The developer toolbox that
never phones home.
100+ free, browser-based developer tools for JSON, encoding, hashing, CSS, code formatting, and more. Every tool runs entirely on your device. No login. No tracking. No uploads.
Why Catalyst exists
Most online developer tools have a problem you can't see: they receive your data. Paste a JSON payload into a random formatter and you have no way to know whether it was logged, cached, indexed, or sold. For personal projects this is merely uncomfortable. For production API responses, customer data, or internal config files, it is a compliance incident waiting to happen.
Catalyst was built on a simple premise: every one of these tools can run entirely in the browser using native JavaScript and Web APIs. JSON parsing, Base64 encoding, SHA-256 hashing, AES encryption, regex matching, image resizing — all of it works without a server round-trip. So that's what we built. Every tool here is a single HTML page that never transmits your input anywhere.
The result is a developer toolbox you can trust with real data: production API payloads, JWTs pulled from incident logs, AES-encrypted config values, customer PII during debugging. Everything stays on your machine.
What we believe
Privacy by default
Every tool runs 100% in your browser via native JavaScript and Web APIs. Your data — JSON payloads, JWTs, passwords, source code, images — never touches any server, is never logged, and is never cached. You can verify this by disconnecting your network and watching the tools continue to work.
Instant, no friction
No signup. No login. No API key. No rate limits. Just paste, process, and copy. Every page is a standalone static HTML document, so load times stay under a second even on slow connections.
Safe for confidential data
Because nothing leaves your device, these tools are safe to use with production API responses, internal config files, customer data, and proprietary source code that would normally require an air-gapped environment.
Built by developers, for developers
Every tool addresses a real task we run into ourselves: debugging a malformed API response at 2am, verifying a webhook signature, generating a UUID in a script, formatting a complex SQL query. The toolset is opinionated and practical, not a feature checklist.
Free, forever
Catalyst is funded by non-intrusive display ads and will remain free for all users. There is no paid tier, no enterprise license, no "unlock premium features" prompt. Close the ads if you prefer; everything works the same.
12 toolkits, 100+ tools
Tools are organized into 12 category toolkits. Each toolkit includes a tabbed interface for its sub-tools, and each sub-tool has its own dedicated URL for direct linking.
How it works under the hood
Catalyst is a Next.js application built with the App Router and statically generated. Every tool page is a pre-rendered HTML file served from a CDN, with a small JavaScript bundle that hydrates the interactive tool on your device.
Cryptographic tools (hashing, HMAC, AES encryption, JWT signing) use the browser's native crypto.subtle API — the same implementation that powers TLS and WebAuthn. Random values come from crypto.getRandomValues(), a CSPRNG. JSON, YAML, XML, and Markdown parsers run as pure JavaScript libraries bundled into the page.
The one exception is the IP Address Info tool, which fetches your public IP and geolocation from a public API because that data is not available from within the browser alone. Every other tool is fully offline-capable after the initial page load.
Get in touch
Feedback, bug reports, and tool requests are welcome. Catalyst is a solo project built in the open, and every suggestion helps improve the toolset for everyone.