I built an in-browser Swiss Army Knife with zero server uploads (PDFs, Images, JWT, Hashes)

Isaac Kojo Yankson — Tue, 22 Sep 2026 21:25:47 +0000

Every day, developers and power users need quick micro-tasks done:

Formatting or minifying a raw JSON response
Inspecting a JWT header & checking expiration timestamps
Stripping GPS coordinates and EXIF metadata from an image
Converting a WebP/HEIC image to PNG
Merging two PDF pages or rotating a document

The problem? Most popular tools force you to upload sensitive company data, contracts, or auth tokens to third-party cloud servers. Plus, they hit you with daily limits or $15/month subscriptions.

I built Convertum to solve this by bringing all processing 100% into the browser memory sandbox.

🛡️ Why Zero-Upload Matters

When you paste an auth token into an online JWT inspector or upload an invoice to a cloud PDF merger, you're trusting an unknown backend with confidential data.

With modern browser capabilities (WebAssembly, HTML5 Canvas, and Web Crypto), there is no reason simple transformations need a backend server:

Zero Data Retention: Calculations happen locally in browser RAM. No files leave your machine.
Instant Speed: No upload wait, no queueing, and no server latency.
No File Size Limits: You aren't constrained by server upload quotas.

🛠️ What's Inside the Toolbox

1. Developer & Security Studio

JWT Inspector: Decodes headers and payloads client-side, validating exp timestamps and signature formats without network requests.
JSON & CSV Studio: In-browser JSON formatter, schema validator, minifier, and 1-click JSON-to-CSV converter.
Cryptographic Hashes: Instant SHA-256 and SHA-512 calculation via the native crypto.subtle API, UTF-8 safe Base64 encoder, and URL decoders.
UUID & Strong Passwords: Cryptographically secure RFC-compliant UUID v4 generator.

2. PDF & Media Studio

PDF Manipulation: Merge, split, rotate, and re-order PDF pages locally using in-memory WebAssembly.
Image Converter & Compressor: Canvas-based WebP, PNG, and JPEG conversion with visual quality sliders and automatic EXIF/GPS stripping.
Specialized Formats: Client-side Apple HEIC to PNG conversion, Korean HWP document viewer, and universal e-invoice parsers (Factur-X, XRechnung).

3. Chrome Side Panel Integration

You can dock the entire studio into Chrome's native Side Panel (Alt + Shift + C) to inspect API payloads, generate test data, or format text side-by-side without leaving your active tab.

💻 Tech Stack

Framework: React + TypeScript + Vite
Processing Engines: HTML5 Canvas API, Web Crypto API, WebAssembly
Extension: Chrome Manifest V3 (Side Panel API & Context Menus)

🔗 Try It Out

Check out the live web app and extension:
👉 Convertum Web App (convertum.app)

I'd love to hear your feedback:

What micro-tools do you find yourself reaching for during daily development?
Any specific formats or utilities you'd like to see added?

DEV Community: Isaac Kojo Yankson