ZeroUtil Blog
Long-form guides on the tools we build and the problems they solve. Every article stays focused on what runs in your browser — no cloud uploads, no accounts, no dark patterns.
Featured guides
The Developer's JSON Guide: Everything Worth Knowing About JSON in 2026
A comprehensive guide to JSON — the spec, the variants, the tooling, debugging, JWT and Base64 context, and how to ship systems that don't break on malformed payloads.
The Online Privacy Guide: Practical Threat Models for Browser-Based Work in 2026
A comprehensive guide to online privacy in 2026 — threat models, browser-based vs. cloud tools, passwords, encryption, and the habits that matter most.
All articles
AES-GCM vs AES-CBC: Which Mode to Use and Why
What block cipher modes do, why GCM has mostly replaced CBC for new code, the IV and authentication rules that matter, and where each mode still earns its place.
Flesch-Kincaid Explained: What the Score Means and How to Use It
How the Flesch Reading Ease and Flesch-Kincaid Grade Level scores are computed, what they're good for, and the limits worth knowing before you optimize for them.
How to Calculate a Sale Discount: Formulas, Examples, and Common Traps
The math behind percent off, stacked discounts, sales tax order, and the tricks retailers use to make a discount look bigger than it is.
The 90-Minute Sleep Cycle Rule: What It Actually Means
How sleep cycles really work, why the 90-minute rule is a useful approximation, and how to time bedtime so you wake up between cycles instead of mid-cycle.
How US Federal Tax Brackets Work (2024 Guide)
Marginal vs effective tax rates, how the brackets stack, what your 'tax bracket' actually means, and the worked example most people get wrong.
How QR Codes Actually Work: A Practical Guide
What the squares mean, how error correction works, when to use which encoding mode, and why your printed QR code sometimes doesn't scan.
Unix Timestamps and Timezones: The Confusion That Eats Your Week
A practical walkthrough of Unix time, timezones, daylight saving time, and the handful of patterns that keep teams from shipping date bugs to production.
Compound Interest, Explained Like You Actually Have to Use It
The math behind compound interest, why the Rule of 72 works, and why time matters more than rate for most real financial decisions.
Password Strength in 2026: What Length and Character Sets Actually Buy You
A practical look at entropy, NIST's current guidance, real GPU cracking speeds in 2026, and why passphrases beat forced complexity every time.
Never Paste This Into a Random Online Tool
A practical threat model for developers and knowledge workers who use web tools at work. What's actually safe, what isn't, and what to do instead.
Base64 Explained: What It Is, Why It Exists, and When Not to Use It
A practical walkthrough of Base64 encoding — what it actually does to your bytes, why it's not encryption, and the handful of real places it still earns its keep in 2026.
JWT Authentication Mistakes That Keep Appearing in Production
A tour of the JWT pitfalls that still ship to production in 2026 — algorithm confusion, weak secrets, missing expiry, and the subtle ways a library can fail open.
Why Your PDF Tool Should Run in the Browser, Not the Cloud
What actually leaks when you upload a PDF to a random online tool, what modern in-browser PDF libraries can genuinely do, and a checklist for before you upload anything sensitive.
Debugging Malformed JSON: A Field Guide
Every JSON parse error has a real cause hiding behind an unhelpful message. A practical guide to the five failure modes that produce 90% of the pain.
Client-Side Image Compression: What's Actually Happening in the Browser
How browsers compress images without touching a server — the real pipeline behind Canvas, OffscreenCanvas, and WebCodecs, and when it's not enough.
JSON vs. JSON5 vs. JSONC: Which One and When
Three formats that look nearly identical, behave completely differently, and produce a steady stream of parser errors when confused. A practical guide to telling them apart.
Percentages: The Five Mistakes That Trip Up Even Careful People
Percentage points vs. percent, symmetric vs. asymmetric changes, markup vs. margin, and the other places where percentage math quietly lies.
Character Limits on Social Platforms in 2026: What Actually Gets Counted
Current character limits for X, Bluesky, LinkedIn, Instagram, Threads, Mastodon, and TikTok — and how each counts emoji, URLs, and multibyte characters differently.
What Counts as a Word: Why Your Word Counter and Mine Disagree
Word counts vary by tool because 'word' isn't a well-defined unit. A practical look at whitespace splitting, Unicode, hyphens, emoji, and the counting edge cases.