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Hansel Notes

About

Hansel Susanto

Software engineer · Tokyo, Japan

Portrait of Hansel Susanto

I’m Hansel Susanto, a software engineer in Tokyo. By day I work on the LINE messaging app at LY Corporation (LINE Yahoo). On the side I run MTS Studio — a remote-first product studio I started in 2018 — and I’m building Incid, the studio’s next product, an on-call command center for engineers paged at 3 AM.

Work

A reverse-chronological list of the places I’ve worked.

  1. LY Corporation (LINE Yahoo) logo

    Software Engineercurrent

    LY Corporation (LINE Yahoo)·Tokyo

    On the Messaging team, building backend services in Java and Kotlin (Spring, Armeria) for LINE Yahoo Premium — features like extended chat retention — on a platform serving 200M+ monthly users across Japan, Taiwan, Thailand, and Indonesia. Most recently wired Premium into the internal billing platform, consuming in-app-purchase events to keep entitlements correct for 600K+ subscribers.

  2. MTS Studio logo

    Founderongoing

    MTS Studio·Remote

    A remote-first product studio I started in undergrad, building apps across EdTech, community platforms, and IoT.

  3. Stockbit logo

    Software Engineer

    Stockbit·Jakarta

    On the Transaction team at Indonesia's largest retail brokerage, owning balances, money movement, and stock positions. Architected the Kafka-choreographed order-execution pipeline — sub-10ms to the exchange, built to absorb the 1,000+ RPS bursts at every market open — and the margin-leverage order system behind $18M+ in daily traded volume.

  4. ByteDance logo

    Software Engineer

    ByteDance·Jakarta

    Led R&D on TikTok Shop's buy-now-pay-later payments across eight APAC markets — 1M+ users and $100M+ in monthly GMV. Most of my work was the idempotency and reconciliation layers that let payments survive partner outages, missed webhooks, and dropped events without ever double-charging anyone.

  5. Tokopedia logo

    Software Engineer

    Tokopedia·Jakarta

    Shipped the GoPay Pinjam open-market integration — it tripled cash-loan applications and added ~$50K in daily revenue — then integrated the in-house OneKYC SDK into GoPay Later, lifting approval rates 23% and cutting approval time to under five seconds.

  6. Lumina (YC W22) logo

    Software Engineer

    Lumina (YC W22)·Remote

    An early engineer at this YC-backed professional network for blue-collar workers. Designed a WebRTC live-streaming service for on-demand shows and trained an NLP spam classifier (92% precision) that cleared up the community feed.

  7. Tokopedia logo

    Software Engineer Intern

    Tokopedia·Jakarta

    Led a ten-service cloud migration to GCP that cut spend by $10K a month, and built core systems for the Tokopedia Card — a product that went on to reach 5M+ users and win Best Credit Card 2022 from The Asian Banker.

  8. Shopee logo

    Backend Engineer Intern

    Shopee·Jakarta

    Maintained the “Buy Voucher Get Coins” system and built a multiplayer game server in Go.

  9. Bangkit Academy logo

    Machine Learning Participant

    Bangkit Academy·Indonesia

    An eight-month machine learning program run by Google, Tokopedia, Gojek, and Traveloka.

What matters to me the most

A few principles I keep coming back to.

  • Magis.

    Latin for “more.” The Jesuit principle I grew up with: always do more, always do better, in service of something greater than yourself. The self-improvement engine that everything else here runs on.

  • Daily practice is the only true compounding asset.

    For me, that practice is the violin. Every day, even when I don’t feel like it.

  • The best engineering ideas come from outside engineering.

    Most of mine came from books that had nothing to do with software.

Get in touch

My inbox is open. I read everything and reply to most things.