Kengo Hamasaki

Kengo is an end to end web engineer from Japan. He codes for both client-side and server-side, and looks over infrastructure as DevOps. He is also a payment freak with expertise in credit card payment processing. Running some OSS projects and keep contributing to OSS 5+ years.

GitHub hmsk
Twitter hmsk
Facebook hamachang


Web/Mobile Development
Ruby / Ruby on Rails / Sinatra, TypeScript / JavaScript, RSpec / Minitest / Jest, Vue.js / Vuex / React / Redux, Nuxt.js / Next.js, Webpack / Rollup, ESLint / Storybook, ERB / Haml / Slim / Pug (Jade), Sass / Scss / LESS / PostCSS, HTML5 / CSS3, Angular, Node.js, Elm, RESTful API and Client
Backend Technologies
MySQL, Varnish, Fastly, Nginx, Google Cloud Platform, Amazon Web Service, Redis, Stripe (Payment)
Development Style / Culture
Test Driven Development, DevOps, ChatOps, GitHub Flow, Heroku / Heroku Flow, Continuous Integration, CircleCI


Indiegogo, Inc.

Senior Software Engineer Apr 2017 - Present
  • Update the payment related system and user interfaces to follow new eKYC requirements with updating Stripe Connect usage
  • Automated dependency updates of the frontend stack with Dependabot, define the workflow and spread for all developers to keep the tech stack modern
  • Updated Indiegogo's payment flow to support Strong Customer Authentication aka, 3D Secure using Stripe. Replaces 'Charge', 'Token' based usage with 'PaymentIntent' and 'PaymentMethod'.
  • Published OSS: vuex-module-validatable-state, which provides handy form handling logic to Vuex state.
  • Created the Indiegogo's design system with building reusable Vue components. Moreover, documented their specifications and building guidelines, design principles to share with the entire product team by Storybook. 50+ shared reusable components are registered in a year.
  • Published OSS: vue-sfc-analyzer-webpack-plugin, which evaluates Vue + Webpack project's analysis.
  • Built fundamental development environments for Vue.js, with TypeScript, Vuex, vue-class-component, Jest, ESLint, Stylelint, and Webpack. This replaces Indiegogo's stale frontend stack by AngularJS 1.x.
  • Ran evaluation of the modern frontend technologies from Angular, Elm, React, and Vue for the whole development team. Additionally, investigated some building systems such as Rollup, Webpack, and Parcel.
  • Built the server-side-rendering logic for the front-end framework which was non-native for SSR and caching system to improve the performance of the website with Node.js, AngularJS and Fastly.
  • Continuously, keep working on the feature development of involving many reviews for other developers on the team.
  • Made the most number of commits to our main repository in 2018 among all developers. The most involved reviewer for Pull Requests in 2018, 2019.

Indiegogo, Inc.

Software Engineer Aug 2016 - Mar 2017

Indiegogo is the place for entrepreneurial projects to move quickly from concept to market, amplified by a community of backers who believe the world benefits when every idea gets an equal shot at success.

  • Built user-facing features with Ruby, Ruby on Rails, TypeScript and AngularJS.
  • Built a system which handles banking/identity information of merchants who are from all over the world with Stripe Connect.

WebPay, Inc.

Software Engineer / VP of Product Development Nov 2012 - Aug 2016

WebPay is a startup that offers credit-card payment gateway with developer friendly API and SDKs. The company is acquired by LINE in 2015.

  • Built RESTful API service which is compatible with Stripe API from scratch with Ruby on Rails, Delayed Job, MySQL, HAML, Sass, and Bootstrap
  • Built Ruby, Android, and JavaScript SDKs for external developers who use WebPay
  • Built secure credit card payment form with JavaScript and design its UI/UX like Stripe.js as of today
  • Automated many manual operations with regard to credit-card payments: account activation, billing, and fraud resolution, disputes, and chargeback
  • Managed product development of whole services
  • Supported many customers/developers who build their web application using WebPay
  • Kept highly security level of as credit card payment service (PCI DSS Level 1)

Cookpad, Inc.

Software Engineer / Infrastructure Engineer Apr 2010 - Oct 2012

Cookpad runs the biggest cooking recipe sharing service.

  • Operated highly available and heavy traffic web infrastructure
  • Replaced the content delivery system with Varnish caching, by which improving availablity and response time remarkably
  • Built features for users who publish cooking recipes on
  • Built simple framework which provides a JavaScript API for native Android interfaces
  • Built and released two Android applications, one of which has over 5 million downloads on Google Play in 2012

Hatena Co., Ltd.

Infrastructure Engineer Apr 2008 - Mar 2010
  • Operated 500+ physical linux servers in data center and 1000+ virtual linux servers with Xen
  • Built RPM packager with resolving CPAN dependencies
  • Designed original chassis for server, based on Hydrodynamics



Organizer (2014, 2018, 2019), Staff (2015, 2016, 2017), Helper (2010, 2011, 2013) Aug 2010 - Present

RubyKaigi is an annual conference for Ruby programmers in Japan.

  • Setup and helped run the conference
  • File and apply for speakers and attendees visiting the conference
  • Built and operated the digital signage system with Node.js, Heroku, and Android (2014), EmberJS and Firebase (2016), Nuxt.js and Firebase (2018)
  • Manage inquiries from overseas attendees and sponsors
  • Work on making documents to apply the visa for attendees who visits Japan from overseas


Graduate School of Electro-Communications

Apr 2009 - Mar 2011
Master (Not obtained nor graduated) - Engineering

University of Electro-Communications

Apr 2007 - Mar 2009
Bachelor - Engineering

Kitakyushu National College of Technology

Apr 2002 - Mar 2007
Associate Bachelor - Engineering


Meguro-kai Prize
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President of University of Electro-Communications

Excellent achiever among the graduates.


見落とされているApple Payの本当の価値 - What ApplePay really means
Techcrunch Japan

Guest post on Apple Pay's business structure with regard to credit-card system for Japanese.

Web決済入門 - Web payments first guide for Web developers
Gijutsu-Hyohron Co., Ltd.

Featured article about Web payments. Gihyo is a magazine for Web developers in Japan. Detailed explanation of payment methods and credit-card payment systems and tutorials on how to integrate WebPay, PayPal, Apple In-App Purchase, and Google Play In-App Billing.

ウェブオペレーション - Web Operations
O'Reilly Japan, Inc.

Guest post on backend infrastructure of to the Japanese translation of Web Operations from O'Reilly Media.


English (Working proficiency)
Working proficiency


Kengo is an extremely thoughtful, hard-working engineer with in-depth experience in full-stack web development and build systems. At Indiegogo, Kengo took a leadership role in maintaining and modernizing our JavaScript stack, eventually leading the charge for our transition from AngularJS to Vue.js. Kengo wrote most of the foundational code for the Vue infrastructure and build system and pioneered a component library and design system that brought designers and developers even closer together. Kengo has a very close pulse on the latest developments in the JavaScript community and is constantly trying out new things in his spare time. He is also very involved in the Ruby community and has a strong grip on architectural best practices and object-oriented design patterns. He provides very deep feedback during code reviews and writes the best pull request descriptions I've ever seen. I would love to work with Kengo again, and any team would be lucky to have such a talented, passionate individual.
— Siena Aguayo (Co-worker at Indiegogo, Inc.)
I had the absolute pleasure of working with Kengo for almost three years. Over the course of those years, I saw the true breadth of his performance as an employee and the staggering depths of his knowledge as a software engineer. Kengo led several key initiatives that would seem daunting to even the savviest of engineers; however, his experience as a seasoned technician and his admirable commitment to collaboration carried him through these initiatives seamlessly. Everything that I know about effectively developing and maintaining front end architecture, I learned from him, and I consider myself incredibly lucky for that fact. Kengo would be a huge value add to any team fortunate enough to welcome him; I earnestly give him my highest recommendation.
— Mike McGowan (Co-worker at Indiegogo, Inc.)
I've known Hamasaki-san for about 2 years now, his hard work on RubyKaigi and job are repeatedly visible. I always see him carrying a laptop, and when he stayed with me last year, for 2 weeks all he did was work.. and eat ramen. I'm confident that if I recommend hmsk for any job he would work his hardest no matter what it is.
— Zachary Scott @_zzak (Ex-Roomate, Co-Staff of RubyKaigi)
I worked closely with hmsk at WebPay and highly recommend him. I saw him lead product development, support customers, and handle account activation. He was the most critical member at our team, and without him, our company and product wouldn't have accomplished the same growth. He designs using css, writes clean code in ruby and javascript, and looks over the servers.
— Yohei Okada (Co-worker at WebPay, Inc.)