Tutorials

Cross-check ISO-4217 currency codes against sovereign states — complement dialing-code lookups when validating invoices, fraud rules, and localization matrices.

Answer “how old am I on this visa deadline?” and plan milestone timelines — with locale-aware calendar math handled locally.

Compare savings accounts, crypto yield programs, and promotional CDs using consistent annualized numbers — compounding frequency included.

Quick screening math using height and mass — helpful for orientation, not diagnosis; combine with clinical guidance for real decisions.

Diagnose why newsletters bounce, spoofing scores fail, or Gmail tabs reject transactional mail — all lookups stay in your browser session.

Resize outputs for CDN budgets, pick lossy vs lossless trade-offs, and preview quality sliders — without uploading originals to a sketchy converter site.

Turn README drafts, changelog notes, and knowledge-base stubs into clean HTML fragments — ideal for CMS paste workflows without spinning up a local build.

Annual, monthly, or weekly pay → hourly equivalents with adjustable workweek assumptions — useful before signing employment agreements or consulting SOWs.

Rasterize icons and illustrations for slide decks, legacy CMS fields, and email clients that still choke on vector MIME types.

Batch-transform labels, enum keys, and prose casing without touching your editor — useful when refactoring APIs, cleaning spreadsheets, or matching a style guide.

Swap metric ↔ imperial instantly when reading datasheets, recipes, or fitness trackers — handy for travel, engineering reviews, and classroom demos.

Measure copy length against editorial limits, localization budgets, and SEO snippets — with instant stats for Asian scripts and whitespace-aware token counts.

Bundle multi-resolution icons for classic desktop browsers and Windows shortcuts — without wrestling with legacy ImageMagick recipes.

Square social posts, 16:9 hero bands, and passport-style crops — processed locally so portrait shoots and UI captures never hit a third-party server.

Storyboards, scanned receipts, and design review packets — combine ordered pages without emailing gigabytes of loose PNGs.

Turn formal invoice captions like 叁万肆仟伍佰陆拾柒元整 into digits auditors can spreadsheet — ideal for finance ops handling scanned vouchers.

Hide complex WPA2 passwords behind a printable QR — ideal for cafés, Airbnb binders, and conference registration desks.

Text or logo overlays with adjustable opacity and tiling — keep social previews and beta captures traceable without Photoshop batch jobs.

Diagonal CONFIDENTIAL banners, light-repeat tiling, and subtle opacity tweaks — useful before Slack-ing screenshots or exporting PDF previews.

A scenario-driven guide to spotting line, word, and structural changes between two blocks of text or code, without ever uploading them to a server.

Beautify and minify JSON, JavaScript, HTML, CSS, and SQL with one click — entirely in the browser, with sensible defaults that match the conventions your linter expects.

Convert text between Simplified and Traditional Chinese with regional variants for Mainland, Hong Kong, and Taiwan, plus tips for catching the proper-noun edge cases an automatic converter cannot.

Build URL, vCard, Wi-Fi, and plain-text QR codes with custom colors and error-correction levels — generated locally in the browser, exported as PNG or SVG.

Stop breaking pages and APIs with stray quotes, ampersands, and Unicode. Convert text to and from safe escaped forms for HTML, URL, JavaScript, JSON, CSV, and XML.

Why epoch time matters, the second-vs-millisecond gotcha that keeps biting engineers, and how to convert any timestamp to a readable date in any time zone.

Confirm bank holidays, regional observances, and school-closure days in any country before you schedule meetings, run paid ads, or page your global on-call rotation.

Find the smallest overlapping working window across two, three, or four locations using a visual slider — without a single subtraction or DST landmine.

Build a personalized world clock for the cities you actually care about, watch DST handovers, and stop doing time-zone math in your head before standups.

When and why to use Base64, Base64-URL, Base32, and hex; what to do when binary cannot be treated as ASCII; and how to decode without losing trailing nulls.

Pick the right hash algorithm for the job, verify file integrity in one click, and understand why MD5 is fine for cache keys but a security disaster for passwords.

Sign API requests with a shared secret, debug webhook payloads, and verify Stripe / GitHub / AWS-style signatures with the right HMAC algorithm and digest format.

Verify HMAC, RSA, and ECDSA signatures over an arbitrary payload using a public key or shared secret — useful for API integrations, JWTs, and webhook debugging.

See how money grows when interest itself earns interest, compare compounding frequencies, and answer the actual question — should I invest the lump sum now or month by month?

The bank quotes 5%, but with origination fees and front-loaded interest, you actually pay 6.4%. Learn how to compute the real APR / IRR and compare loan offers honestly.

Estimate monthly payments, build the amortization schedule, and compare equal-payment vs equal-principal repayment plans before signing a 30-year commitment.

Quantify exactly how much interest a one-time bonus payment or a recurring $200 extra saves you, and see whether shortening the term beats lowering the monthly payment.

Generate the formal big-character (大写) Chinese amount required on invoices, contracts, and bank documents — including the trailing 整 / 角 / 分 conventions.

Look up geo-IP, ASN, ISP ownership, and reverse DNS records for any IPv4 or IPv6 address — useful for security triage, traffic analysis, and validating CDN routing.

Decompose any URL into protocol, host, path, and query parameters; tweak individual values for API testing; and decode percent-encoded characters in one step.

Capture User-Agent, screen, viewport, OS, and feature flags for bug reports and compatibility testing — without installing a single extension.

Shrink JPEG, PNG, and WebP files for the web with quality presets that match your use case — featured images, product photos, thumbnails, or email attachments.

Inspect GPS coordinates, camera settings, and timestamps embedded in JPEG/HEIC files, and strip the bits you don't want to share before publishing online.

Decode `data:image/...` URIs from API responses, browser snapshots, or copy-pasted snippets back into a PNG or JPEG you can save and share.

Translate any color between HEX, RGB, HSL, and OKLCH; build accessible contrast pairs; and export a palette your design system can rely on.

Embed small icons and watermarks directly in HTML, CSS, JSON, or email templates as Base64 — no extra HTTP request, no missing assets.

Stop guessing what 401 vs 403 means: a developer-focused tour of every status family with realistic examples, anti-patterns, and the codes that actually matter for SEO.

Files, processes, networking, and text manipulation — the Linux commands you reach for in production triage, with the flag combos that separate intermediate from expert.

From cloning to rebasing to recovering after a force-push disaster — the Git commands you actually use, with copy-pasteable invocations and one-line explanations.

Cross-reference ISO-3166 alpha-2/alpha-3, numeric codes, calling codes, currencies, capitals, and TLDs for any country — without bouncing between Wikipedia tabs.

What the People's Bank of China LPR is, why your floating-rate mortgage moves with it, and how to read the 1-year and 5-year+ history charts to plan future payments.