UsefulTab
Developer
Encoders, formatters, hashes, and generators for everyday dev work.
29 tools in this category, all running locally in your browser.
A grab-bag of everyday developer utilities: format and validate JSON, encode and decode Base64 and URLs, escape HTML entities, decode JWTs, generate UUIDs and QR codes, test regular expressions, convert Markdown to HTML, explain cron expressions, and more. Each one loads instantly and runs client-side, so you can decode a token or pretty-print a payload without pasting it into a random website that phones it home — nothing you enter leaves your browser.
JSON Formatter
Format, minify, and validate JSON in your browser.
Base64 Encoder / Decoder
Encode text to Base64 or decode it back, UTF-8 safe.
URL Encoder / Decoder
Percent-encode or decode URI components with an encode/decode toggle.
HTML Entities Encoder / Decoder
Encode text to HTML entities or decode entities back to characters.
JWT Decoder
Base64url-decode a JWT to inspect its header and payload claims.
UUID Generator
Generate cryptographically random v4 UUIDs in bulk.
ULID Generator & Decoder
Generate 1–100 monotonic, lexicographically sortable ULIDs from secure randomness, and decode any ULID back to its millisecond timestamp and ISO date.
Color Palette & Gradient Generator
Pick a base color to generate harmonious palettes and a CSS linear gradient, with copyable hex codes and CSS — all locally.
QR Code Generator
Generate a QR code from text or a URL and download it as PNG or SVG.
Random Number Generator
Pick a min, max, and how many numbers to generate — with an option to disallow duplicates.
CSS / JS / HTML Minifier
Strip comments and whitespace from CSS, JS, or HTML and see how much you saved.
Side-by-Side Diff Viewer
See two versions of a text side by side, aligned line-by-line with changes highlighted.
Regex Tester
Write a regex, pick flags, and see every match highlighted with capture groups.
Markdown to HTML
Write Markdown and get clean HTML, with a live rendered preview — no upload.
Cron Expression Explainer
Turn a cron expression into plain English and preview when it runs next.
LLM Token Counter
Estimate token counts and context-window usage for GPT, Claude, and Gemini — all locally.
JSON to Types
Paste JSON and get TypeScript interfaces, Zod schemas, or Python Pydantic models.
cURL to Code
Paste a cURL command and convert it to JavaScript fetch, axios, or Python requests.
Chmod Calculator
Tick read/write/execute for owner, group, and public to get the octal and symbolic chmod.
SVG Blob & Wave Generator
Generate customizable SVG blobs and wave section dividers with copyable markup and CSS.
IPv4 Subnet Calculator
Enter an address and CIDR to get the network and broadcast addresses, subnet and wildcard masks, usable host range and count, IP class, and a binary view.
IPv4 Converter
Convert an IPv4 address live between dotted-decimal, dotted-binary, hex, 32-bit integer, and IPv6-mapped form — edit any field to update the rest.
MAC Address Tool
Generate random, valid, locally-administered MAC addresses with casing, separator, and prefix options, plus an honest vendor lookup over a small built-in OUI sample.
URL Parser & Query Editor
Split a URL into protocol, host, port, path, and hash, then add, edit, or remove query parameters in a table that rebuilds the URL instantly.
User-Agent Parser
Detect your own browser's User-Agent or paste any UA string to break out browser, engine, OS, CPU, and device type with a dependency-free parser.
Open Graph Generator
Fill in title, description, URL, and image to get copy-ready Open Graph and Twitter Card meta tags with a live preview of the share card.
QR Code Scanner
Decode QR codes from your camera or an uploaded image, locally.
Barcode Generator
Create barcodes (Code128, EAN, UPC, Code39) and download SVG or PNG.
SVG Viewer & Optimizer
Preview, clean up, and minify SVG markup right in your browser.
Developer guides
How to encode and decode Base64, read a JWT, format and validate JSON, test regular expressions, and generate UUIDs and QR codes.
Encode & decode Base64
What Base64 is, when you actually need it, and how to encode or decode text and images in your browser without uploading anything.
Test a regular expression
Build and debug a regex against live sample text, understand flags and capture groups, and avoid the mistakes that trip people up — privately in your browser.
Generate a UUID
Generate UUIDs, understand v4 vs. v1, and know when a ULID is the better choice for sortable IDs — generated in your browser, never on a server.
Format and validate JSON
Pretty-print messy JSON, catch syntax errors, and understand common validation failures — all in your browser with nothing uploaded.
Create a QR code
Generate a QR code for a link, text, or Wi-Fi, keep it scannable, and know what it can and can't do — made in your browser with nothing uploaded.
Decode a JWT safely
Read the header and payload of a JSON Web Token, understand its claims, and why decoding is not the same as verifying — all locally.
Common questions
Is it safe to decode a JWT or token here?
Yes. The JWT decoder and every other tool run entirely in your browser. Tokens, payloads, and keys you paste are never sent to a server, so they stay on your device.
Do these tools work offline?
Mostly. Your input is never sent anywhere, and most tools keep working if your connection drops after the page has loaded. A few (Markdown to HTML, the barcode generator and the QR scanner) download a library the first time you use them, so that first use needs a connection. A tool you have used before reopens offline in the same browser.
Do you store anything I generate?
No. UUIDs, QR codes, formatted output, and everything else are produced in the browser and never recorded or transmitted.