Convert between seconds, milliseconds, and date. 100% free, runs locally in your browser—nothing is uploaded to our servers.

Batch generate UUID v4 (crypto.randomUUID). 100% free, runs locally in your browser—nothing is uploaded to our servers.

Time-sortable unique ID, batch generate. 100% free, runs locally in your browser—nothing is uploaded to our servers.

Short random string with customizable alphabet. 100% free, runs locally in your browser—nothing is uploaded to our servers.

px/rem and byte KiB/MB conversions. 100% free, runs locally in your browser—nothing is uploaded to our servers.

Character reference for codes 0–127. 100% free, runs locally in your browser—nothing is uploaded to our servers.

Mod 97 check digit validation. 100% free, runs locally in your browser—nothing is uploaded to our servers.

Bank card number mod-10 validation. 100% free, runs locally in your browser—nothing is uploaded to our servers.

Parse and format to E.164 (libphonenumber-js). 100% free, runs locally in your browser—nothing is uploaded to our servers.

Phonetic alphabet, Morse code, and six-dot Braille. 100% free, runs locally in your browser—nothing is uploaded to our servers.

CODE128/EAN and other 1D barcodes (JsBarcode). 100% free, runs locally in your browser—nothing is uploaded to our servers.

TOTP two-factor authentication code generator. 100% free, runs locally in your browser—nothing is uploaded to our servers.

Generate Authorization header from username and password. 100% free, runs locally in your browser—nothing is uploaded to our servers.

Parse HTTP Cookie header string into table. 100% free, runs locally in your browser—nothing is uploaded to our servers.

Generate/edit JWT with custom header, payload, and secret. 100% free, runs locally in your browser—nothing is uploaded to our servers.

Generate SVG placeholder images with custom dimensions and colors. 100% free, runs locally in your browser—nothing is uploaded to our servers.

Online stopwatch: start/pause/reset/lap. 100% free, runs locally in your browser—nothing is uploaded to our servers.

Add/subtract days, calculate date intervals. 100% free, runs locally in your browser—nothing is uploaded to our servers.

Calculate age in years, months, days, and total days from birth date; optional reference date. 100% free, runs locally in your browser—nothing is uploaded to our servers.

Generate random integers or decimals in a range (up to 500), copy with one click. 100% free, runs locally in your browser—nothing is uploaded to our servers.

Percentage calculations. 100% free, runs locally in your browser—nothing is uploaded to our servers.

Convert between °C, °F, K temperature units. 100% free, runs locally in your browser—nothing is uploaded to our servers.

Convert between Arabic and Roman numerals. 100% free, runs locally in your browser—nothing is uploaded to our servers.

Look up vendor by MAC prefix (OUI). 100% free, runs locally in your browser—nothing is uploaded to our servers.

Calculate CIDR notation from IP range. 100% free, runs locally in your browser—nothing is uploaded to our servers.

Common port numbers and protocols reference. 100% free, runs locally in your browser—nothing is uploaded to our servers.

Evaluate math expressions with functions and constants. 100% free, runs locally in your browser—nothing is uploaded to our servers.

Estimate remaining time from progress and elapsed time. 100% free, runs locally in your browser—nothing is uploaded to our servers.

Generate random MAC addresses with prefix and case options. 100% free, runs locally in your browser—nothing is uploaded to our servers.

Detect browser, screen, network and system information. 100% free, runs locally in your browser—nothing is uploaded to our servers.

Estimate token count for GPT-4/GPT-3.5/Claude models. 100% free, runs locally in your browser—nothing is uploaded to our servers.

Calculate simplest ratio and reverse compute from known side. 100% free, runs locally in your browser—nothing is uploaded to our servers.

Equal installment / equal principal with payment schedule. 100% free, runs locally in your browser—nothing is uploaded to our servers.

Calculate BMI value and category with reference chart. 100% free, runs locally in your browser—nothing is uploaded to our servers.

Calculate work duration, overtime, and salary estimate. 100% free, runs locally in your browser—nothing is uploaded to our servers.

China cumulative withholding tax calculation. 100% free, runs locally in your browser—nothing is uploaded to our servers.

WGS84/GCJ-02/BD-09 coordinate system conversion. 100% free, runs locally in your browser—nothing is uploaded to our servers.

SRT/WebVTT/ASS subtitle format conversion. 100% free, runs locally in your browser—nothing is uploaded to our servers.

Greatest common divisor & least common multiple. 100% free, runs locally in your browser—nothing is uploaded to our servers.

Fullscreen scrolling danmaku, custom speed/color. 100% free, runs locally in your browser—nothing is uploaded to our servers.

Batch generate new filenames by rules. 100% free, runs locally in your browser—nothing is uploaded to our servers.

Look up issuing bank by first 6 digits. 100% free, runs locally in your browser—nothing is uploaded to our servers.

Offline currency exchange rate converter. 100% free, runs locally in your browser—nothing is uploaded to our servers.

Web Audio API audio trimming with waveform preview. 100% free, runs locally in your browser—nothing is uploaded to our servers.

Parse .torrent files, convert to magnet link. 100% free, runs locally in your browser—nothing is uploaded to our servers.

Generate placeholder images with custom size and color.

Generate app privacy policy documents.

Pomodoro technique timer.

Artistic QR codes with dot styles and gradient colors.

Calculate PPI from screen diagonal and resolution.

Equal payment / equal principal repayment schedule.

View GB2312/GBK Chinese encoding table.

Convert between solar and lunar calendar dates.

Display current time in multiple cities/time zones.

Detect mic devices, record & playback with volume visualization. 100% free, runs locally in your browser—nothing is uploaded to our servers.

Press keys to highlight virtual keyboard, display key code and modifier info. 100% free, runs locally in your browser—nothing is uploaded to our servers.

Full-screen solid colors for dead pixel testing, view resolution & pixel ratio. 100% free, runs locally in your browser—nothing is uploaded to our servers.

Online drawing board with color picker, brush size, eraser, undo, clear, and PNG export. 100% free, runs locally in your browser—nothing is uploaded to our servers.

Calculate base^exponent mod modulus with BigInt support. 100% free, runs locally in your browser—nothing is uploaded to our servers.

Reverse bits at specified width, showing original, reversed, hex and decimal results. 100% free, runs locally in your browser—nothing is uploaded to our servers.

Check if a year is a leap year, or list all leap years in a range. 100% free, runs locally in your browser—nothing is uploaded to our servers.

Preview text in different fonts, supports web-safe fonts and custom font-family. 100% free, runs locally in your browser—nothing is uploaded to our servers.

Read and display clipboard content with multiple MIME types. 100% free, runs locally in your browser—nothing is uploaded to our servers.

Simple SVG visual editor supporting rect, circle, ellipse, line, text shapes. 100% free, runs locally in your browser—nothing is uploaded to our servers.

Test your reaction speed, track history with average, best and worst stats. 100% free, runs locally in your browser—nothing is uploaded to our servers.

Convert between IPv4 and IPv6 formats: mapped, compatible, 6to4 and more. 100% free, runs locally in your browser—nothing is uploaded to our servers.

Set up automatic page refresh at intervals, with iframe preview and bookmarklet. 100% free, runs locally in your browser—nothing is uploaded to our servers.