participated in the event.
    • I’ve been running it on my own for about 1.5 years.
    • I handed over the community management to the community.
  • EOF2019
    • Role: core member
    • The very first festival that puts “Engineering Management” on the theme in Japan.
    • Organize the OST session.
  • Meguro.rb (Ruby regional community)
    • Role: member
    • As an administrative staff member of Meguro.rb, one of the local Ruby communities, I hosted the event twice.

Personal Projects

These are artifacts of my personal projects.


It is a tool to make contribution to OSS easier. I thought that the biggest obstacle for beginners who want to start OSS contributions is to find the target of contribution, so I created a web service Goofi to list repositories and issues to which contribution is recommended.

At Nodefest 2018, I made a presentation about the service.

In January 2020, GitHub has published an official feature similar to Googi, then I took it as, "My recognition of the problem was right.

Period Repository Tech stacks, tools
2020.08~ Node.js 13.x, TypeScript 3.8, Next.js 9.1, GraphQL (client), v1~2 (現 Vercel), GitHub API v4

React Use Kana

This is a library to create a form that automatically inputs furigana when you type kanji. there are some libraries that have the same function with jQuery and similar libraries for older versions of React, but I couldn’t find a library that uses React hooks, so I made my own.

Period Repository Tech stacks, tools
2019 React 16.9, TypeScript 3.8.3

String Pixelater

A library that converts a character to a two-dimensional array of N * N dots. I was addicted to Processing at the time and implemented it through the process of creating Generative Art.

Period Repository Tech stacks, tools
2018 TypeScript 3.6.4, rollup 1.23

Review bot

It’s a Slack bot that encourages reviews in team development. It posts a list of pull requests to Slack that match specified conditions.

It’s similar to Pull Panda, acquired by GitHub in June 2019. But my bot was forked by some companies for their internal use, that’s probably because Pull Panda was not free.

Period Repository Tech stacks, tools
2017.08~ Node.js 8.x, GraphQL (client) Slack API, GitHub API v3~4, Heroku


This is a library that automatically generates HTML to preview email text when running tests with RSpec.

Period Repository Tech stacks, tools
2017 Ruby 2.4, RSpec 3

Markdown Server

This is a library that can build a web server to deliver Markdown documents as HTML. I made this for learning Python.

Period Repository Tech stacks, tools
2015 Python 3.7, bottle 0.12



Honors & Awards


By 2020, I have developed the technical skills required in the field of software engineering, especially in the application layer of web services development. In the future, I hope to deepen my general understanding of software through learning about whole computer science, algorithms, low layers and middleware in particular.