Free Developer Tools
A fast, private toolkit built for engineers — format and validate JSON, decode JWTs, test regular expressions, generate UUIDs, convert JSON to TypeScript and more. Every tool runs entirely in your browser: no signup, no uploads, and whatever you paste never leaves your device.
Runs entirely in your browser — nothing is uploadedJSON & Data
Encoding & Security
Base64 Encoder & Decoder
Encode and decode Base64 text instantly, with full UTF-8 support.
encode · decode · UTF-8
JWT Decoder & Inspector
Decode and inspect JWT header, payload and claims — locally, never sent anywhere.
header · payload · exp
URL Encoder & Decoder
Percent-encode and decode URLs and query components safely.
percent-encode
Hash Generator
Generate SHA-1, SHA-256, SHA-384 and SHA-512 hashes in your browser.
SHA-1/256/384/512
Generators
UUID Generator
Generate cryptographically-random UUID v4s in bulk, with one-click copy.
v4 · bulk · crypto
QR Code Generator
Create QR codes for a URL, text, Wi-Fi, email or phone and download as PNG or SVG.
url · wifi · png/svg
Password Generator
Generate strong, cryptographically-random passwords with custom length, character sets and a strength meter.
strong · crypto · custom
Random Number Generator
Generate random numbers in a range, with integers or decimals, uniqueness and secure randomness.
range · unique · crypto
Converters
JSON to TypeScript
Turn any JSON into clean, nested TypeScript interfaces instantly.
interfaces · nested
SVG to React Component
Convert raw SVG markup into a typed React component.
jsx · typed · props
Unix Timestamp Converter
Convert Unix/epoch timestamps to human dates and back, in seconds or milliseconds.
epoch · UTC · ISO
Number Base Converter
Convert numbers between binary, octal, decimal, hexadecimal and any base 2–36.
bin · oct · dec · hex
Color Converter
Convert colors between HEX, RGB, HSL and HSV with a live preview.
hex · rgb · hsl
JSON to CSV Converter
Convert JSON to CSV and CSV back to JSON, with proper quoting and headers.
json ⇄ csv
Web & SEO
Robots.txt Generator
Build a valid robots.txt with allow/disallow rules and a sitemap line.
allow · disallow · sitemap
Sitemap Generator
Generate an XML sitemap from a list of URLs.
urls → xml
Schema Markup Generator
Generate JSON-LD structured data for common schema.org types.
json-ld · rich results
Open Graph Preview
Preview how a page looks when shared on social platforms and generate OG meta tags.
share card · meta tags
Color Palette Extractor
Extract a dominant colour palette from any image and copy HEX/RGB values.
image → hex · rgb
Formatters & Minifiers
SQL Formatter
Format and beautify SQL queries with consistent indentation.
mysql · postgres · more
HTML Minifier
Minify HTML to shrink page weight.
strip · collapse
CSS Minifier
Minify CSS for faster loads.
compress · size report
JavaScript Minifier
Minify JavaScript with Terser to reduce file size.
terser · mangle
SVG Optimizer
Clean and shrink SVG files without losing quality.
clean · preview
Why run developer tools in the browser?
Most online dev utilities are thin front-ends over a server endpoint. You paste, it POSTs, a machine you do not control parses your input and returns a result. For a lorem-ipsum string that is harmless. For a signed JWT from staging, a customer record inside an API response, or a private key fingerprint, it means production data has left your network and landed in someone else's logs.
Every tool here is plain JavaScript executing in your own tab. There is no upload step, no request to inspect, and no server-side copy to retain — which also means there is no breach surface later. That is a claim you can verify rather than trust: open DevTools, watch the Network tab, and use any tool on this page. You will not see a request carrying your input.
The practical side effects are worth having too. Nothing round-trips, so results are instant. There is no rate limit, because there is no server to protect. And once a page has loaded, it keeps working without a connection.
Finding the right tool
Working with JSON and data. The JSON formatter and validator is the one most people arrive for — it beautifies, minifies and reports the exact position of a syntax error. From there, JSON to TypeScript turns a sample payload into typed interfaces, and JSON to CSV converts in both directions with correct RFC-4180 quoting. For pattern work, the regex tester highlights matches and capture groups as you type.
Encoding and security. The JWT decoder splits a token into header, payload and signature and surfaces expiry and standard claims — locally, which matters more here than anywhere else on the site. Alongside it sit Base64 encode and decode with full UTF-8 support, a SHA hash generator, and a URL encoder for safe percent-encoding of query components.
Generating things. Bulk UUID v4 generation and the password generator both use the Web Crypto API rather than Math.random(), so the output is cryptographically random. The QR code generator exports PNG or SVG with no tracking redirect and no expiry.
Converting formats. Everyday conversions live in Unix timestamp, number base and colour converters. If your work is more documents than data, the text tools and PDF tools follow the same no-upload rule.
Frequently asked questions
Are these developer tools really free?
Yes — every tool on this page is free with no signup, no account and no usage cap. There is no paid tier holding features back.
Is it safe to paste a JWT or API response into an online tool?
Into most online tools, no — they post your input to a server, which means a production token or customer data leaves your machine. These tools are different: every one runs as JavaScript in your own browser, so what you paste is never transmitted anywhere. You can confirm it by opening DevTools and watching the Network tab while you use them.
Do these tools work offline?
Mostly yes. Once a tool page has loaded, the processing itself needs no network, so it keeps working if your connection drops. The site also registers a service worker, so previously visited tools can load again offline.
Is there a file size or request limit?
There is no artificial limit. Because the work happens on your own device, the practical ceiling is your browser's available memory rather than a quota we impose.
Do you store or log what I paste?
No. There is no server-side processing to log. Input stays in the page's memory and is discarded when you close or reload the tab.
Which tool should I use to validate JSON?
Use the JSON Formatter — it validates as it formats and points at the exact line and character where parsing failed, which is usually a trailing comma, a single quote, or an unescaped character inside a string.
Explore more free tools
Every category runs free in your browser — nothing is uploaded.