I Built a File Converter That Handles 16 Formats in the Browser — No Upload Required

A client once sent me a PDF invoice and asked for it as a CSV. Then sent a HEIC photo that needed to be PNG. Then an XML config that needed JSON. Three different tools, three different uploads, three different privacy policies to read.

I got fed up and built one tool that handles all of it locally.

The Stack

The core is surprisingly simple. Each conversion is an "engine" — a small JavaScript module that takes input and returns output:

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  PDF to JPG: Canvas-based page rendering + per-page export


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  HEIC to PNG: heic2any library, all client-side decoding


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  JSON ↔ CSV: PapaParse for CSV, native JSON.stringify/parse


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  XML ↔ JSON: DOMParser for XML parsing, zero dependencies


• 
  SVG to PNG: Canvas drawImage with crossOrigin handling


• 
  Markdown to HTML: marked.js, 2KB minified

16 engines total, all running in the browser at for vector graphics

All of them share the same principle: files stay in browser memory. Open DevTools Network tab while using any of them — zero uploads.

Building browser-local tools taught me that we've normalized sending files to strangers' servers for things our own computers can do faster.