ReSmush — Free Image Compression API (No Key)

TL;DR

ReSmush is a free image compression API that reduces PNG and JPEG file sizes using smart optimization algorithms. Upload an image URL or raw file data, and get back a compressed version with dramatically smaller file size while preserving visual quality. Supports JPEG (lossy compression) and PNG (lossless compression). Returns the compressed image with compression ratio statistics. JSON response includes original size, compressed size, and savings percentage. No API key. A must-have for web developers optimizing page load times.

Quick start: https://api.resmush.it/ws.php?img=https://example.com/image.jpg

No API key needed — just make a request!

How to Use This API

1. Compress an Image by URL

https://api.resmush.it/ws.php?img=https://example.com/image.jpg

2. JavaScript — Compress and Display

const imageUrl = 'https://upload.wikimedia.org/wikipedia/commons/4/47/PNG_transparency_demonstration_1.png';

fetch(`https://api.resmush.it/ws.php?img=${encodeURIComponent(imageUrl)}`)
  .then(r => r.json())
  .then(data => {
    console.log(`Original: ${data.src_size} bytes`);
    console.log(`Compressed: ${data.dest_size} bytes`);
    console.log(`Savings: ${data.percent}%`);
    console.log(`Result URL: ${data.dest}`);
  });

3. Python — Batch Compress Images

import requests

images = [
    'https://example.com/photo1.jpg',
    'https://example.com/photo2.jpg',
    'https://example.com/photo3.png',
]
for img_url in images:
    data = requests.get(
        'https://api.resmush.it/ws.php',
        params={'img': img_url}
    ).json()
    savings = data.get('percent', 0)
    print(f"{img_url.split('/')[-1]}: {savings}% reduction "
          f"({data.get('src_size', 0)} → {data.get('dest_size', 0)} bytes)")

Compress a test image: https://api.resmush.it/ws.php?img=https://example.com/image.jpg

Try This URL Now

Frequently Asked Questions

What image formats are supported?: JPEG (lossy compression) and PNG (lossless compression). The API auto-detects the format and applies appropriate optimization.
How much compression can I expect?: Typical savings range from 20-80% depending on image content. Photos with lots of detail compress less, while simple graphics and screenshots compress dramatically.
How do I upload a file directly?: Use a POST request with the files field containing the image data, or pass a publicly accessible URL with the img GET parameter.
What is returned in the response?: JSON with: dest (compressed image URL), src_size (original bytes), dest_size (compressed bytes), percent (savings percentage), and status code.
What is the maximum file size?: The free tier supports images up to 5MB. For larger images, consider resizing before compression or using a local Smush/ImageOptim tool.
Is there a rate limit?: ReSmush is a free public service with reasonable usage limits. For high-volume production use, consider self-hosting similar optimization tools.

API Details

API URL: https://api.resmush.it/ws.php
Documentation: resmush.it/api
Category: Developer Tools
Authentication: Not Required
Geographic Coverage: Global

What You Can Build

Image optimization pipeline for static site generators (Hugo, Jekyll, 11ty)
CMS plugin that auto-compresses uploaded images before storage
Batch image processor for web developers optimizing entire asset directories
CDN pre-processing service that compresses images on-the-fly
Performance audit tool measuring image compression opportunities on pages