Small, precise tools for people who build on the web.
Free tools for CSS math, server config, data conversion, content formatting, and everyday tasks — 40 of them, built to be fast and to do exactly what they say, nothing more.
Fluid type, sized to fit.
font-size: clamp(1.25rem, 1.019rem + 2.22vw, 3rem);
All tools
40 free tools — search or filter by category.
CSS clamp() Calculator
Build a fluid clamp() value from a minimum and maximum size, with a live preview.
Runs entirely in your browser CSS & Design ToolsCSS Specificity Calculator
Compare two selectors and see exactly why one overrides the other.
Runs entirely in your browser CSS & Design ToolsFavicon Generator
Turn initials, text, or an emoji into favicons in every size you need, plus the HTML to install them.
Runs entirely in your browser Server & Deployment Tools.htaccess Redirect Generator
Build safe redirect and rewrite rules without guessing at Apache syntax.
Runs entirely in your browser Server & Deployment Tools.gitignore Generator
Combine clean .gitignore rules for multiple languages and tools at once.
Runs entirely in your browser Server & Deployment ToolsHTTP Header Checker
See a URL's response headers and which common security headers are missing.
Checked server-side — nothing is stored Data & Format ConvertersJSON ⇄ CSV Converter
Convert between JSON and CSV in either direction, with no file-size cap.
Runs entirely in your browser Data & Format ConvertersMarkdown ⇄ HTML Converter
Convert Markdown to clean HTML, or HTML back to Markdown.
Runs entirely in your browser Data & Format ConvertersUnix Timestamp Converter
Convert between Unix time and a readable date in any timezone.
Runs entirely in your browser Data & Format ConvertersCron Expression Generator
Build and get a plain-English explanation of standard and Quartz-style cron expressions.
Runs entirely in your browser Data & Format ConvertersJWT Decoder
Decode a JWT token in your browser — header, payload, and expiry, with optional HS256 signature verification.
Runs entirely in your browser Data & Format ConvertersBase64 Encoder/Decoder
Encode and decode Base64 with correct UTF-8 handling, a URL-safe variant, and file-to-data-URL conversion.
Runs entirely in your browser Data & Format ConvertersUUID Generator
Generate v4 and v7 UUIDs in bulk — with case and hyphen options, download, and a UUID inspector.
Runs entirely in your browser Data & Format ConvertersHash Generator
Compute MD5, SHA-1, SHA-256, and SHA-512 checksums of text or files, with hash compare and type detection.
Runs entirely in your browser Data & Format ConvertersURL Encoder/Decoder
Encode and decode URLs with correct UTF-8 handling, live conversion, and double-encoding warnings.
Runs entirely in your browser Data & Format ConvertersAI Token Estimator
Estimate LLM token counts for GPT and Claude-style models, with word/character stats and optional cost math.
Runs entirely in your browser Data & Format ConvertersRegex Tester
Test regular expressions with live match highlighting, flag toggles, capture-group inspection, and presets.
Runs entirely in your browser Data & Format ConvertersPassword Generator
Generate strong random passwords with crypto-grade randomness and an honest entropy readout.
Runs entirely in your browser Data & Format ConvertersColor Converter
Convert between HEX, RGB, HSL, and CMYK with a visual picker and a WCAG contrast checker.
Runs entirely in your browser Data & Format ConvertersLorem Ipsum Generator
Generate classic placeholder text by words, sentences, or paragraphs — plain, HTML, or Markdown.
Runs entirely in your browser Content Formatting ToolsOpen Graph & Twitter Card Generator
Preview and generate the meta tags that control how a link looks when shared.
Runs entirely in your browser Content Formatting ToolsPrompt Formatter
Clean up spacing, line breaks, and structure in a prompt before you send it. A formatting tool, not an AI evaluator.
Runs entirely in your browser Everyday ToolsTap Tempo BPM Counter & Metronome
Tap along to find any song's BPM, review your tap history, then practice with the built-in metronome.
Runs entirely in your browser Everyday ToolsOnline Tally Counter
Unlimited named tally counters with keyboard shortcuts, auto-save, per-counter reset, and CSV export.
Runs entirely in your browser Everyday ToolsCPS Test — Clicks Per Second
Measure your clicks per second over 1–60 seconds with a live speed chart, skill rating, and best-score history.
Runs entirely in your browser Everyday ToolsGamepad Tester — Controller & Joystick Test
Test every button, stick, and trigger live, spot stick drift, try vibration, and log inputs via the Gamepad API.
Runs entirely in your browser Everyday ToolsJapanese Name Generator (Kanji & Meanings)
Generate 115+ real Japanese names with kanji, romaji, and meanings — filter by gender and theme, plus a katakana converter.
Runs entirely in your browser Everyday ToolsGrade Calculator & GPA Calculator
Build wrong-answer grading charts with custom scales and plus/minus grades, plus a 4.0 GPA calculator with credit hours.
Runs entirely in your browser Everyday ToolsD&D 5e HP Calculator
Hit points for all 12 D&D 5e classes, levels 1–20, with CON modifier, Tough feat, Hill Dwarf, and multiclass support.
Runs entirely in your browser Everyday ToolsOnline Keyboard Tester — Test Every Key
Press any key to test it live: see key codes, spot stuck or dead keys, and check your whole keyboard in the browser.
Runs entirely in your browser Everyday ToolsPoint Buy Calculator
D&D 5e point buy: spend 27 points across the six abilities with the official cost table, live modifiers, and overspend protection.
Runs entirely in your browser Everyday ToolsGamepad Dead-Zone Calibrator
Tune per-stick dead zones and re-center drifting sticks, with a live raw-vs-corrected preview.
Runs entirely in your browser Everyday ToolsPercentage Calculator — X% of Y & More
Free percentage calculator: X% of Y, what percent X is of Y, percent increase/decrease and difference. Instant answers in your browser.
Runs entirely in your browser Everyday ToolsDays Calculator — Days Between Two Dates
Count days, weeks, months or years between two dates, add or subtract days from any date, and count business days only.
Runs entirely in your browser Content Formatting ToolsSora 2 Prompt Generator
Assemble structured AI video prompts — subject, action, camera angle, movement, lighting and style — with live preview and one-click copy.
Runs entirely in your browser Everyday ToolsSquare Face Generator
Roll random pixel-art faces, lock the parts you love, and download your avatar as a crisp PNG.
Runs entirely in your browser Everyday ToolsAge Calculator — How Old Am I Exactly?
Free age calculator: exact age in years, months and days from your date of birth, plus total days lived, weekday born and birthday countdown.
Runs entirely in your browser Content Formatting ToolsWord Counter
Count words, characters, sentences and paragraphs live — with reading time, speaking time and top keywords.
Runs entirely in your browser Content Formatting ToolsCharacter Counter — Chars, Words & More
Free character counter: characters with & without spaces, words, sentences, paragraphs and reading time — live as you type, in your browser.
Runs entirely in your browser Everyday ToolsPalworld Breeding Calculator
Find any Palworld breeding combo or reverse-search every parent pair for any Pal, on verified 1.0 data — special combos, formula and gender rules included.
Runs entirely in your browserBrowse by category
CSS & Design Tools
Small calculators for the CSS math you don't want to work out by hand.
Server & Deployment Tools
Generators and checks for the config files and headers behind your site.
Data & Format Converters
Convert between the formats developers actually move data through.
Content Formatting Tools
Shape text and metadata for how it will actually be shared or read.
Everyday Tools
Handy free online tools for music, gaming, study, names, and daily life.
From the blog
Plain-language guides on the concepts behind the tools.
Base64 Encoding Explained: How It Works & When to Use It
What base64 really does, why it inflates data by 33%, base64 vs base64url, and when to reach for it — and when not to.
Web DevelopmentRegex Cheat Sheet: Patterns, Flags & Examples
The regex syntax you actually use — character classes, quantifiers, groups, anchors, and flags — with copy-paste examples and honest caveats.
SecurityPassword Entropy Explained: Bits, Length & Real Security
What password entropy really measures, why length beats complexity, and how to read the bits number like a security engineer.
SecurityMD5 vs SHA-1 vs SHA-256 vs SHA-512: Which Hash Algorithm to Use
An honest comparison of common hash algorithms: what each is still good for, why MD5 and SHA-1 are broken for security, and what to use instead.
DevOpsCron Expressions Explained: Syntax, Examples & Pitfalls
Reading cron syntax field by field, the examples you’ll actually use, and the timezone/day-of-month traps that bite everyone once.
DesignCSS clamp() Explained: Truly Responsive Typography
How clamp() interpolates between minimum and maximum sizes, the math behind the preferred value, and fluid type without media queries.
DesignHEX vs RGB vs HSL: Color Formats Explained
When to use each CSS color format, why HSL wins for palettes, and what CMYK is actually for — with conversion examples.
AI & LLMsHow Many Tokens Is 1,000 Words? LLM Token Counts Explained
Tokens aren’t words: how tokenization works, the 4-characters-per-token rule of thumb, and what actually drives your API bill.
Web DevelopmentURL Encoding (Percent-Encoding) Explained
Why spaces become %20, when to encode (and what never to encode), plus the classic + vs %20 and double-encoding traps.
DevOpsHTTP Security Headers Explained
What Content-Security-Policy, HSTS, X-Frame-Options and friends actually do — and the minimal set every site should ship.
Web DevelopmentUUID v4 vs v7: Which Version Should You Use?
Random vs time-ordered UUIDs: how v7 fixes database index fragmentation, and when v4 is still the right call.
SecurityWhat Is a JWT? Structure, Claims & Security Explained
JSON Web Tokens explained: header, payload, and signature, what claims like exp and sub mean, and the security rules that actually matter.
Why Zento Tools Hub
Built for the actual task
Each tool does one job well instead of bundling in ten unrelated features.
Honest about how it works
Every tool page explains what happens to your data and how the result is calculated — no black boxes.
Fast on purpose
No unnecessary scripts or fonts. Tool-specific code only loads on the page that needs it.
Frequently asked questions
- Do I need an account to use these tools?
- No. Every tool on Zento Tools Hub works without signing up or logging in.
- Is my data sent to your server?
- Most tools run entirely in your browser and never send your input anywhere. A few, like the HTTP Header Checker, need to make a request on your behalf — those pages say so clearly and don't store what you enter.
- Do any of these tools use AI?
- No. Every tool here, including the Prompt Formatter, works through deterministic rules and calculations — not a language model. We'd rather be honest about that than dress up simple logic as "AI."
- Are the tools actually free?
- Yes. The site is supported by ads, not subscriptions or paywalls.