LazyTools — Free Online Tools That Never Upload Your Data

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The latest tools to land on LazyTools — freshly built and privacy-first like the rest.

Tool categories

Unit Converters Convert length, weight, temperature, volume and more — instantly.
Calculators Percentage, finance, health and everyday calculators.
Finance Compound interest, debt payoff, savings goal, ROI — exact, private, educational (not advice).
Mathematics Exact math: fractions with steps, primes, quadratics, statistics.
Biology & Lab DNA sequence tools, dilution, Punnett squares, Hardy–Weinberg, primer Tm — exact and private.
Statistics Normal distribution, binomial probability, confidence intervals, p-values — exact, with plain-English interpretation.
Chemistry & Lab Molar mass, chemical equation balancer, molarity, ideal gas, pH — exact, deterministic, with the working shown.
Physics SUVAT & projectile motion, Newton's laws, energy, gravitation, waves, Ohm's law, E=mc² — exact, with the working shown.
Size Converters Ring, shoe and bra sizes across US, UK, EU and more.
Home & DIY Paint, tile, concrete, mulch and wallpaper material estimators — metric or imperial.
Cooking & Kitchen Grams to cups, oven temperature, butter, recipe scaler and USDA meat temps — sourced and private.
Automotive Tire size, gear ratio, engine displacement, horsepower and fuel economy — exact, in your browser.
Fitness & Exercise Running pace, one-rep max, heart-rate zones, race predictor and calories burned — sourced formulas.
Pets & Animals Dog & cat age, feeding portions, gestation due dates, aquarium volume — vet-sourced formulas.
Gardening & Plants Plant spacing, raised-bed soil, fertilizer, watering, planting dates and compost — metric or imperial.
Music & Audio Note frequencies, BPM to delay time, tap tempo, metronome, intervals and transposing — for musicians.
Weather & Atmosphere Heat index, wind chill, dew point, wet-bulb and feels-like temperature — official NWS formulas.
Astronomy & Space Moon phase, sunrise & sunset, weight & age on other planets, light-time and telescope optics.
Photography Depth of field, field of view, crop factor, exposure, hyperfocal distance and print size.
Electronics & Circuits Resistor color & SMD codes, LED resistor, voltage divider, 555 timer, RC & LC filters, wire gauge, battery life.
Travel & Trips Flight distance & time, layover check, jet lag, tip-by-country, road-trip time, budget and luggage size.
3D Printing Filament weight/length & cost, print electricity, model scaling, E-steps & flow calibration, resin cost.
Solar & Energy Solar panel output, off-grid load, battery bank & inverter sizing, appliance cost, payback, voltage drop.
Homebrewing ABV, IBU, priming sugar, Brix↔gravity, hydrometer & refractometer correction, strike water, dilution.
Photo Size Maker Passport, visa & ID photos for 80+ countries — crop, check and export in your browser.
Developer Tools Formatters, encoders, hashes and other dev utilities.
File Converters CSV, JSON, XML, YAML and Markdown conversion.
Text Tools Counters, case converters, sorting and clean-up.
Generators QR codes, passwords, UUIDs and more.
Date & Time Timestamps, date math and timezone tools.
Calendars Convert between world calendars — Hijri, Hebrew, Persian, Julian and more.
Color Tools Color conversion, contrast and palettes.
Charts & Design Bar, line, pie and donut chart makers — from your data to PNG or SVG, in your browser.
Fonts & Typography Fancy text & font generators (bold, cursive, small caps) plus px-to-rem, type-scale and line-height tools.
Codes & Ciphers Morse code, NATO alphabet, binary and classic ciphers.
Productivity Pomodoro, planners, trackers and decision tools — saved locally.
Network & IT Subnet calculators, CIDR, chmod, cron and MAC tools.
Privacy & Security Metadata cleaners, encryption and password tools.
Image Tools Compress, convert and resize images locally.
PDF Tools Merge, split and rotate PDFs in your browser.
Audio & Video Trim, convert and adjust audio privately.

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Why "runs in your browser" matters

Most "free online tools" upload your files to their servers, process them there, and promise to delete them later. LazyTools is built differently: the processing code downloads to your device and runs there. There is no server to upload to — you can verify it yourself in your browser's network tab, or by switching off your internet connection mid-use.

See the technical details

One toolbox for the whole day

Convert anything. Length, weight, temperature, volume, data and hundreds more unit pairs with exact NIST/BIPM factors — plus ring, shoe and clothing sizes across US, UK and EU systems.

Do the math, exactly. Percentages, loans and mortgages, fractions with steps, primes, quadratics, statistics and BigInt-scale arithmetic that never silently rounds.

Run the lab. Balance chemical equations, compute molar mass, solve SUVAT and Ohm's law, and work through biology and statistics — each showing the working, not just an answer.

Handle everyday life. Plan finances, scale a recipe, size a tire, pace a run, tell your dog's age in human years, space a garden bed, tune an instrument or read the weather's "feels like."

Work with files, privately. Merge and split PDFs, compress and convert images, clean metadata, and make passport & visa photos for 80+ countries — all without an upload.

Build and inspect. Format and encode data, hash and check text, generate QR codes, passwords and UUIDs, and detect invisible characters or AI watermarks in text.

Frequently asked questions

Are LazyTools really free?

Yes — every tool is completely free, with no sign-up, no account, no trial, no usage limits and no paywalled features. There's nothing to install either; each tool opens instantly in your browser.

Do my files or data get uploaded to a server?

No. Every tool runs entirely in your browser using JavaScript and WebAssembly, so the files you open and the values you type are processed on your own device and never sent anywhere. You can prove it: switch off your internet connection mid-use and the tools keep working, or watch your browser's network tab — you'll see the page and an analytics tag load, but nothing carrying your files or inputs.

Does LazyTools track me or use cookies?

Only if you accept our cookie banner. We use Google Analytics to measure page visits, but it stays off by default (Google Consent Mode) — no cookies are set and no data is sent until you consent, and you can decline. Even when enabled, analytics only records that you visited a page; it never sees the files or values you enter into a tool, which stay on your device. We run no ads and never sell your data.

Do the tools work offline?

Yes. Because the processing happens in your browser, most tools keep working with no internet connection once the page has loaded — handy on a plane or with a patchy signal.

How many tools are there, and what kinds?

Over 960 tools across 41 categories — unit and size converters, everyday and financial calculators, exact math, chemistry, physics, biology and statistics, cooking, automotive, fitness, pet, gardening, music, weather, astronomy, photography and electronics calculators, travel and trip planners, 3D-printing, solar/off-grid energy and homebrewing calculators, developer utilities, text and color tools, generators, PDF and image tools, and a passport/visa photo maker.

How accurate are the calculators?

They're built for exactness — using precise NIST/BIPM conversion factors, published scientific and engineering formulas, and BigInt or exact-fraction math where rounding would otherwise creep in. Many categories were checked against authoritative sources (NASA, NOAA, USDA, King Arthur Baking and others), and the harder libraries are unit-tested.

Do I need to create an account?

Never. LazyTools has no accounts and holds no personal data — you just open a tool and use it. Some tools optionally remember your preferences in your browser's own local storage, which stays on your device.

Is LazyTools open source?

Yes — the site is open source on GitHub, so you can read exactly how every tool works and verify the privacy claims for yourself. It's a project of Synth88 Labs.