ssh-keygen -t ed25519: Which SSH Key Type to Use
Why ssh-keygen -t ed25519 is the right default, how Ed25519, ECDSA and RSA compare, what quantum computing really changes, and using one key for Git and SFTP.
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Practical writing on the things these tools touch: SSH keys, UUIDs, JWTs, tokenization, image formats and the maths behind them. No fluff, worked examples. Subscribe via RSS →
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How Random Is a UUID? Entropy, v4, and v7
A v4 UUID carries 122 bits of randomness; a v7 carries 74. How each is built, where each is used, and why randomness and entropy are not the same thing.
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How to Choose a Web Framework (Without Reading 50 Listicles)
A decision framework for picking a web framework: the four questions that actually narrow the field, and why team familiarity beats benchmarks.
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How to Write an Invoice: What to Include (and What Gets You Paid)
The nine things every invoice needs, how to number invoices properly, what Net 30 means, and the wording changes that measurably speed up payment.
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What Is a HEIC File? (and How to Convert iPhone Photos to JPG)
HEIC is the iPhone's default photo format — half the size of JPEG at the same quality, but it won't open everywhere. Why Apple uses it, and how to get JPGs.
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Are Online PDF Tools Safe? What Happens When You Upload a File
When you upload a PDF to a free online tool, where does it actually go and how long does it live there? The real risks, and the browser-only alternative.
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Cron Syntax Explained: A Cheatsheet of the Schedules Everyone Actually Uses
The five cron fields, the schedules everyone actually needs — every 5 minutes, daily at midnight, weekdays at 9 — and the day-of-week trap.
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How to Format SQL: A Pragmatic Style Guide
Keyword casing, leading vs. trailing commas, indentation that shows query structure, and JOIN/CTE layout — the SQL rules that make queries reviewable.
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How to Unscramble Words: Techniques Top Scrabble Players Use
Anagram techniques that actually work: alphagrams, prefix/suffix chunking, and the letter math behind Scrabble, Wordle and newspaper jumbles.
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Average Reaction Time: Benchmarks by Age, Device, and Stimulus
The average human reaction time is about 250 ms to a visual stimulus. How that shifts with age, hardware and sound vs. sight — and how to test yours.
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SPF, DKIM, and DMARC Explained: Why Your Email Lands in Spam
What SPF, DKIM and DMARC actually check, how the three DNS records fit together, and the misconfigurations that send legitimate email to spam.
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Chunking Strategies for RAG: Why Chunk Size Makes or Breaks Retrieval
Most RAG retrieval failures start at chunking. Fixed-size vs. structure-aware vs. semantic chunking, sensible size and overlap defaults, and how to evaluate.
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What's Inside a QR Code? How They Encode Data (and the Risks)
A QR code is a 2D barcode holding text with heavy error correction. How the modules encode data, why a torn or logo'd code still scans, and the quishing risk.
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Common JSON Errors and How to Fix Them
"Unexpected token" tells you something broke, not what. The handful of mistakes behind almost every JSON parse error, with the one-line fix for each.
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WebP vs. JPEG vs. PNG: Which Image Format, and When
Picking the wrong image format bloats pages and hurts Core Web Vitals. Lossy vs lossless, transparency, when WebP and AVIF win, and what compression saves.
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Hex, RGB, HSL: How CSS Color Formats Work
#7c3aed, rgb(124 58 237) and hsl(258 83% 58%) are one colour. What each CSS colour format encodes, why HSL is the tweakable one, and where oklch fits.
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What Are Embeddings? Cosine Similarity Explained for Developers
Embeddings turn text into vectors so machines can compare meaning. What an embedding is, why cosine similarity is the metric, and how semantic search works.
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How Much VRAM Do You Need to Run an LLM Locally?
Will that model fit on your GPU? Where VRAM goes (weights, the KV cache, overhead), what quantization actually saves, and a sizing table by GPU.
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How LLM Tokenization Works (and Why Your API Bill Is Higher Than You Think)
Tokens aren't words, and you're billed per token. How LLM tokenization works, why code and emoji cost more, and how to estimate your API bill before you ship.
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How to Read a TLS Certificate (and Spot a Bad One)
A TLS certificate is signed metadata binding a public key to a name. How to read the fields that matter — subject, SAN, issuer, validity — and spot red flags.
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Convert Your Valorant Sensitivity to CS2 (Without Losing Your Aim)
Moving from Valorant to CS2? Here's the exact sensitivity conversion, why cm/360 is what really matters, and how to keep the muscle memory you built.
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What Is a Good CPS? Average Click Speed and How to Click Faster
What counts as a good CPS (clicks per second)? See click-speed benchmarks by skill level, what affects your score, and proven ways to click faster.
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How TOTP and Authenticator Apps Actually Work
The 6-digit code isn't sent by the server. How TOTP works: a shared secret, an HMAC of the current time, and why the code rotates every 30 seconds.
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How to Share a Password Securely at Work (No Special Tools)
Slacking or emailing a password leaves it in logs forever. How to share one safely without a vault: the two-channel rule, and what never to do.
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HMAC vs. Hashing: How to Verify Webhooks and API Requests
A plain hash of a request body proves nothing. Why webhook verification needs HMAC (a keyed hash), how the flow works, and how to compare signatures safely.
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JWT Security: How JSON Web Tokens Work and How They Get Abused
A JWT isn't encrypted, only signed, so anyone can read the payload. How JWTs work, why alg:none is dangerous, and how to validate one safely.
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Debt Snowball vs. Avalanche: Which Pays Off Debt Faster?
Debt snowball vs. avalanche: the snowball builds momentum, the avalanche saves the most interest. See how each works, the trade-off, and which to pick.
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UUID v4 vs. v7: Which Should You Use for Database IDs?
UUIDv4 is random; UUIDv7 is time-ordered. Why random UUIDs fragment database indexes, how v7 fixes it, and a decision table for primary keys vs auto-increment.
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The UUID Versions Explained: What v1 to v8 (and Nil) Are For
UUIDs come in several versions, each for a different job. What v1, v3, v4, v5, v6, v7 and v8 (plus nil and max) are for, and which one to reach for.
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How Long Would It Take to Crack Your Password? The Real Math
Crack-time charts oversimplify. The real math of password strength: entropy in bits, guesses per second, why length beats complexity, and how to test yours.
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A Practical Regex Cheat Sheet: Patterns You'll Actually Use
A task-oriented regex cheat sheet: the building blocks that cover 90% of cases, greedy vs lazy, capture groups, copy-paste recipes, and the ReDoS pitfall.
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How Compound Interest Works (and Why Starting Early Wins)
Compound interest means earning interest on your interest. See the formula, a worked example, and why starting a decade earlier can beat saving far more later.
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Unix Timestamps Explained: Epoch Time, Time Zones, and the 2038 Problem
What a Unix timestamp really is: seconds since 1970 UTC. Seconds vs milliseconds, why you store UTC, the Year 2038 problem, and how to get epoch time anywhere.
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Base64 Isn't Encryption: What It Actually Does (and When to Use It)
Base64 is reversible encoding, not encryption: no key, no secrecy. How it works (3 bytes to 4 chars), why it exists, the 33% size cost, and what to use instead.
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SHA-256 Explained: What It Is and Why It's Everywhere
SHA-256 turns any data into a fixed 64-character fingerprint. A plain-English look at what a hash is, what SHA-256 is used for, and why you can't reverse it.
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Hello, Andergrove
Why Andergrove Software exists, and how this lean static site is built and maintained.
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IBM DataPower Gateway - Management APIs
A practical guide to the IBM DataPower Gateway REST management API: structure, key resources, and curl examples for reading and updating configuration.
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IBM DataPower Gateway - Docker for Local Development
How to run IBM DataPower Gateway locally as a free Docker service for development: setup, the docker run command explained, and enabling the Web UI.
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Introduction
Andergrove Software is a software services company from Canberra, Australia, run by Chris Hare — an introduction to the blog.
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