How I built a Serverless PDF Editor with Vanilla JS (and $0 cloud bills)

Remolinator — Sat, 20 Dec 2025 20:31:25 +0000

We all have that moment. You need to merge two PDF contracts or compress a video file, and you search on Google. You find a tool, upload your file, and then... you wait.

And then you wonder: "Wait, did I just upload my tax return to a random server in a country I can't pronounce?"

That paranoia is exactly why I built DuneTools.

I wanted to challenge the status quo of heavy, server-dependent web apps. My goal was simple: build a suite of tools (PDF, Video, Image) that runs 100% in the browser. No uploads. No privacy risks. Just pure JavaScript.

Here is how I built it (and why I ditched React for this one).

1. The Architecture: Client-Side is King 👑

Most PDF tools work like this:
User -> Upload -> Server processes (Python/PHP) -> Download

DuneTools works like this:
User -> Browser (WASM + JS) processes -> Done

By using libraries like pdf-lib and WebAssembly wrappers for FFMPEG, modern browsers are powerful enough to handle heavy media editing. This has two massive benefits:

Privacy: The file never leaves the user's device.
Cost: My server costs are flat. Whether I have 10 users or 10,000, I don't pay for CPU processing time.

2. Why Vanilla JS? (No React, No Vue) 🍦

I know, I know. It's 2025. Why aren't you using Next.js?

For a tool like this, performance is the feature. I didn't want to ship 200KB of hydration scripts just to render a "Merge PDF" button.

My "Hybrid" Build Workflow

Instead of a heavy JS framework, I use Python as a static site generator:

I write my logic in plain Vanilla JS.
I use Python + Jinja2 templates to generate the HTML pages for each tool (SEO is crucial here).
The Python script compiles everything into a static folder ready for deployment.

The result?

Lighthouse Score: 100/100 🟢
Load Time: Instant.

3. The Deployment: Vercel (Zero Config) ▲

Since this is a client-side app with no backend database, I didn't want to manage servers, SSH keys, or Docker containers.

I chose Vercel for deployment. It fits perfectly with my "lazy developer" philosophy:

Git Integration: I push my generated static files to GitHub, and Vercel detects the change and deploys automatically.
Global CDN: My static assets (JS/WASM) are cached on the edge, making the tool load instantly from anywhere in the world.
Cost: Free. Since I'm not using Serverless Functions for processing (remember, it's all client-side), I stay comfortably within the free tier limits.

It’s the ultimate "set it and forget it" setup.

4. The Result: DuneTools 🏜️

The project is now live. It includes:

PDF Tools: Merge, Split, Compress.
Video: Converter, GIF maker.
Images: Compression, resizing.

It’s fast, it’s free, and most importantly, it’s private.

I'd love for you to roast my code or give me feedback on the UX.

👉 Try it here: DuneTools.com