chekkutooru

See exactly which keys your keyboard registers when you mash several at once.

Click the instant the panel turns green. Measured to the millisecond.

Count how many fingers your screen tracks at the same time.

Unroll the test scroll and measure dropped frames, event rate, and wheel step.

Press every button and wiggle both sticks to verify inputs, triggers, and drift.

Mash the pad for ten seconds and measure your clicks per second.

Time your click intervals and catch a worn switch firing phantom doubles.

Draw with your pen and watch pressure and tilt readings live.

Press a few keys and let the browser deduce your keyboard layout.

Check what clipboard read and write access this browser grants.

A bubble level driven by your phone's gyroscope and accelerometer.

Flood your screen with solid colors to hunt for dead or stuck pixels.

Measure your display's real refresh rate and judge motion clarity.

Step wedges and gamma patterns to dial in your monitor by eye.

Resolution and diagonal in, aspect ratio and pixel density out.

Compare body text sizes on your own screen at your own distance.

Estimate your browser zoom level and effective DPI right now.

Your resolution, viewport, pixel ratio, and orientation at a glance.

Check any text and background pair against WCAG AA and AAA, live.

Paste your whole palette and get a WCAG contrast matrix for every color pair.

Preview your colors or an image the way protan, deutan, and tritan vision sees them.

Play tones from 125 Hz to 20 kHz and find where your hearing stops.

Left, right, both: confirm your channels aren't swapped.

A live level meter for your microphone. Analysed locally, never recorded.

Read your audio stack's latency and tap along to feel the delay.

A live round-trip-time graph with jitter and loss counters.

See how much site storage your browser is using and what's left.

Everything a site can silently learn about your browser, listed.

Identify your GPU and its WebGL limits, with a live render check.

Inspect this site's cookies, localStorage, and sessionStorage.

Peek at JS heap usage and estimate your comfortable tab budget.

Test patterns live with match highlighting and a plain-English breakdown.

Fluid typography clamp() values computed and previewed live.

Build a cron schedule and read it back in plain English.

Draft Open Graph tags and preview how link cards will read.

Dial in box-shadows, gradients, and radii visually; copy the CSS.

Preview a page inside common device viewport sizes.

Paste HTML and see the keyboard tab order, with anti-pattern flags.

Validate, pretty-print, or minify JSON with pinpointed errors.

Compare two texts line by line with added and removed highlights.

Placeholder text on demand, in classic Latin or kanji-flavored filler.

Crypto-random UUIDs and short IDs, generated in your browser.

Type Markdown on the left, read the rendered page on the right.

Convert text to Base64 and back, UTF-8 safe, entirely offline.

Paste HTML and flag images with missing or lazy alt text.

Outline your H1-H6 hierarchy and catch skipped levels.

Spot broken references, missing names, and redundant roles.

Thirty seconds of shrinking targets. Accuracy, speed, and score.

A gently judgmental record of your time on this very page.

Watch your battery level and estimate the drain per hour.

Write 漢字[かんじ] and get rendered ruby plus copyable HTML.

Ten quick questions on stroke counts and meanings, N5-N4.

Hiragana and katakana flashcards with streaks and weak-spot review.