Tools

Child Growth (WHO)

Plot your child on the WHO 0–5y charts: z-score, percentile and saved growth path.

Heart Rate Zones

HRmax (Tanaka/Fox), 5 Karvonen zones, tap-to-measure and a beating-heart gauge.

BMI · BMR · TDEE

Body mass index with Asian cut-offs, resting energy and daily calorie needs.

Sleep Cycles

Enter wake-up (or bedtime) → the best bed/alarm times on 90-minute cycles.

Hearing Age Test

Hold to play pure tones 8→18 kHz, mark what you hear — get your “hearing age”.

Visual Acuity Test

Calibrate with a bank card, then a tumbling-E chart at true physical size — press where the E points; get 20/D, decimal & logMAR.

Reaction Time

Wait for green, click fast — 5 rounds, average & best in ms, personal record.

Colour Vision Test

10 dot-mosaic plates generated fresh each run — red-green & blue-yellow axes with a per-axis verdict.

BAC Estimator

Widmark estimate from drinks, weight and hours — clearance time and VN fine brackets.

Caffeine in Your Blood

Log phin coffee, milk tea, Red Bull by the hour — live decay curve, what's left right now & at bedtime.

VietQR / EMVCo QR

Decode a VietQR string field-by-field, or generate one with a QR image.

SWIFT MT Parser

Split {1:}…{5:} blocks, check the 16R/16S skeleton per message type and read MT 5xx status codes in plain words.

FIX Message Parser

Rebuild each order's lifecycle from a FIX 4.2/4.4 log, time every step and check session seq, PossDup and heartbeats.

Interest & Loan

See savings compound or work out a loan's monthly payment — with a live chart.

Income Tax & Insurance

Vietnam salary → insurance, personal income tax & net pay.

Effective Interest Rate

APR ↔ APY for any compounding — and compare deposit terms fairly on one chart.

FIRE Planner

Your FIRE number, years to independence and a net-worth chart racing to the goal.

Tax ID Validator & Lookup

Vietnam tax ID checksum step by step + registry lookup: name, address, status.

Electricity Bill (EVN)

5-tier tariff (Decision 14/2025) split per tier + VAT, cost curve, reverse from bill amount — editable prices.

Regex Tester

Write a pattern, watch every match light up, and read each symbol explained in plain words.

JSON Formatter

Pretty-print, validate and minify JSON; a collapsible tree with JSONPath, errors marked on their line.

JWT Decoder

Decode header & claims; verify HS with a secret or RS/PS/ES with the public key (PEM, JWK, JWKS).

UUID / ULID

Generate UUID v4/v7, ULID & NanoID — and read the embedded timestamp back.

Text Kit

Count words, diff two texts, and encode Base64 / URL / hashes — all in one.

Hash & Checksum

MD5, SHA-1/256/384/512, CRC32 & HMAC for text or a dropped file, checked against the published checksum.

CSV ↔ JSON

Two-way conversion with proper quote handling and a live table preview.

Unicode Inspector

Codepoints, UTF-8/16 bytes, hidden zero-width characters and NFC/NFD normalization.

VN Fake Data

Vietnamese test data — names, real phone prefixes, addresses… export CSV/JSON.

Markdown Preview

Split-pane live editor: tables, code blocks, lists — export clean HTML.

Cron Parser

Paste a cron expression: plain words, field breakdown, next runs in the server timezone and Vietnam time.

TOTP Generator

Base32 secret → live 2FA codes with countdown, otpauth:// QR.

SQL Formatter

Messy SQL → clauses on own lines, indented subqueries, highlighting; or minify.

URL Parser

Split scheme/host/path/hash, edit decoded query params and rebuild the URL.

JSON Diff

Structural diff: added/removed/changed keys with full paths, filter and copy.

Hex Viewer

Raw bytes: offset + hex + ASCII columns, magic numbers, hex/text search.

Hex ⇄ Text

Paste a hex stream, get text back: auto-detects UTF-16 BE/LE, UTF-8 or Latin-1.

String Escaper

Escape ⇄ unescape both ways: HTML entities, JSON string, URL component, \uXXXX.

Key Event Inspector

Press a key → event.key/code/keyCode, modifiers, plus a rollover/ghosting test.

Classical Ciphers

Caesar, Vigenère, Atbash, Rail fence & more — encode/decode both ways, plus break a cipher by letter-frequency analysis.

cURL ⇄ Code

Paste a curl command, get runnable fetch, axios and Go net/http code — or build a request and export clean curl.

JSON → TS / Go

Paste JSON, get TypeScript interfaces and Go structs — nested types named, optional fields detected, int/float told apart.

Scientific Calculator

A full expression calculator with functions, constants and a live graph.

Matrix Calculator

Add, multiply, invert… and watch a 2×2 transform the plane.

Number Base Converter

Convert between binary, octal, decimal and hex — watch the bits flip.

Unit Converter

Type a value and every unit converts live — length, mass, temperature, data and more.

Statistics

Paste numbers → summary stats, a histogram and a box plot.

Truth Table

Type a boolean expression → full truth table and classification.

Equation Solver

Quadratics, cubics, linear systems & regression — with a plot.

Percentage Calculator

X% of Y, percent change, increase/decrease and rule of three — instant answers.

Triangle Solver

SSS/SAS/ASA/AAS/SSA → all sides, angles, area & radii, drawn to scale.

Fractions

Add/multiply fractions and mixed numbers exactly with BigInt, steps included.

Primes & Divisors

Miller–Rabin tests, factorization, divisors, stepwise Euclid, sieve to 2M.

Roman Numerals

Two-way up to 3,999,999 with vinculum, symbol breakdown, flags sloppy forms.

Complex Numbers

Complex arithmetic, polar form, conjugates, nth roots — drawn on the plane.

Derivative & Integral

Type f(x) → plot f and f′, drag the tangent, shaded Simpson integral on [a,b].

Vector Playground

Drag two arrows: sum, difference, dot & cross product, angle and projection — picture and formulas always agree.

Logarithm

Fill 2 of 3 boxes in log_b(x)=y, the blank solves with steps — plus a draggable log-scale ruler and log laws with your numbers.

Modular Arithmetic

a mod n done right for negatives, exact BigInt: fast power, gcd, modular inverse — visualised on a clock dial.

Tonight's Star Map

A live star map for your location & time — bright stars, constellation figures, the Sun and Moon phase; slide the hours, or use GPS.

Periodic Table

Click any element for its configuration, isotopes and properties.

Wavelength · Color · Temp

Enter a wavelength and see its true color and black-body temperature.

Powers of Ten

See any size on the cosmic scale — from atoms to galaxies, side by side.

Gravity Calculator

Compute orbits, escape velocity and surface gravity for any world.

Fractal Explorer

Dive into the Mandelbrot and Julia sets with smooth WebGL zoom.

Resistor & Ohm's Law

Click the color bands to read a resistor — plus U·I·R·P from any two values.

Equation Balancer

Balance any chemical equation exactly — with molar masses & gram-to-gram math.

Braking Distance

Watch a car try to stop before a pedestrian — reaction + braking distance, road grip & impact speed.

pH & Dilution

pH ↔ ion concentrations on a color scale, C₁V₁=C₂V₂, mixing and solute weighing.

RC / LC Circuits

RC/RL cutoff with a live Bode plot, LC resonance, Xc/XL reactance at any f.

Decay & Dating

14 isotopes or custom T½ → remaining fraction after t, or age from % left (C-14).

Gear Ratio

Meshed gears spinning at true speed: teeth → ratio, torque × speed trade-off, idler flips direction.

Decibel Scale

From falling leaf to jet engine: intensity ratios, NIOSH safe listening time, why 60+60 dB = 63 dB, distance fall-off.

Ideal Gas PV=nRT

A living cylinder: drag the piston, heat the gas, solve any of P/V/n/T — Boyle & Charles traced on a P–V chart.

Lens & Mirror

Drag the object, three principal rays find the image live — real or virtual, camera to magnifier, 4 devices.

Projectile Motion

Drag to aim, fire, and watch range, peak and flight time live — with air drag, on Earth, the Moon or Mars.

Unix Timestamp

Convert Unix epoch ↔ dates, with a live ticking clock.

World Clock

Live clocks across cities + a slider to plan meetings across zones.

Pomodoro Timer

Focus in 25-minute sprints with breaks — a calm timer that keeps you on task.

Lunar Calendar & Almanac

Vietnamese lunar calendar (UTC+7): can-chi, lucky hours, Tết countdown, lunar anniversaries for 10 years ahead.

Date Difference

Years/months/days between two dates, working days — and date ± N days/months.

Age Calculator

Exact age, VN nominal age from real lunar years, zodiac and day-10,000 milestones.

Event Countdown

Big live countdown you can share as a link — Tết preset from the real lunar calendar.

Image Color Picker

Drop an image and pick any pixel's exact color — HEX, RGB, HSL, with a palette.

Color Contrast

Check text/background contrast against WCAG AA/AAA; when it fails, get the nearest passing colour.

Palette Maker

Build harmonious color palettes and export them as CSS or images.

Gradient Maker

Design linear, radial and mesh gradients — grab the CSS in a click.

Color Blindness Simulator

See any image through protan/deutan/tritan eyes, side by side with the original.

Image Resize & Compress

Resize, convert to JPEG/WebP/PNG, hit a size target like 500 KB, batch many images into a zip.

EXIF Viewer & Stripper

Reveal hidden photo metadata — camera, time, GPS — and download a cleaned copy.

Image → ASCII

Drop a photo and get character art — width, charsets, color mode, .txt export.

Font Preview

Your text in 30 system fonts or font files you drop in, A/B compare, all 134 Vietnamese letters checked.

Piano & Chords

Two playable octaves, chords & scales lighting up the keys with formulas, circle of fifths — pentatonic included.

QR Code Maker

Turn any text, link or Wi-Fi into a crisp QR code you can download.

Randomizer

Dice, coins, wheels and random picks — decide anything with a spin.

Sound Lab

Mix 8 harmonics into a timbre and watch waveform and spectrum change with every slider — or use your mic.

Password Generator

Generate strong, truly random passwords — pick length and character sets, see the strength.

Morse Code

Encode & decode Morse — then play it with real ITU timing and a blinking lamp.

Number to Words

Numbers → correct Vietnamese words, invoice style with “đồng”, and English.

Barcode Generator

Code 128 for any text + EAN-13 with auto checksum — crisp SVG, PNG export.

Typing Speed Test

Type VI/EN/number drills: WPM, accuracy, a live per-second chart and your best.

Text to Speech

Reads Vietnamese/English aloud sentence by sentence, lighting up the current sentence and word; click any sentence to start there.

Vietnamese Text Toolkit

Strip diacritics, switch old ↔ new tone styles, Telex/VNI → text, case, NFC.

🩺 Health