Clinical Vision & Hearing Tests.
Plus Fast Creator Utilities. Always Free.
Scientifically validated sensory screening tools and sharp digital utilities. 100% private client-side processing, instant browser calibration, and zero registration required.
Clinical Sensory & Perception Labs
Visual Contrast Sensitivity Test
Screen for subtle contrast loss, night driving glare, and visual pathway fatigue using the official clinical Pelli-Robson Log CS benchmark.
Hearing Age & High-Frequency Test
Determine your biological ear age by evaluating your upper auditory limit (8 kHz - 20 kHz). Test high-frequency presbycusis and mosquito tones.
Tinnitus Pitch Matcher & Masker
Pinpoint the exact pitch of your ear ringing (250 Hz - 16 kHz) and generate customized notched sound therapy maskers to soothe phantom audio perception.
JND Color Perception Test
Scientific Delta-E color perception benchmark. Measure your visual cone photoreceptor threshold and discover your exact color discrimination acuity.
Creator & Visual Media Utilities
Safe Zone Visualizer
Interactive tool to preview 9:16 vertical video safe zones and download overlay templates for TikTok, Instagram Reels, and YouTube Shorts.
Barcode Studio
Generate professional 1D barcodes for Code 128, Code 39, UPC-A, and EAN-13 product labeling with high-resolution export.
Username Checker
Check username availability simultaneously across GitHub, Reddit, Twitter/X, Instagram, TikTok, and YouTube in real time.
Words to Pages Calculator
Accurately convert word counts to printed pages based on font family, point size, line spacing, and margin presets.
Color Memory Challenge
Test your chromatic visual memory. Memorize a target hue and test how accurately you can recreate it using HSL sliders.
Developer & Web Utilities
CSS Clamp Calculator
Generate responsive fluid typography rules instantly with dynamic viewport slope calculations.
JSON Formatter & Validator
Format, validate, and minify JSON strings with real-time error detection and syntax hierarchy.
Image Optimizer
Compress and convert images to WebP, PNG, or JPG directly in your browser without quality loss.
Password Generator
Generate cryptographically secure random passwords and passphrases with entropy scores.
QR Code Generator
Create professional, permanent vector QR codes for URLs, WiFi, and contact vCards instantly.
Color Picker & Palettes
Pick and convert colors between HEX, RGB, HSL, and CMYK with harmonious palette generation.
100 Worst Passwords
Inspect the globally ranked top 100 most cracked passwords and see how fast each falls to brute-force attacks.
Word & Character Counter
Count words, characters, sentences, reading time estimates, and keyword density stats.
Text Case Converter
Transform strings between UPPERCASE, lowercase, Title Case, camelCase, snake_case, and kebab-case.
Unit Converter
Convert units across length, weight, temperature, area, digital storage, and speed instantly.
URL Encoder / Decoder
Safely encode and decode URI components for APIs, query strings, and web development.
Base64 Encoder / Decoder
Encode plain text or binary files to Base64 format and decode Base64 strings back to text.
Hash Generator
Generate cryptographic checksums including MD5, SHA-1, SHA-256, and SHA-512 from any input.
GBP Triage Tool
Audit Google Business Profile compliance and prepare evidence packs for reinstatement appeals.
Clinical Science & Research Library
In-depth guides on psychophysics, auditory biomechanics, and color perception algorithms written for researchers and curious minds.
Pelli-Robson Contrast Sensitivity: The Clinical Guide
Why standard 20/20 Snellen acuity tests miss functional vision deficits, how Log CS thresholds are scored, and causes of contrast loss.
Read clinical guideUnderstanding Just Noticeable Difference (JND) in Vision
How the Weber-Fechner law and CIELAB Delta-E color distance formulas measure the exact boundary of human sensory perception.
Read research articleWhy sRGB is Dying: Wide Gamut Displays & Oklab
Why modern Display P3 monitors and CSS Color 4 spaces are rendering legacy 1996 sRGB obsolete for creative professionals.
Read display guideFrequently Asked Questions
What is HandleKit?
HandleKit provides free, scientifically validated sensory screening labs—such as the clinical Pelli-Robson Contrast Sensitivity Test, Hearing Age biological threshold test, and Tinnitus sound therapy matcher—alongside professional creator and developer utilities. Everything runs in the browser without sign-ups.
Are the sensory and screening tools clinically accurate?
Yes. Our Contrast Sensitivity Test implements the official Pelli-Robson Log CS psychophysical benchmark, while our Hearing Age screener uses calibrated high-frequency tone synthesis (8 kHz to 20 kHz) to evaluate presbycusis. While not a substitute for an in-person medical diagnosis, they offer reliable, high-precision preliminary screenings.
Is my data private?
Privacy is fundamental to HandleKit. All sensory calculations, audio synthesis, password generation, and conversions execute 100% locally in your browser using Web Audio, Canvas, and WebAssembly APIs. Your personal inputs and test scores never leave your device.
Are all tools permanently free?
Yes, completely and permanently free. There are no premium tiers, subscriptions, paywalls, or trial periods. You will never be asked for an email address or credit card.
Can I suggest a new tool or screening assessment?
Absolutely. Send your ideas to contacthandlekit@gmail.com or use the contact page. New tools are developed based on community needs.