About Deftkit

What this is

Deftkit is a small, focused collection of 36 everyday utilities for developers, designers, and ops people. Format some JSON. Decode a JWT. Generate a strong password. Convert a Unix timestamp. Pick a color and check its contrast. The kind of one-off chores you reach for several times a week and want to finish in five seconds without leaving the browser.

Every tool here is built around three principles. They sound obvious, and they explain almost every design decision on the site.

1. Everything runs in your browser

Not "most of the time". Not "except for analytics". Every tool processes its input entirely on your device. There is no upload, no server round-trip, no log of what you typed. You can paste a production API token into the JWT decoder, hash a sensitive string, generate a master password, or convert a private contract date — and the value never leaves your machine. The browser is the backend.

This is a deliberate choice. The internet is full of "free" tools that quietly send everything you type to a server somewhere. For most casual tasks that's harmless. For passwords, tokens, internal URLs, financial data, and proprietary content, it is not.Deftkit is designed so you never have to think about the difference. You can use it for anything.

2. Simple and fast, on purpose

The site loads instantly. Every tool page is statically pre-rendered, ships only the JavaScript its widget actually needs, and works on slow connections. There are no popups, no cookie banners begging you to accept tracking, no "sign up for our newsletter" modals. Open the page, do the thing, close the tab. That's the entire experience.

Each tool is also intentionally narrow. The JSON formatter formats JSON. It doesn't also try to be a JSON-to-CSV converter and a schema generator and a query builder. Doing one thing well is more useful than doing twelve things badly.

3. SEO-friendly so good tools find their users

The web is full of tools that work great but nobody can find. Every page on Deftkitis built so search engines can index it properly: clean URLs, server-rendered HTML, structured data, fast Core Web Vitals, real long-form content explaining what each tool does and why. The goal is that someone searching "json formatter online" or "jwt decoder" lands on a useful page on the first try, not a slow ad-laden page that hijacks their clipboard.

How the tools are built

The site is built with Next.js (App Router) and Tailwind CSS. Each tool is a small React client island wrapped in a server-rendered page that ships its long-form explanation and SEO metadata. The interactive part downloads only when needed. There is no database, no backend service, no API that processes your input. Where a tool needs cryptography or hashing, it uses the browser's built-in Web Crypto API; where it needs random numbers for security, it uses crypto.getRandomValues with rejection sampling, never Math.random.

The full source is closed for now but the principles above are public. If you find a bug or want to suggest a tool, the contact link below is the best way to reach the maintainer.

What's next

Deftkit now spans 36 tools across eight categories — developer utilities, encoding/decoding, security, generators, converters, design, image, and PDF — with browsable category landing pages under /tools. Image and PDF work ship in-browser via the Canvas API, pdf-lib, and other WebAssembly modules, so even file-heavy tools stay fully client-side. The roadmap continues toward more converters and a few thoughtfully-chosen specialty tools. Content-style tools that need real backend processing (transcript extraction, longer-running jobs) will live on a separate subdomain so the core toolbox stays instant.

Privacy and ads

A complete description of what data is and isn't collected lives on the Privacy page. The short version: no data from any tool input is collected, ever. Standard anonymized page-visit analytics help us understand which tools are useful. When traffic justifies it, the site may display ads from Google AdSense to keep itself free; ads will be clearly marked and will never be inserted into a tool's input or output.

Contact

Bug reports, feature requests, suggestions for new tools, and general feedback are all welcome. The maintainer can be reached at hello@deftkit.com. Please include the tool name and what you were trying to do in any bug report so we can reproduce it locally. We don't promise a response time but every message is read by a human.

Credits

Built on the shoulders of many open-source projects, most notably:

• Next.js — the React framework that makes the instant-loading server-rendered pages possible
• Tailwind CSS — the styling system that keeps the UI consistent without a heavy component library
• React — the foundation of every interactive widget
• The Web Crypto API — built into your browser, the reason cryptographic tools can be both private and trustworthy
• pdf-lib — the WebAssembly-friendly PDF toolkit powering the PDF merge and split tools entirely in your browser
• qrcode — the QR generator library behind the Wi-Fi and URL codes
• js-yaml — the YAML parser that the YAML ⇄ JSON converter trusts to handle real-world anchors, multiline strings, and edge cases
• marked — the Markdown parser behind the live Markdown editor
• The EFF short wordlist (CC BY 3.0 US) — 1,296 memorable words with unique 3-character prefixes, the basis of the Diceware passphrase generator
• The 147-color CSS named-color list — public domain, makes the color converter useful
• Cicero, indirectly — the source of Lorem Ipsum, via a 16th-century printer who scrambled his text