Free online tools that just work
52 calculators, converters and developer tools. Fast, private and free, with no sign-up. Everything runs in your browser.
Popular tools
See all 52 →Add Days to Date
Find the date that falls a given number of days, working days, weeks, months or years before or after any date.
Age Calculator
Enter a date of birth to get an exact age in years, months and days, plus the total in weeks and days and a countdown to the next birthday.
Base64 Encode & Decode
Convert text to Base64 and back, with full Unicode support and an option for the URL-safe alphabet used in JWTs and web addresses.
BMI Calculator
Work out your body mass index from your height and weight, see your category, and find the healthy weight range for your height.
BMR Calculator
Estimate how many calories your body burns at complete rest, using the three most widely used BMR formulas side by side.
Body Fat Calculator
Measure your neck, waist and (for women) hips to estimate body fat percentage, fat mass and lean mass.
Calorie Calculator
Estimate your daily calorie needs (TDEE) and get simple targets for keeping, losing or gaining weight.
Case Converter
Switch text between UPPERCASE, lowercase, Title Case, Sentence case and programmer formats like camelCase and snake_case.
Color Converter
Type or pick a color in any common format and get its HEX, RGB, HSL, HSV and CMYK values side by side.
Compound Interest Calculator
Work out how much a lump sum and regular monthly deposits will grow to, with any interest rate and compounding frequency.
CSV to JSON Converter
Paste CSV or spreadsheet data and get a JSON array of objects or arrays, with smart handling of quotes, numbers and empty cells.
Date Difference Calculator
Find how many days, weeks, months and weekdays are between any two dates, with an option to count the end date as well.
Browse by category
Developer Tools
Format, validate, encode and decode data without pasting it into a server. 10 tools
Text Tools
Count, clean, convert and rearrange text in a single click. 5 tools
Finance Calculators
Loans, savings, interest and investments, worked out in seconds. 10 tools
Health & Fitness Calculators
BMI, calories, body fat and other everyday health numbers. 6 tools
Math Calculators
Percentages, fractions, averages and the formulas you forgot from school. 2 tools
Unit Converters
Length, weight, temperature, data and more, with every common unit. 10 tools
Generators
Passwords, UUIDs, placeholder text and random numbers on demand. 4 tools
Image & Color Tools
Compress and resize images and convert colors, all on your device. 1 tools
Date & Time Tools
Ages, date differences, timestamps and time zones made simple. 4 tools
Why use ZTool?
Most online tools get in your way. They show pop-ups, ask for an email address, or quietly upload your files to a server you know nothing about. ZTool works differently. Every tool is a lightweight page that does its work on your own device, so your data stays with you and results appear as you type.
- Private by design. Your text, numbers and images are never sent anywhere. Disconnect from the internet after the page loads and most tools still work.
- Built for speed. Pages are pre-built static HTML with almost no JavaScript, so they open instantly even on slow mobile connections.
- Explained, not just calculated. Each tool comes with a plain-English guide that covers the formula, worked examples and common mistakes.
- Free for good. No accounts, no trials and no limits on how often you use a tool.