SEN LLC

I build small, focused tools and ship them open-source. Based in Japan 🇯🇵 with SEN LLC, working through a 100+ portfolio at sen.ltd/portfolio. Posts about TypeScript, AWS, and bugs that taught me so

Tokyo, Japan Joined on Apr 10, 2026 https://sen.ltd

Work

Engineer at SEN LLC

SEN LLC

Apr 11

A GUI Cron Builder — And Why Building Is Way Easier Than Parsing

#javascript #webdev #cron #devtools

4 min read

SEN LLC

Apr 11

A Bill Splitter Where Unit and Rounding Are Orthogonal (They Usually Aren't)

#javascript #webdev #ux #math

4 min read

SEN LLC

Apr 11

Converting Between Japanese Eras and Gregorian Dates — and Why the Boundary Days Matter

#javascript #webdev #i18n #tutorial

4 min read

SEN LLC

Apr 11

Writing Conway's Game of Life With Uint8Array and Canvas, Including a Gosper Glider Gun

#javascript #webdev #canvas #tutorial

4 min read

SEN LLC

Apr 11

50 Japanese Traditional Colors, Sorted By Hue — Because the Names Aren't Enough

#javascript #webdev #css #design

4 min read

SEN LLC

Apr 11

Every Time Format At Once: A Converter That Stops the Unix-Seconds-or-Milliseconds Dance

#javascript #webdev #datetime #beginners

4 min read

SEN LLC

Apr 11

A JWT Debugger That Never Sends Your Token Anywhere

#javascript #security #jwt #webdev

4 min read

SEN LLC

Apr 11

I Built a Side-by-Side Base64 / URL / HTML / Encoder and Finally Stopped Confusing Them

#javascript #webdev #encoding #beginners

5 min read

SEN LLC

Apr 11

UUID v7, ULID, KSUID — What's the Difference? I Implemented All Five

#javascript #uuid #webdev #tutorial

6 min read

SEN LLC

Apr 11

Writing a Regex Parser and Tree Visualizer in ~400 Lines of Vanilla JS

#javascript #regex #webdev #tutorial

5 min read

SEN LLC

Apr 11

Writing a TypeScript Type Inference Engine in 300 Lines of Vanilla JS

#typescript #javascript #webdev #tutorial

5 min read

SEN LLC

Apr 10

You Probably Don't Need a Timezone Library Anymore

#showdev #javascript #webdev #tutorial

5 min read

Forem

SEN LLC

Badges

Writing Debut

Skills/Languages

Currently hacking on

A GUI Cron Builder — And Why Building Is Way Easier Than Parsing

A Bill Splitter Where Unit and Rounding Are Orthogonal (They Usually Aren't)

Converting Between Japanese Eras and Gregorian Dates — and Why the Boundary Days Matter

Writing Conway's Game of Life With Uint8Array and Canvas, Including a Gosper Glider Gun

50 Japanese Traditional Colors, Sorted By Hue — Because the Names Aren't Enough

Every Time Format At Once: A Converter That Stops the Unix-Seconds-or-Milliseconds Dance

A JWT Debugger That Never Sends Your Token Anywhere

I Built a Side-by-Side Base64 / URL / HTML / Encoder and Finally Stopped Confusing Them

UUID v7, ULID, KSUID — What's the Difference? I Implemented All Five

Writing a Regex Parser and Tree Visualizer in ~400 Lines of Vanilla JS

Writing a TypeScript Type Inference Engine in 300 Lines of Vanilla JS

You Probably Don't Need a Timezone Library Anymore