toolsy.one

Free online tools that respect your privacy

45+ developer, productivity, calculator and health tools that run entirely in your browser — plus plain-English guides on how they work. Nothing you type is ever uploaded.

Runs in your browser No uploads Free, no sign-up

Developer & Security

15 tools

Password generator

Strong passwords & memorable passphrases via WebCrypto.

JSON formatter

Format, validate and beautify JSON, with error messages.

Base64 encoder

Encode and decode Base64 text and URL-safe variants.

UUID generator

Generate bulk RFC 4122 v4 UUIDs using secure randomness.

Hash generator

SHA-1, SHA-256 and SHA-512 digests via the Web Crypto API.

SSL key generator

RSA / ECDSA key pairs in PEM, JWK and DER, in-browser.

Text diff checker

Compare two texts and highlight additions and deletions.

Regex tester

Test regular expressions live with capture-group breakdown.

URL encoder

Percent-encode / decode and parse query-string parameters.

HTML entity escaper

Escape and unescape HTML entities and special characters.

JSON ⇄ YAML

Convert data structures between JSON and YAML both ways.

SQL formatter

Capitalise keywords and indent SQL queries cleanly.

Epoch converter

Convert Unix timestamps to local & UTC dates and back.

Number base converter

Convert between decimal, hex, binary and octal.

JWT decoder

Decode a JSON Web Token header and payload locally.

Productivity

7 tools

Word counter

Count words, characters, sentences and reading time.

QR code generator

Turn links or text into downloadable QR codes.

Pomodoro timer

Focus timer using the Pomodoro technique.

Stopwatch & laps

A precise stopwatch with lap timing.

Markdown editor

Write Markdown with a live, sanitised HTML preview.

Case converter

Convert text between UPPER, lower, Title, camelCase and more.

Random number generator

Generate secure random numbers in any range, with options.

Calculators

10 tools

Candle wax calculator

Work out wax and fragrance amounts for candle making.

Unit converter

Convert length, weight, volume and temperature.

Loan & mortgage calc

Monthly payments, total interest and amortisation.

Percentage calculator

Work out percentages, percent change and "X is what % of Y".

Tip calculator

Calculate a tip and split the bill between any number of people.

Age calculator

Find an exact age in years, months and days from a date of birth.

Date duration calculator

Count the days, weeks and months between two dates.

Discount calculator

Find the sale price and amount saved for any discount.

Compound interest calculator

Project savings growth with compounding and regular contributions.

Scientific calculator

A calculator with powers, roots, logs and trig functions.

Health & Fitness

8 tools

BMI calculator

Body Mass Index in metric or imperial, with a cited formula.

Waist-to-height ratio

Calculate WHtR, an indicator of body-fat distribution.

Calorie & TDEE calculator

Estimate daily calories (BMR & TDEE) for your goals.

Body fat calculator

Estimate body-fat percentage with the US Navy method.

Ideal weight calculator

See healthy weight ranges from several standard formulas.

Water intake calculator

Estimate how much water to drink based on weight and activity.

One-rep max calculator

Estimate your 1RM and a full percentage lifting table.

Running pace calculator

Convert between pace, distance and time for any run.

Design

5 tools

Color tools

Convert HEX/RGB/HSL and build colour palettes.

Glassmorphism generator

Design translucent glass UI with live CSS export.

Contrast checker

Check colour contrast against WCAG AA and AAA.

Box shadow generator

Build layered CSS box-shadows with live sliders.

Lorem ipsum generator

Generate placeholder paragraphs, sentences or lists.

From our guides

See all guides →

Short, jargon-light explainers on the ideas behind the tools — how the maths works, what the formats mean, and how to use the results.

How to create a strong password (and why length beats symbols)

What actually makes a password hard to crack, why a long passphrase beats a short jumble of symbols, and how to manage credentials without losing your mind.

JSON vs YAML: which should you use, and when?

The real differences between JSON and YAML — readability, comments, data types and footguns — and a simple rule of thumb for choosing between them.

BMI explained: what it measures, and what it misses

Where the Body Mass Index formula comes from, how to read your number, and why it is a screening signal rather than a verdict on your health.

How to calculate percentages: the three types explained

The three percentage questions you actually run into — "X% of Y", "X is what % of Y", and percent change — with the formulas and worked examples.

Compound interest explained (with the formula)

Why compounding beats simple interest, how compounding frequency and regular contributions change the outcome, and the rule of 72.

How many calories should you eat? BMR vs TDEE

How your resting burn (BMR) and activity combine into daily calories (TDEE), and how a sensible deficit or surplus maps to weight change.

Built for speed and privacy

Every tool here runs locally in your browser — the text you paste, the numbers you enter and the passwords you generate never leave your device. No accounts, no uploads, no nonsense.

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