Khoa Nguyễn About Me!
Tools · ready to use

🧰 Tools

87 free tools that run right in your browser, sorted into eight shelves — health, finance & protocol decoders, dev & data helpers, time, color, math, science and everyday utilities. No install, no sign-up.

Health

Child Growth (WHO)

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

▶ Open

Heart Rate Zones

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

▶ Open

BMI · BMR · TDEE

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

▶ Open

Sleep Cycles

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

▶ Open

Hearing Age Test

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

▶ Open

Reaction Time

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

▶ Open

Colour Vision Test

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

▶ Open

BAC Estimator

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

▶ Open

Finance & protocols

VietQR / EMVCo QR

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

▶ Open

SWIFT MT Parser

Split {1:}…{5:} blocks and decode every field of securities MT 5xx messages.

▶ Open

FIX Message Parser

Decode raw FIX 4.2/4.4 messages into a readable table — enums, header/trailer and checksum.

▶ Open

Interest & Loan

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

▶ Open

Income Tax & Insurance

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

▶ Open

Effective Interest Rate

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

▶ Open

FIRE Planner

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

▶ Open

Tax ID Validator & Lookup

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

▶ Open

Electricity Bill (EVN)

6-tier tariff split per tier + VAT, cost curve, reverse from bill amount — editable prices.

▶ Open

Dev & data

Regex Tester

Write a pattern and watch every match light up — with capture groups listed live.

▶ Open

JSON Formatter

Pretty-print, validate and minify JSON — with syntax colors and error locations.

▶ Open

JWT Decoder

Decode the header & claims, and verify the HS256/384/512 signature.

▶ Open

UUID / ULID

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

▶ Open

Text Kit

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

▶ Open

Hash & Checksum

MD5, SHA-1/256/384/512, CRC32 & HMAC for text or a dropped file.

▶ Open

CSV ↔ JSON

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

▶ Open

Unicode Inspector

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

▶ Open

VN Fake Data

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

▶ Open

Markdown Preview

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

▶ Open

Cron Parser

Paste a cron expression: plain words, field breakdown and the next 10 runs.

▶ Open

TOTP Generator

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

▶ Open

SQL Formatter

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

▶ Open

URL Parser

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

▶ Open

JSON Diff

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

▶ Open

Hex Viewer

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

▶ Open

String Escaper

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

▶ Open

Key Event Inspector

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

▶ Open

Classical Ciphers

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

▶ Open

Time

Unix Timestamp

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

▶ Open

World Clock

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

▶ Open

Pomodoro Timer

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

▶ Open

Lunar ↔ Solar Calendar

Vietnamese lunar calendar (UTC+7): can-chi, leap months, solar terms & Tết countdown.

▶ Open

Date Difference

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

▶ Open

Age Calculator

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

▶ Open

Event Countdown

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

▶ Open

Color & design

Image Color Picker

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

▶ Open

Color Contrast

Check text/background contrast against WCAG AA/AAA, with a live preview.

▶ Open

Palette Maker

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

▶ Open

Gradient Maker

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

▶ Open

Color Blindness Simulator

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

▶ Open

Image Resize & Compress

Resize, convert to JPEG/WebP/PNG and watch the size drop.

▶ Open

EXIF Viewer & Stripper

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

▶ Open

Image → ASCII

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

▶ Open

Font Preview

Your text in 25+ system fonts, availability detection and close A/B compare.

▶ Open

Math & calc

Scientific Calculator

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

▶ Open

Matrix Calculator

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

▶ Open

Number Base Converter

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

▶ Open

Unit Converter

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

▶ Open

Statistics

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

▶ Open

Truth Table

Type a boolean expression → full truth table and classification.

▶ Open

Equation Solver

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

▶ Open

Percentage Calculator

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

▶ Open

Triangle Solver

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

▶ Open

Fractions

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

▶ Open

Primes & Divisors

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

▶ Open

Roman Numerals

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

▶ Open

Complex Numbers

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

▶ Open

Derivative & Integral

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

▶ Open

Science

Periodic Table

Click any element for its configuration, isotopes and properties.

▶ Open

Wavelength · Color · Temp

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

▶ Open

Powers of Ten

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

▶ Open

Gravity Calculator

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

▶ Open

Fractal Explorer

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

▶ Open

Resistor & Ohm's Law

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

▶ Open

Equation Balancer

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

▶ Open

Braking Distance

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

▶ Open

pH & Dilution

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

▶ Open

RC / LC Circuits

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

▶ Open

Decay & Dating

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

▶ Open

Utilities

QR Code Maker

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

▶ Open

Randomizer

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

▶ Open

Sound Lab

Generate a tone and watch its waveform and frequency spectrum live — or use your mic.

▶ Open

Password Generator

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

▶ Open

Morse Code

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

▶ Open

Number to Words

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

▶ Open

Barcode Generator

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

▶ Open

Typing Speed Test

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

▶ Open

Text to Speech

Your browser reads Vietnamese/English aloud, highlighting each word as it goes.

▶ Open

Vietnamese Text Toolkit

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

▶ Open