How I Built a Pure Client-Side Image Compressor (No Server, No API)

entry bypass — Sat, 13 Dec 2025 15:20:04 +0000

Most image compression tools upload your photos to a server. That’s fine for casual images, but not okay when users are working with personal documents like Aadhaar cards, PAN cards, or government exam forms.

I ran into this issue myself while helping someone upload a photo with a strict 20KB file size limit. Most tools either broke the quality or failed to hit the exact size. So I decided to build my own tool that works 100% inside the browser — no backend, no APIs, no uploads.

That’s how ResizeKB.tech was born.

PROBLEM I WANTED TO SOLVE

Government and job application portals in India often require:

Exact file size limits (20KB, 50KB, 100KB)
Specific dimensions
Clean background images
No quality loss

Most tools:

Upload images to a server
Compress blindly
Don’t allow exact KB targeting
Create privacy issues

My goal was:

Exact size control
No server
No upload
Works instantly

TECH STACK

HTML5
Vanilla JavaScript
HTML Canvas API
Browser File API

HOW IT WORKS

User selects an image
Image loads using FileReader
It is drawn onto a hidden canvas
Quality + resolution are adjusted
Export happens using canvas.toBlob()
Loop runs until exact KB size is reached

Everything happens locally. No file is uploaded anywhere.

BIGGEST CHALLENGES

Maintaining quality under 20KB
Handling large phone images
Browser memory crashes
Different compression results in different browsers

PRIVACY

No login
No uploads
No server
No tracking

LIVE TOOL

https://resizekb.tech

You can check the browser Network tab — there is zero upload.

FINAL NOTE

This started as a personal fix for government form uploads and slowly became a daily-use tool for thousands of users.

If you're building browser-based tools or care about privacy-first apps, happy to connect.

DEV Community: entry bypass

How I Built a Pure Client-Side Image Compressor (No Server, No API)