25free tools
6categories
0accounts or uploads
100%client-side
Small tools, properly made.
Tool Vio is a workbench of single-purpose online tools — generators, converters, " "checkers, calculators and counters. Every one of them runs entirely in your browser, so nothing " "you type, paste or open ever leaves your device.
Security
Passwords, hashes and IDs — lock things down properly.
SecurityPassword GeneratorRandom passwords, made on your device — never sent anywhere.
SecurityPassphrase GeneratorStrong passwords from random words — easy to remember, hard to guess.
SecurityUUID GeneratorFresh version-4 UUIDs in bulk — 1 to 50 at a time, ready to paste.
SecurityHash GeneratorFive hash fingerprints (MD5 to SHA-512) computed live as you type.
SecurityPassword Strength CheckerTest any password: entropy, crack time and weak-pattern warnings.
Images
Compress, resize, convert and favicon-ify without uploads.
ImagesImage CompressorShrink JPG, PNG and WebP photos — see the saving before you download.
ImagesImage ResizerResize any photo to exact pixel dimensions — right in your browser.
ImagesImage ConverterConvert between PNG, JPG and WebP — properly re-encoded, not renamed.
ImagesFavicon GeneratorFavicons from an image or a letter — all four sizes browsers ask for.
Colour
Pickers, palettes, gradients and contrast ratios.
ColourPalette GeneratorFive-colour palettes from one colour and a harmony rule.
ColourGradient GeneratorSmooth CSS gradients with live preview — copy production-ready code.
ColourContrast CheckerExact WCAG contrast ratios and pass/fail verdicts for any text colour.
ColourColour StudioOne colour in every format: HEX, RGB, HSL, HSV, tints and shades.
Data
JSON, Base64 and URL encoding — developer staples.
DataJSON FormatterPretty-print, minify and validate JSON with honest error messages.
DataJSON to CSV ConverterTurn JSON arrays into spreadsheet-ready CSV — and back again.
DataBase64 Encoder & DecoderEncode and decode Base64 with proper UTF-8 — emoji and accents intact.
DataURL Encoder & DecoderPercent-encode URLs or decode them back — live, as you type.
Text
Count, convert, compare and generate placeholder text.
TextDiff CheckerSee exactly what changed between two texts, line by line.
TextWord CounterLive word, character and sentence counts with read and speak times.
TextCase ConverterRestyle text in 13 cases — from UPPERCASE to camelCase — in one click.
TextLorem Ipsum GeneratorPlaceholder text by paragraph, sentence or exact word count.
Calculators
Everyday maths: BMI, age, units and percentages.
CalculatorsBMI CalculatorBody mass index with healthy-range guidance, metric or imperial.
CalculatorsAge CalculatorExact age from any birth date, plus totals and next birthday.
CalculatorsUnit ConverterLength, weight and temperature, converted live as you type.
CalculatorsPercentage CalculatorDiscounts, tips and change — every common percentage case.
Why another tools site?
Because most of them treat the tool as bait. The real product is usually the sign-up form, the file you upload, or the data trail you leave behind. Tool Vio is built the other way round: the tool is the product. You arrive, you do the job, you leave — and since every calculation happens inside your browser, there is no server quietly keeping a copy of what you made.
Built like a tool, not a funnel
Each page follows one template: the working tool at the top, then a plain-language explanation of what it does, its honest limits, and answers to the questions people actually ask. No countdown timers, no fake download buttons, no maze of ads between you and the result. If a tool cannot do something, the page says so.
Latest articles
ArticleWhat Makes a Password Strong in 2026Entropy, length vs complexity, passphrases, and password managers: what actually makes a password strong in 2026.
ArticleBMI: What It Measures, What It Misses, and How to Use ItHow BMI is calculated, what its categories mean, where it fails (athletes, age), and how to use it sensibly.
ArticlePercentages in Everyday Life: 7 Calculations Worth KnowingDiscounts, tips, interest, percentage change and reverse percentages: 7 percentage calculations with worked examples.
ArticleWhen Units Go Wrong: Real Disasters Caused by Conversion ErrorsThe Mars Climate Orbiter, the Gimli Glider, and other true stories of unit conversion errors, and how to avoid them.
ArticleHow Age Is Actually Calculated: Leap Years and Edge CasesLeap years, month lengths, and time zones: how age calculators really compute your age in years, months, and days.
Frequently asked questions
Are the tools really free?
Yes. Every tool on this site is free, with no account, no quota and no watermark on anything you download or copy.
Is anything I type or open uploaded?
No. All processing happens in your browser with JavaScript. There is no upload endpoint for the tools to send your data to — you can verify it by loading a tool, disconnecting from the internet, and watching it keep working.
Do the tools work offline?
Once a page has loaded, yes. The calculations are local, so a dropped connection does not stop the work.
Why does every tool live on its own page?
So each page can explain its tool properly and load fast, and so you can bookmark exactly the tool you use every week.
Can I suggest a new tool?
Yes — the contact page is the place. The collection grows by request, and gaps are listed honestly rather than filled with half-finished tools.