Johny Kvsky DevTools

Small browser-based developer tools for common data formats and identifiers.

Demo: https://johnykvsky.github.io

Tools

• JSON Formatter: validate, format, minify, clean non-ASCII characters, toggle output word wrap, and copy formatted output.
• JSON Compare: validate and compare two JSON documents with formatted output, highlighted differences, and a change list.
• Base64 Encoder / Decoder: encode and decode Base64 strings locally, including UTF-8 text.
• JWT Encoder / Decoder: decode JWT header and payload, inspect registered claims and time status, verify signatures, and encode/sign tokens.
• UUID Generator: generate secure UUID v4 and UUID v7 values, validate UUID v1-8 strings, and inspect timestamp details for time-based UUIDs.
• Timestamp Converter: convert Unix timestamps to dates and dates to Unix timestamps, including timezone-aware date inputs.

Design Goals

• Pure vanilla JavaScript.
• Browser-only processing; input data is not sent to a server.
• Lightweight CSS with responsive layouts for desktop and mobile.
• No jQuery, Bootstrap, or heavy frontend framework.
• Shared UI toolkit for common layout, status, copy, and dark/light theme behavior.

JWT Support

JWT decoding works for standard three-part JWT tokens.

Signature verification supports:

• HMAC secrets: HS256, HS384, HS512
• PEM public keys: RS256, RS384, RS512, PS256, PS384, PS512, ES256, ES384, ES512

Token encoding/signing supports:

• Unsigned tokens: none
• HMAC secrets: HS256, HS384, HS512
• PEM PKCS#8 private keys: RS256, RS384, RS512, PS256, PS384, PS512, ES256, ES384, ES512

HMAC signing key length is validated before encode according to RFC 7518 minimums.

Local Checks

Run the smoke checks:

node tests/smoke.js

The smoke test checks current tool pages, shared assets, script syntax, sample JWT decoding, UUID v7 shape, and UTF-8 Base64 behavior.

License

The MIT License (MIT). See LICENSE.md.