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We share insights gained on the software development front line, including web development, algorithms, and performance optimization.
QR & Codes 10 posts
How to Check a QR Code's Error Correction Level
Read L, M, Q or H off a QR code from just two modules. The structure of the 15-bit format information, cross-checking with the second copy, and confirming it with an analyzer.
Read more →What the Corner Squares of a QR Code Do
Why there are three finder patterns and what the 1:1:3:1:1 ratio does, what timing and alignment patterns are for, and what fails when each is damaged.
Read more →Which Parts of a QR Code Can Be Lost and Still Recovered
Why the same missing area can succeed or fail depending on location and spread: per-codeword correction, the zigzag placement, block splitting and interleaving.
Read more →Why Coloured QR Codes Stop Scanning - Polarity and Contrast
A camera measures brightness, not hue. Inverted polarity, pairs such as red on black that carry no luminance difference, and how to lay a plain patch when the code sits over a photograph.
Read more →Static vs Dynamic QR Codes - Which One Can Be Repointed Later
A QR code cannot be edited. What a dynamic code actually does, why the redirect dependency gets heavier on printed material, and how URL length feeds back into print size.
Read more →QR Code Print Size - Working Backwards from Module Count
The four-module quiet zone, the 0.4 mm module guideline, and when the one-tenth-of-distance rule applies, with the steps for working the required millimetres back from the module count.
Read more →How to Identify a QR Code's Version from Its Module Count
The relation to modules per side, counting with the timing pattern, estimating from alignment patterns, and reading the version information present from version 7 up.
Read more →QR Code Specifications Explained (with sample QR codes)
From versions (1–40) and module counts, data capacity, and the four encoding modes to error correction, structure, and masking. We explain the specification while looking at actual generated sample QR codes. Includes a link to the generator tool.
Read more →Understanding QR Code Error Correction Levels — Why They Still Scan When Dirty
We explain, in clear terms, how QR codes remain readable even when partly hidden by a logo or smudged, from the perspective of error correction levels (L/M/Q/H) and Reed-Solomon codes.
Read more →QR Code Mask Patterns: The 8 Patterns and How One Is Chosen
Why the same string can look different: the eight condition formulas, penalty-based selection, and how readers reverse the mask.
Read more →Choosing Japanese Dummy Text
lorem ipsum cannot validate a Japanese layout. What differs, and which dummy text to use for each purpose.
Read more →Why a QR Code Won't Scan — Causes and Fixes
Contrast, quiet zone, resolution, error correction and data volume — the main reasons a QR won't scan and how to fix them, plus creator tips.
Read more →Barcode Specifications Explained (with sample barcodes)
We explain the characteristics and structure of EAN-13/JAN, EAN-8, UPC, CODE39, CODE128, ITF, and Codabar, along with how check digits work, using actual generated samples. Includes a link to the generator tool.
Read more →How to Restore an Unreadable QR Code from a Photo
Why Reed-Solomon error correction can read damaged QR codes, what enhancement, binarization, and unsharp masking actually do, how to tune each parameter, and the honest limits of recovery. With a link to the free restore tool.
Read more →What Is a Micro QR Code — Differences From Standard QR and When to Use It
Micro QR starts at 11x11 modules and has only one finder pattern. Here is what that costs you: the M1-M4 capacity limits, the error correction levels you cannot use, and the reader-support caveat to check first.
Read more →Claude Code 11 posts
Building Test Scenarios with Claude Code
The verification loop, RED-GREEN-REFACTOR in TDD, E2E verification via browser automation, and cross-verification with sub-agents. We explain how to build a test strategy based on research from external blogs.
Read more →How Django Co-creator Simon Willison Uses Claude Code
The idea of "designing the agent loop," YOLO mode and sandboxes, throwaway $5 Fly.io orgs, and using tests as a means of verification—explained with quotes.
Read more →How Top Engineers Use Claude Code
We look at how leading engineers around the world—Armin Ronacher, Simon Willison, Mitchell Hashimoto, and Boris Cherny—actually use Claude Code, drawing on their original posts.
Read more →Running Projects with Claude Code
The Explore → Plan → Code → Commit loop, spec.md/plan.md, CLAUDE.md, git worktree, and TDD. We organize a repeatable workflow based on official docs and practitioners' blogs.
Read more →How Ghostty's Creator Mitchell Hashimoto Uses AI Agents
Delegating research, harness engineering (AGENTS.md), real examples and costs in Ghostty, and the cautionary idea of "agent psychosis"—explained with quotes from his own blog.
Read more →Claude Code Subagents: Designing Delegation That Protects Your Context
Where files live (.claude/agents/), the name, description, tools, and model frontmatter, the isolated context window, and automatic delegation, explained with concrete examples based on the official docs.
Read more →Team Collaboration with Claude Code
Sharing CLAUDE.md, committing the .claude/ directory, GitHub Actions integration, MCP servers (Slack/Linear), and onboarding. We introduce how to build the foundations for team collaboration.
Read more →How Flask's Creator Armin Ronacher Uses Claude Code
claude-yolo with Docker, keeping logs in files, designing agent-friendly code, and CLI over MCP. We dig into the Flask creator's practices with quotes from the original article.
Read more →How Claude Code's Creator Boris Cherny Uses It
Running multiple Claudes in parallel, recording mistakes in CLAUDE.md, /commit-push-pr, moving from plan mode to auto mode, and "2–3x quality through verification"—with sources.
Read more →Documentation Management with Claude Code
CLAUDE.md and automatic memory, initialization with /init, generating JSDoc/OpenAPI from code, and keeping docs in sync with hooks and CI. We explain how to keep documentation from going stale.
Read more →Claude Code Hooks: Automating Your Workflow
Configuring hooks in settings.json, events like PreToolUse, PostToolUse, and Stop, the matcher, blocking with exit code 2, and JSON I/O, based on the official docs.
Read more →Fundamentals & Algorithms 7 posts
HEIC/HEIF Licensing and Patents, Explained
Container (HEIF) versus codec (HEVC), the license terms of libheif, libde265 and x265, why software licensing and patent licensing are separate problems, and the current state of the HEVC patent pools. With sources and a link to the converter tool.
Read more →Converting Between Wareki (Japanese Era) and Gregorian Years
Start dates for Reiwa, Heisei and Showa, simple formulas like "Gregorian - 2018 = Reiwa", and why two eras can share one year. Includes a link to the converter tool.
Read more →How Diff Works — Finding Changes with Longest Common Subsequence
How diff finds changes between two texts, explained through the Longest Common Subsequence and dynamic programming with worked examples.
Read more →Intro to Sorting Algorithms — 7 Methods Chosen by Complexity
From bubble sort to quicksort and merge sort. We organize how the major sorting algorithms work and their time complexity (Big O notation), and explain how to choose the right one for the job.
Read more →Core Web Vitals: A Practical Guide — Improving Speed and Perceived Performance
Centered on the three metrics LCP, INP, and CLS, we summarize concrete measures to improve website load speed and user experience—from measurement to implementation, with a practical focus.
Read more →Camera RAW Formats and Their Licenses
LibRaw's LGPL 2.1 / CDDL 1.0 choice, dcraw's RESTRICTED clause, Adobe DNG's patent license and ISO 12234-4, and the constraints on each vendor's camera SDK. With sources and a link to the extractor tool.
Read more →Binary and Hexadecimal Explained — How Computers Represent Numbers
How binary and hexadecimal work, why computers use them, and how to convert to and from decimal, with a 0-15 table and examples.
Read more →Data & Conversion 13 posts
Time Zones vs UTC Offsets - Why +09:00 Is Not Enough
Asia/Tokyo and +09:00 are not the same thing. What breaks with daylight saving time and historical dates, why future appointments must not be stored as UTC, and what to store instead.
Read more →CRLF vs LF - What Line Endings Actually Break
The difference between CRLF and LF and the concrete failures they cause: bad interpreter, Git diffs covering every line, and stray carriage returns in config values. Includes .gitattributes.
Read more →Characters to Words - A Practical Conversion Guide
Estimate word count in English with "characters incl. spaces / about 6", why word count is ambiguous in Japanese, and how to count for real. Includes a link to the character counter.
Read more →What Is a Check Digit - EAN-13, ISBN, and Luhn
How a single trailing digit catches typing errors, with the calculation steps for EAN-13/JAN, ISBN-13 and credit cards (Luhn). Includes hand calculation and JavaScript examples, plus a link to the calculator.
Read more →Counting Characters and UTF-8 — Characters, Bytes, and Graphemes
Why a "character count" changes with how you count — explained through Unicode code points, UTF-8 byte length, JS string length (UTF-16), and grapheme clusters, with worked examples for emoji and combining characters. Includes a link to the counter tool.
Read more →What Is a UUID? How v4 Works, Collision Probability, and When to Use It
The notation of the 128-bit UUID and its versions (v1/v4/v5/v7), the random structure of v4, collision probability from the birthday problem, and where to use it in distributed systems — explained in line with the RFCs. Includes a link to the generator tool.
Read more →What Is YAML - Differences from JSON and Basic Syntax
How YAML differs from JSON, the basic syntax (indentation, lists, maps, multi-line strings, anchors), and where it is used, with example code. Covers pitfalls such as the tab ban and the Norway problem, plus a link to the converter.
Read more →What Is URL Encoding? Percent-Encoding Explained
Reserved vs. unreserved characters, how percent-encoding works (UTF-8 byte by byte), and the difference between encodeURI and encodeURIComponent.
Read more →What Is Unix Time? Epoch Seconds, Time Zones, and Year 2038
What epoch seconds are, seconds vs. milliseconds, time zones and UTC, leap seconds, and the Year 2038 problem.
Read more →What Is JSON? Syntax, Data Types, Common Errors, and Formatting Tips
JSON's six data types and syntax rules, common errors such as trailing commas and single quotes, when to pretty-print vs. minify, and how validation works — explained in line with RFC 8259. Includes a link to the formatter/validator tool.
Read more →What Is Base64? How It Works, Use Cases, UTF-8 and URL-Safe Encoding
How three bytes map to four characters and padding, use cases like email and Data URLs, handling Japanese and emoji via UTF-8, and URL-safe Base64 (RFC 4648 §5). We also make clear it is not encryption, with a link to the converter tool.
Read more →What Is a Code Point - Unicode, UTF-8, and UTF-16
What a value like U+3042 means, how UTF-8 encodes it in 1 to 4 bytes, and why emoji become surrogate pairs. With JavaScript you can run yourself and a link to the inspector tool.
Read more →CSV vs JSON — Differences and How to Convert Between Them
The differences between CSV and JSON (nesting, types, size, use cases) and key points for converting between them, with a comparison table.
Read more →UUID v7 and Time-Ordered Keys: Benefits and Pitfalls as a Primary Key
UUID v7 sorts roughly by creation time thanks to its leading 48-bit millisecond timestamp. Covers index fragmentation from random v4 primary keys, what v7 actually fixes, and the pitfalls: readable timestamps and ordering that is not guaranteed within a millisecond.
Read more →Never Use Real Values in Test Data - Names, Addresses, and Phone Numbers
Real values in fixtures send real notifications to real people. Covers the reserved ranges from RFC 2606 and RFC 5737, safe ways to build names and addresses, and why cloning production data is the wrong shortcut.
Read more →How to Make Up Dummy Company Names — Why to Avoid Real Trade Names
Putting a real company name in your test data means that screenshot ships with a real business attached to it. Why to avoid real trade names, and how to build fictional ones from a stem, an industry word and a legal entity type.
Read more →Security 7 posts
CVE-2026-54763 in Traefik: When a Stripped Header Still Reaches the Backend
Only the hyphenated spelling was stripped, so the underscore variant reached the backend. Affected and fixed versions, both CVSS scores, and why upgrading alone is not enough.
Read more →AWS Security Testing: What Needs Prior Approval and What Does Not
AWS's official penetration testing policy as checked on 4 August 2026: the permitted services, the prohibited activities, and what needs a Simulated Events form in advance.
Read more →CVE-2018-1270 in Spring Framework: Affected Versions and How to Check
Reconciling NVD with the vendor advisory: why the 4.3.x fix is 4.3.16 and not 4.3.15, the CVSS scores, how to tell whether you are affected, and its absence from CISA KEV.
Read more →Checking Cisco NX-OS Advisories for Your Release
How to find which advisories apply to a release such as 9.3(13): reading show version per platform, using the Cisco Software Checker, and its two key limitations.
Read more →What Is a JWT? Structure, Signatures, and Use Cases
The three parts of a JWT, registered claims, HMAC and public-key signatures, why the payload is not encrypted, and security pitfalls.
Read more →What Is a Hash Function? SHA-256, Use Cases, and Why It's Not Encryption
The one-way nature of hash functions, how they differ from encryption, SHA-256 use cases, and how to store passwords correctly (salting/stretching).
Read more →HTML Escaping and XSS — Why You Must Encode Special Characters
Why HTML escaping matters, how cross-site scripting (XSS) works and its types, and context-aware output defenses.
Read more →Web & Coding 5 posts
What Is Lorem Ipsum? Origin, How to Use It, and a Free Generator
The origin (Cicero) and history of the meaningless placeholder text 'Lorem ipsum', why it is used in design, cautions for Japanese, and how to use the free generator (paragraphs / sentences / words).
Read more →Naming Conventions and Case Styles — camelCase, snake_case, kebab-case, PascalCase
The differences between camelCase, snake_case, kebab-case and PascalCase, language conventions, and how to stay consistent.
Read more →Color Codes Explained — HEX vs RGB vs HSL and How to Convert
The differences between HEX, RGB and HSL for color on the web, with step-by-step conversion algorithms and worked examples — 3-digit HEX and alpha, why HSL is intuitive, and contrast basics. Includes a link to the converter tool.
Read more →Text Processing Tips — Master Dedupe, Sort, and Trim
Tips for everyday text wrangling — sorting (lexicographic vs. numeric), removing duplicates, trimming blanks — alongside command-line equivalents.
Read more →Regular Expressions for Beginners — Common Patterns and Syntax
The building blocks of regular expressions — character classes, quantifiers, groups, anchors and flags — with practical examples for email, URLs and dates.
Read more →Networking 5 posts
HTTP 200 Does Not Mean the URL Is Correct
A wrong username segment can be absorbed by a 301, so a link checker sees 200. Measured on 4 August 2026: comparing final URLs and verifying ownership via a public API.
Read more →Tracking Sites That Publish No Feed
A 404 on a guessed feed URL can be 170 KB of HTML. Measured results, the three signals that decide whether a fetch succeeded, and splitting zero items into three states.
Read more →HTTP Status Codes Explained — What 200/301/404/500 Mean
The three-digit status codes a web server returns, explained from scratch across the five 1xx–5xx classes. Covers the differences between 301 and 302, 401 and 403, 404 and 410, redirects and SEO, the 304 cache response, and rate-limiting 429. Includes a link to the lookup tool.
Read more →Subnetting and CIDR Basics — Understand IP Address Division from Scratch
From the 32-bit structure of IPv4 to subnet masks and prefix lengths (CIDR like /24), network and broadcast addresses, usable host counts, private addresses and IP classes, and worked subnetting examples — explained from the ground up. Includes a link to the calculator tool.
Read more →What Is an API? How Web Services Connect (REST, Endpoints, Auth)
Endpoints and HTTP methods, what requests and responses contain, the ideas behind REST, authentication with keys and tokens, and the CORS and rate-limit pitfalls.
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