Labs

Cron Builder

Write a cron expression, get a human-readable description + next 5 runs + interactive field builder. Sanity-check yourself when wiring QStash / GitHub Actions / Kubernetes CronJobs.

cron · scheduling · qstash

HMAC Lab

Key + message → tag. See the difference between naive `===` and constant-time tag comparison — why timing attacks are a real threat, visualised.

hmac · mac · timing-attack · sha-256

HTTP Header Analyzer

Paste response headers, get a security score. CSP / HSTS / Permissions-Policy / X-Frame-Options parsed, missing headers flagged, directives explained in plain language.

http · security · csp · headers

Timezone Converter

Show multiple timezones side-by-side, change one and all sync. DST transitions flagged, work-hour overlap/gap color-coded. Cross-region meeting coordination.

timezone · datetime · intl

AEAD Tamper Demo

Encrypt with AES-256-GCM, flip a single byte of the ciphertext, watch decryption fail with "authentication failed". Explains *why* you need authenticated encryption in one click.

aes-gcm · aead · tamper-detection · webcrypto

Base64 Encoder / Decoder

Bidirectional text ↔ base64. Standard and URL-safe variants, one-click direction swap. UTF-8 safe (handles non-ASCII characters).

base64 · encoding · web

ChaCha20 Inner State Stepper

Step through the 4×4 state matrix of ChaCha20 quarter-round by quarter-round. Set key and nonce, watch which cells change in each of the 320 sub-ops.

chacha20 · stream-cipher · rfc-7539

CIDR Subnet Calculator

From an IPv4 CIDR input, computes network address, broadcast, first/last usable host, host count, subnet mask, and a binary breakdown. Classifies the address (RFC 1918, loopback, link-local).

networking · cidr · subnet · ipv4

Color Contrast (WCAG)

Pick foreground + background colors, compute the contrast ratio, see WCAG AA / AAA pass/fail live. Separate verdicts for normal and large text.

accessibility · wcag · color · contrast

CSS Specificity Calculator

Paste two selectors, see the (a, b, c) tuple, learn which one wins. Token-by-token color breakdown. Correctly handles `:where()`, `:not()`, `:is()`, and `:has()`.

css · specificity · selectors

Cubic-Bezier Tester

Shape a cubic bezier curve with two control points, scrub the timeline, watch how easing *distorts* time. Copy the CSS value, done.

css · animation · easing

Diff Viewer

Compare two pieces of text side-by-side or unified. LCS-based line diff with optional whitespace-ignore. Code review, manifest comparison, content drift.

diff · version-control · comparison

JSON Formatter

Paste JSON, get pretty-printed output + an interactive collapsible tree. Errors land with line/column position; minify and indent options included.

json · formatter · validator

auth

JWT Decoder + Verifier

Paste a JSON Web Token, split into header / payload / signature, verify with an HMAC secret. Auto-flags expired, not-yet-valid, and dangerous "alg none" tokens.

jwt · jose · hmac · hs256

auth

JWT Generator

Payload + secret + algorithm → signed JWT. The reverse of JwtDecoder. HS256/384/512, auto-regenerate on input change, exp/iat/nbf claim helpers.

jwt · jose · hmac · hs256

Password Entropy Meter

Compute password strength via Shannon entropy. Detect character classes, project crack time for four attacker profiles. Nothing leaves your browser.

password · entropy · security

Regex Tester

Pattern + flag chips, live match highlighting, capture group breakdown, replacement preview. Everything runs in your browser — patterns never leave the page.

regex · validation · search

SHA-2 Hash Lab

Live SHA-1, SHA-256, SHA-384 and SHA-512 in the browser. Watch the avalanche effect at bit level — change one character and roughly half the output bits flip.

sha-256 · sha-512 · hash · webcrypto