DEV Community

SEN LLC profile picture

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

Location Tokyo, Japan Joined Joined on  Personal website https://sen.ltd

Work

Engineer at SEN LLC

A Per-URL TODO List Chrome Extension in 150 Lines — Single-Key chrome.storage Design, URL Normalization, and Three Sync Paths for the Toolbar Badge
sendotltd profile

A Per-URL TODO List Chrome Extension in 150 Lines — Single-Key chrome.storage Design, URL Normalization, and Three Sync Paths for the Toolbar Badge

#chrome #javascript #productivity #webdev
1
Comments
5 min read
A 150-Line `whentime tokyo london ny` CLI in Rust — and Why You Need IANA tzdata, Not 'UTC + N'
sendotltd profile

A 150-Line `whentime tokyo london ny` CLI in Rust — and Why You Need IANA tzdata, Not 'UTC + N'

#rust #cli #productivity #devops
Comments
5 min read
Three Address Checksums, Three Engineering Philosophies — Verifying Base58Check, Bech32m, and EIP-55 in 250 Lines of Browser JS
sendotltd profile

Three Address Checksums, Three Engineering Philosophies — Verifying Base58Check, Bech32m, and EIP-55 in 250 Lines of Browser JS

#javascript #crypto #bitcoin #ethereum
Comments
6 min read
A 230-Line Chrome MV3 Extension That Copies the Page Selection as Markdown — Without `<all_urls>`
sendotltd profile

A 230-Line Chrome MV3 Extension That Copies the Page Selection as Markdown — Without `<all_urls>`

#chrome #javascript #webdev #productivity
Comments
6 min read
BIP39 in 180 Lines of Vanilla JS — Mnemonic Generation, Validation, Seed Derivation, and the Japanese Wordlist Trap
sendotltd profile

BIP39 in 180 Lines of Vanilla JS — Mnemonic Generation, Validation, Seed Derivation, and the Japanese Wordlist Trap

#javascript #crypto #security #webdev
2
Comments 1
6 min read
Why Your Web Audio Tuner Sucks at Low Notes (and What to Use Instead of FFT)
sendotltd profile

Why Your Web Audio Tuner Sucks at Low Notes (and What to Use Instead of FFT)

#javascript #webaudio #frontend #audio
Comments
6 min read
GitHub's Stargazers API Caps at 40,000. Here's How Star-History Tools Fake the Rest
sendotltd profile

GitHub's Stargazers API Caps at 40,000. Here's How Star-History Tools Fake the Rest

#github #api #javascript #dataviz
Comments
6 min read
A 3.7 KB Othello Engine: Bitboards in Rust, Raw WASM, No wasm-bindgen
sendotltd profile

A 3.7 KB Othello Engine: Bitboards in Rust, Raw WASM, No wasm-bindgen

#rust #webassembly #gamedev
Comments
6 min read
I Built a Japanese Poetry Quiz and the Web Speech API Showed Me Its Teeth
sendotltd profile

I Built a Japanese Poetry Quiz and the Web Speech API Showed Me Its Teeth

#vue #typescript #webspeechapi #japanese
1
Comments
5 min read
I Finally Understand the SVG d Attribute — Because I Built an Editor for It
sendotltd profile

I Finally Understand the SVG d Attribute — Because I Built an Editor for It

#svg #svelte #typescript #webdev
1
Comments
8 min read
I Put the Same Mandelbrot Kernel on the CPU and the GPU — and Watched float32 Crack
sendotltd profile

I Put the Same Mandelbrot Kernel on the CPU and the GPU — and Watched float32 Crack

#webgl #javascript #graphics #performance
Comments
6 min read
Why setTimeout Is a Bad Metronome — and What to Use Instead
sendotltd profile

Why setTimeout Is a Bad Metronome — and What to Use Instead

#javascript #webaudio #frontend #performance
Comments
5 min read
How Much Faster Is Rust/WASM Than JS for Image Filters? I Ran Both Side by Side and Measured
sendotltd profile

How Much Faster Is Rust/WASM Than JS for Image Filters? I Ran Both Side by Side and Measured

#webassembly #rust #javascript #performance
2
Comments
6 min read
A Cross-OS Port Finder in Rust — One CLI, Three Completely Different Data Formats
sendotltd profile

A Cross-OS Port Finder in Rust — One CLI, Three Completely Different Data Formats

#rust #cli #linux #networking
Comments
9 min read
A 300-Line GitHub Actions Security Linter: Five Rules That Catch the CVE Patterns
sendotltd profile

A 300-Line GitHub Actions Security Linter: Five Rules That Catch the CVE Patterns

#typescript #githubactions #security #cli
Comments
7 min read
A TLS Certificate CLI in Rust — No OpenSSL, No Ceremony, Just a Fail-the-Build Exit Code
sendotltd profile

A TLS Certificate CLI in Rust — No OpenSSL, No Ceremony, Just a Fail-the-Build Exit Code

#rust #cli #tls #monitoring
1
Comments
7 min read
CSV Sort, Done Right: Why `sort -t,` Is a Trap and What a 300-Line PHP CLI Does Instead
sendotltd profile

CSV Sort, Done Right: Why `sort -t,` Is a Trap and What a 300-Line PHP CLI Does Instead

#php #cli #csv #tutorial
1
Comments
9 min read
Reimplementing fd in 500 lines of Rust (and what I learned about the crates it stands on)
sendotltd profile

Reimplementing fd in 500 lines of Rust (and what I learned about the crates it stands on)

#rust #cli #filesystem #tutorial
1
Comments
10 min read
I Built a .env Diff Tool That Refuses to Print Values
sendotltd profile

I Built a .env Diff Tool That Refuses to Print Values

#typescript #env #cli #tutorial
1
Comments 1
10 min read
Writing a Regex Playground in 200 Lines of Rust
sendotltd profile

Writing a Regex Playground in 200 Lines of Rust

#rust #regex #cli #tutorial
Comments
9 min read
A 10 MB Markdown-to-HTML Service in Rust with pulldown-cmark
sendotltd profile

A 10 MB Markdown-to-HTML Service in Rust with pulldown-cmark

#rust #axum #markdown #tutorial
Comments
9 min read
git log --pretty is a tiny DSL: building a zero-dep CHANGELOG generator
sendotltd profile

git log --pretty is a tiny DSL: building a zero-dep CHANGELOG generator

#typescript #git #cli #tutorial
Comments
8 min read
Seed Data Without a Dependency Tree: A Tiny PHP CLI Instead of Faker
sendotltd profile

Seed Data Without a Dependency Tree: A Tiny PHP CLI Instead of Faker

#php #cli #database #tutorial
Comments
10 min read
sharp on Alpine Without Tears: a 260 MB Image Resize API in Hono
sendotltd profile

sharp on Alpine Without Tears: a 260 MB Image Resize API in Hono

#typescript #hono #sharp #tutorial
Comments
9 min read
Writing a tar Inspector in Rust with Three Dependencies
sendotltd profile

Writing a tar Inspector in Rust with Three Dependencies

#rust #tar #cli #tutorial
Comments
9 min read
A Tiny PHP Invoice-PDF API: Slim 4, dompdf, and the JPY Rounding Footgun
sendotltd profile

A Tiny PHP Invoice-PDF API: Slim 4, dompdf, and the JPY Rounding Footgun

#php #slim #pdf #tutorial
Comments
9 min read
Writing dig in 500 Lines of Rust (with hickory-resolver, the trust-dns successor)
sendotltd profile

Writing dig in 500 Lines of Rust (with hickory-resolver, the trust-dns successor)

#rust #dns #cli #tutorial
Comments
10 min read
Writing Cron Semantics in ~100 Lines of TypeScript
sendotltd profile

Writing Cron Semantics in ~100 Lines of TypeScript

#typescript #cron #cli #tutorial
2
Comments
8 min read
PHPStan's JSON Output Is Noise. I Wrote a Formatter with a Baseline Diff.
sendotltd profile

PHPStan's JSON Output Is Noise. I Wrote a Formatter with a Baseline Diff.

#php #phpstan #cli #tutorial
Comments
9 min read
I Got Tired of Pasting EXPLAIN Plans Into Web Tools, So I Wrote pg-explain-viz
sendotltd profile

I Got Tired of Pasting EXPLAIN Plans Into Web Tools, So I Wrote pg-explain-viz

#rust #postgres #cli #tutorial
Comments
10 min read
Discord Slash Commands Without an SDK: ed25519 in 250 Lines of TypeScript
sendotltd profile

Discord Slash Commands Without an SDK: ed25519 in 250 Lines of TypeScript

#typescript #hono #discord #tutorial
Comments
10 min read
Writing an HTTP Load Tester That Doesn't Lie About p99
sendotltd profile

Writing an HTTP Load Tester That Doesn't Lie About p99

#rust #benchmark #http #tutorial
Comments
8 min read
A Portfolio-Sized URL Shortener in 300 Lines of PHP
sendotltd profile

A Portfolio-Sized URL Shortener in 300 Lines of PHP

#php #slim #urlshortener #tutorial
1
Comments
9 min read
Describing Cron Expressions: Why Templates Don't Work, and What Does
sendotltd profile

Describing Cron Expressions: Why Templates Don't Work, and What Does

#typescript #cron #cli #tutorial
Comments
8 min read
Writing a YAML Linter in Rust Because YAML Is Secretly Terrible
sendotltd profile

Writing a YAML Linter in Rust Because YAML Is Secretly Terrible

#rust #yaml #cli #tutorial
Comments
11 min read
Parsing Prisma Schema By Hand: A 300-Line CLI That Emits Mermaid ER Diagrams
sendotltd profile

Parsing Prisma Schema By Hand: A 300-Line CLI That Emits Mermaid ER Diagrams

#typescript #prisma #mermaid #tutorial
Comments
10 min read
Debugging TCP by Building Your Own Logging Proxy in 400 Lines of Rust
sendotltd profile

Debugging TCP by Building Your Own Logging Proxy in 400 Lines of Rust

#rust #tokio #networking #tutorial
1
Comments
8 min read
Building an XPath Query Tool in PHP — Slice XML Like a Pro
sendotltd profile

Building an XPath Query Tool in PHP — Slice XML Like a Pro

#php #cli #xml #xpath
Comments
8 min read
Building a Changelog Generator in Rust — From Conventional Commits to Keep a Changelog
sendotltd profile

Building a Changelog Generator in Rust — From Conventional Commits to Keep a Changelog

#rust #cli #git #changelog
Comments
8 min read
Building a .gitignore Generator CLI in Python — 51 Templates, Zero Dependencies
sendotltd profile

Building a .gitignore Generator CLI in Python — 51 Templates, Zero Dependencies

#python #cli #git #devtools
Comments
9 min read
Building a MIME Type Lookup CLI in TypeScript — 800+ Types, Magic Bytes, and Zero Dependencies
sendotltd profile

Building a MIME Type Lookup CLI in TypeScript — 800+ Types, Magic Bytes, and Zero Dependencies

#typescript #cli #mime #fileformat
Comments
8 min read
Building a TOML Formatter in Rust — Sorted Keys, Aligned Equals, and CI-Friendly Check Mode
sendotltd profile

Building a TOML Formatter in Rust — Sorted Keys, Aligned Equals, and CI-Friendly Check Mode

#rust #cli #toml #formatter
Comments
8 min read
Building an HTTP Status Code Reference CLI in PHP — No Dependencies Required
sendotltd profile

Building an HTTP Status Code Reference CLI in PHP — No Dependencies Required

#php #cli #http #tutorial
Comments
8 min read
I Wrote a .env Linter from Scratch — Here Are the 9 Rules That Actually Matter
sendotltd profile

I Wrote a .env Linter from Scratch — Here Are the 9 Rules That Actually Matter

#python #cli #dotenv #tutorial
Comments
8 min read
Building a Configurable TCP Echo Server in Rust with Tokio
sendotltd profile

Building a Configurable TCP Echo Server in Rust with Tokio

#rust #networking #tcp #cli
Comments
8 min read
Implementing semver 2.0.0 from scratch in TypeScript — no semver package allowed
sendotltd profile

Implementing semver 2.0.0 from scratch in TypeScript — no semver package allowed

#typescript #cli #semver #devtools
Comments
9 min read
Building a strict INI parser from scratch in Python — no configparser allowed
sendotltd profile

Building a strict INI parser from scratch in Python — no configparser allowed

#python #cli #config #parser
Comments
8 min read
Building a Concurrent TCP Port Scanner in Rust with Tokio Semaphores
sendotltd profile

Building a Concurrent TCP Port Scanner in Rust with Tokio Semaphores

#rust #networking #async #cli
Comments
9 min read
phpcron: a tiny PHP CLI for poking at cron expressions
sendotltd profile

phpcron: a tiny PHP CLI for poking at cron expressions

#php #cli #cron #scheduling
Comments
8 min read
Writing a compliant RFC 6902 JSON Patch CLI in one evening, zero runtime deps
sendotltd profile

Writing a compliant RFC 6902 JSON Patch CLI in one evening, zero runtime deps

#typescript #cli #json #rfc6902
Comments
9 min read
A 600-line Rust log rotator, or: what logrotate would look like if it had no config file
sendotltd profile

A 600-line Rust log rotator, or: what logrotate would look like if it had no config file

#rust #cli #logs #ops
Comments
10 min read
Micro-benchmarking TypeScript Without Lying to Yourself
sendotltd profile

Micro-benchmarking TypeScript Without Lying to Yourself

#typescript #benchmark #cli #tutorial
1
Comments
8 min read
The Four Rate-Limiting Algorithms You Should Know (I Built a PHP Service That Runs All Five)
sendotltd profile

The Four Rate-Limiting Algorithms You Should Know (I Built a PHP Service That Runs All Five)

#php #slim #ratelimiting #tutorial
Comments
10 min read
A Polite Port Scanner in 400 Lines of Tokio
sendotltd profile

A Polite Port Scanner in 400 Lines of Tokio

#rust #cli #networking #tutorial
Comments
9 min read
Counting TypeScript Escape Hatches — A Zero-Dependency CLI with a Baseline Gate
sendotltd profile

Counting TypeScript Escape Hatches — A Zero-Dependency CLI with a Baseline Gate

#typescript #cli #migration #tutorial
Comments
9 min read
The similar crate is underrated: I wrote a colored diff CLI in a weekend
sendotltd profile

The similar crate is underrated: I wrote a colored diff CLI in a weekend

#rust #cli #diff #tutorial
Comments
8 min read
A Minimum-Viable RSS Aggregator in TypeScript with Hono
sendotltd profile

A Minimum-Viable RSS Aggregator in TypeScript with Hono

#typescript #hono #rss #tutorial
Comments
12 min read
SQLite's PRAGMAs You Never Remember — I Put Them in a CLI
sendotltd profile

SQLite's PRAGMAs You Never Remember — I Put Them in a CLI

#rust #sqlite #cli #tutorial
1
Comments
8 min read
A Self-Hosted PHP Contact Form Backend Without CAPTCHA
sendotltd profile

A Self-Hosted PHP Contact Form Backend Without CAPTCHA

#php #slim #webform #tutorial
Comments
7 min read
I Built jq for TOML Because My Shell Scripts Deserved Better
sendotltd profile

I Built jq for TOML Because My Shell Scripts Deserved Better

#rust #cli #toml #tutorial
Comments
9 min read
loading...