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KelvidoWeb & Developer Tools

Web & Developer Tools

Small, focused utilities for building and securing things online — encoding, hashing, ID generation, JSON, and more. Each one does exactly one job well.

Encoding & Data

Base64 Encoder / Decoder

Encode or decode Base64 text — Standard (RFC 4648, + / with = padding) or URL-safe (- _, no padding, the variant used in JWTs) — type in either box and the other updates instantly.

Encoding & Data Local processing

URL Encoder / Decoder

Encode or decode a URL component (RFC 3986, spaces as %20) or a form value (application/x-www-form-urlencoded, spaces as +) — type in either box and the other updates instantly.

Encoding & Data Local processing

Hash Generator

Instantly compute SHA-1, SHA-256, SHA-384, and SHA-512 hashes of any text using your browser's built-in crypto.subtle. MD5 isn't offered — it's not part of the Web Crypto API.

Encoding & Data Local processing

JSON Formatter & Validator

Validate JSON against the RFC 8259 spec with exact line/column error reporting, then pretty-print or minify it — with warnings for duplicate keys and unsafe-precision numbers.

Encoding & Data Local processing

Image to Base64 Converter

Convert an image to a Base64 string or data URI, or decode one back into a downloadable image.

Encoding & Data Local processing

Generators

Password Generator

Generate strong, random passwords with your browser's cryptographically secure random number generator, with a real entropy-based strength rating.

Generators Local processing

UUID Generator

Generate random Version 4 UUIDs (RFC 4122) using your browser's built-in crypto.randomUUID() — bulk-generate, with optional uppercase and no-hyphens formatting.

Generators Local processing

Slug Generator

Type a title to get a clean, URL-safe slug instantly — lowercased, accents stripped (café → cafe), punctuation collapsed into a hyphen or underscore.

Generators Local processing

Lorem Ipsum Generator

Generate Lorem Ipsum placeholder text by paragraphs, sentences, or words.

Generators Local processing

Developer Utilities

JWT Decoder

Decode a JSON Web Token’s header and payload. This tool never verifies the signature — decoding is not proof a token is valid.

Developer Utilities Local processing

Regex Tester

Test a regular expression against your own text with live match highlighting, capture groups, and named groups.

Developer Utilities Local processing

Cron Expression Parser

Parse a standard 5-field cron expression into a plain-English schedule.

Developer Utilities Local processing

WCAG Contrast Checker

Check the contrast ratio between two colors against WCAG 2.2 AA and AAA thresholds for normal and large text.

Developer Utilities Local processing

Meta Tag Generator + OG Preview

Generate title, description, Open Graph, and Twitter/X Card meta tags with an approximate search and social preview.

Developer Utilities Local processing

Converters

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Markdown → HTML

Paste Markdown to see it rendered live and get the HTML source to copy — CommonMark + GFM tables/strikethrough, raw HTML always shown as text, never executed.

Converter Local processing

HTML → Markdown

Paste HTML to get clean Markdown instantly — headings, links, lists, code, blockquotes, GFM tables and strikethrough. Script and style content is always dropped.

Converter Local processing

JSON ⇄ YAML

Convert between JSON and YAML instantly, in either direction — type in either box and the other updates. Reuses the JSON Formatter validator for accurate line/column error messages.

Converter Local processing

Image

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QR Code Generator

Type or paste a URL or any text to get a QR code instantly, ready to download.

Image Local processing

Image Dimension Checker

Upload any image to instantly see its exact width, height, aspect ratio, format, file size, and megapixel count.

Image Local processing

Calculators

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Percentage Calculator

Find a percentage of a number, what percent one number is of another, percent increase/decrease, or the original number before a percentage was applied.

Calculator Local processing

More

JSON to TypeScript

Paste a JSON response to generate TypeScript interfaces for it — nested objects, arrays, optional keys, and nullable values included.

Local processing

Why these tools run entirely in your browser

Passwords, API keys, hashes, and the data you encode or format here are exactly the kind of thing that shouldn't touch a server you don't control. Every tool on this page runs locally in JavaScript — nothing is uploaded, logged, or stored.