Last month I needed to redact a bank statement PDF and convert a couple of voice memos to MP3.
I did what everyone else does: searched Google, clicked the first result, and uploaded my file. Right after hitting upload, two things annoyed me:
- I had just handed a document containing my home address and account number to a random third-party server.
- When I tried to process a second file, I got hit with a "Free daily limit reached — Upgrade to Pro for $12/month" paywall.
As developers, we know modern browsers are basically full operating systems. Between WebAssembly, the Web Audio API, OffscreenCanvas, and ArrayBuffer streams, there is zero technical reason a browser needs to upload a 5MB PDF or an MP3 file to a cloud server just to split pages or trim audio.
So I started building my own local-first utility belt. What began as a weekend project turned into Super ToolKit — a collection of 100+ tools that run 100% inside the browser tab.
What’s inside right now?
Instead of making you bounce between ten different ad-heavy sites, everything lives in one clean workspace with zero sign-ups:
1. Audio & DSP Studio (Powered by Web Audio API)
- Vocal Remover & Karaoke Isolator: Uses mid-side phase cancellation and spectral filtering directly in your browser to strip vocals or isolate acapella tracks in real time.
- Audio Reverb Studio: Impulse-response convolution reverb + lush slowdown effects without opening a heavy DAW.
- 8D Spatial Audio Panner & Dolby-Style Enhancer: Real-time binaural panning and multi-band compression.
- Video to Audio Extractor & BPM / Key Detector.
2. Private PDF & Document Tools (Zero Cloud Uploads)
- PDF Merger, Splitter, & Redactor: Merge, slice, or permanently black out sensitive text locally in RAM.
- Password Protect / Unlock PDF & Digital PDF Signer.
- Remove PDF Metadata: Strip hidden author names and creation timestamps before sharing files.
3. Daily Developer Utilities
- JSON to TypeScript / Cleaner & SQL Formatter.
- JWT Debugger (verify tokens without pasting production secrets into external logs).
- cURL to Code Converter, Regex Studio, Cron Builder, and Chmod Calculator.
4. Image & Data Conversion
How it works under the hood
- No file storage: Your files never leave your device. If you load a tool and turn off your Wi-Fi, it still works because the processing happens on your own CPU/GPU.
- PWA & Offline support: You can install it as a desktop or mobile app, or grab the Chrome Extension for one-click access.
- No accounts or paywalls: No "sign in with Google to download your file" traps.
Try it out & let me know what’s missing
You can test the live app here:
👉 https://supertoolkit.app/
GitHub Org: github.com/supertoolkit-app
I’m actively adding new utilities every week. What is that one annoying micro-task you still find yourself Googling a random website for? Drop it in the comments and I’ll build it into the next release!
Top comments (1)
Hey DEV community! 👋
Quick question for everyone here: when you're working locally, which browser-based utility do you reach for the most JSON/JWT debugging, quick image compression, or PDF tweaks?
If you run into any bugs or have a specific format converter you want added, reply here and I'll ship it this week!