How to Resize Images with curl (Free API, No Signup)

July 20, 2026 · Eric · 6 min read

Resizing images programmatically is one of those tasks that comes up constantly — whether you're building a thumbnail pipeline, optimizing images for a website, or processing uploads in a script. You could install ImageMagick, Sharp, or Pillow. But what if you just want one command that works everywhere?

The Agent Media Tools resize API lets you resize any publicly accessible image with a single curl call. No SDK. No signup. No API key. It handles JPEG, PNG, WebP, and AVIF, supports exact pixel dimensions and percentage scaling, and gives you control over output quality.

Here's every pattern you need — from a simple thumbnail downscale to advanced batch scripts.

The API at a Glance

The resize endpoint is a straightforward GET request:

GET https://agentmediatools.com/api/tool/resize-image?image_url={url}&width={w}&height={h}

You pass a public image URL, specify your target dimensions, and get the resized image back as the response body. That's it.

1. Exact Pixel Dimensions

Set width and height in pixels. The image is stretched to fit — use this when you know the exact canvas size you need.

curl "https://agentmediatools.com/api/tool/resize-image?image_url=https://example.com/photo.jpg&width=800&height=600" \
  --output resized.jpg

This downloads the image at 800×600 pixels, exactly.

💡 Tip

Supply both width and height if you need an exact fit. If you only supply one dimension, the other dimension scales proportionally — great for keeping aspect ratios.

2. Percentage Scaling

Instead of exact pixels, use percent to scale by a percentage of the original. This preserves the aspect ratio automatically.

# Scale to 50% of original size
curl "https://agentmediatools.com/api/tool/resize-image?image_url=https://example.com/photo.jpg&percent=50" \
  --output half-size.jpg

# Scale to 200% (enlarge)
curl "https://agentmediatools.com/api/tool/resize-image?image_url=https://example.com/photo.jpg&percent=200" \
  --output double-size.jpg

The percent parameter overrides width and height if set. Values below 100 shrink the image; values above 100 enlarge it.

⚠️ Note on Enlarging

Enlarging (upscaling) a raster image means the API must interpolate new pixels from existing ones. The result won't look as sharp as a native high-resolution original. For best quality, start from the largest source image you have and scale down.

3. Change the Output Format

Need a PNG instead of a JPEG? WebP for smaller file sizes? AVIF for next-gen compression? Pass a format parameter:

# JPEG → PNG
curl "https://agentmediatools.com/api/tool/resize-image?image_url=https://example.com/photo.jpg&width=400&height=400&format=png" \
  --output thumb.png

# JPEG → WebP (great for web performance)
curl "https://agentmediatools.com/api/tool/resize-image?image_url=https://example.com/photo.jpg&width=1200&format=webp" \
  --output hero.webp

# JPEG → AVIF (even better compression)
curl "https://agentmediatools.com/api/tool/resize-image?image_url=https://example.com/photo.jpg&width=800&format=avif" \
  --output compressed.avif

Supported output formats: jpeg, png, webp, avif.

4. Quality Control

Lossy formats (JPEG, WebP, AVIF) let you trade file size for quality with a quality parameter from 1 (smallest, worst) to 100 (largest, best). The default is 80.

# High-quality JPEG at 95
curl "https://agentmediatools.com/api/tool/resize-image?image_url=https://example.com/photo.jpg&width=1920&quality=95" \
  --output high-quality.jpg

# Aggressive compression at 30 (tiny file, visible artifacts)
curl "https://agentmediatools.com/api/tool/resize-image?image_url=https://example.com/photo.jpg&width=1920&quality=30" \
  --output tiny.jpg

5. Real-World Use Cases

Download all images from a page at a consistent size

# Grab an image, resize it to a 300px square thumbnail
for url in \
  "https://site.com/img1.jpg" \
  "https://site.com/img2.jpg" \
  "https://site.com/img3.jpg"; do
  filename=$(basename "$url")
  curl -s "https://agentmediatools.com/api/tool/resize-image?image_url=$url&width=300&height=300" \
    --output "thumb-$filename"
done

Generate responsive image variants for a web page

SOURCE="https://images.example.com/hero.jpg"

# Desktop: 1920px wide, WebP, quality 85
curl -s "https://agentmediatools.com/api/tool/resize-image?image_url=$SOURCE&width=1920&format=webp&quality=85" \
  --output hero-desktop.webp

# Tablet: 1024px wide, WebP, quality 80
curl -s "https://agentmediatools.com/api/tool/resize-image?image_url=$SOURCE&width=1024&format=webp&quality=80" \
  --output hero-tablet.webp

# Mobile: 480px wide, WebP, quality 75
curl -s "https://agentmediatools.com/api/tool/resize-image?image_url=$SOURCE&width=480&format=webp&quality=75" \
  --output hero-mobile.webp

Batch-resize an entire directory (with Python)

#!/usr/bin/env python3
"""Upload all images in a directory to a public URL, then resize them."""
import subprocess, sys, glob

for path in glob.glob("images/*.jpg"):
    # Option A: upload to a public host, then call the API
    # Option B: use the Agent Media Tools pipeline (see below)

    # If the image is already online:
    url = f"https://example.com/uploads/{path.split('/')[-1]}"
    out = f"resized/{path.split('/')[-1]}"
    subprocess.run([
        "curl", "-s",
        f"https://agentmediatools.com/api/tool/resize-image",
        "--data-urlencode", f"image_url={url}",
        "--data-urlencode", "width=640",
        "-o", out
    ])

6. Using the API from AI Agents (MCP)

If you run Claude, Cursor, or any MCP-compatible agent, you can connect the resize tool directly into your agent's toolbox. Set up the MCP server with your API key, and your agent can resize images on the fly — no curl needed.

The MCP server exposes the resize tool as resize_image. Your agent will automatically handle fetching the image, applying the resize, and saving the result. It's the same underlying API — just accessed through the agent's natural language interface.

Check the MCP setup guide for step-by-step instructions.

7. Combine with Other Tools

The resize API works great in pipelines with other tools. Here are a few common chains:

Resize → Compress: First resize to your target dimensions, then pass the result through the compress API to shrink file size further.
Resize → Convert → Watermark: Resize, convert to WebP, then add a watermark. The tools all consume public URLs, so you can chain them with simple curl pipes.
Screenshot → Resize → Store: Take a full-page screenshot with the screenshot API, resize it to a thumbnail, and store the result as an artifact.

Ready to try it? You don't need an account. Run any of the curl commands above — they work immediately.

For higher volumes, format conversion, and MCP agent integration, grab a free API key.

Get Started →

API Reference Summary

Parameter	Type	Description
`image_url`	string	Public URL of the source image (required)
`width`	integer	Target width in pixels
`height`	integer	Target height in pixels
`percent`	integer	Scale by percentage (overrides width/height)
`format`	string	Output format: jpeg, png, webp, avif (default: source format)
`quality`	integer	1–100 (default 80). Lower = smaller file.

The base URL is https://agentmediatools.com/api/tool/resize-image. No authentication is required for basic use.

Why Use an API Instead of a Local Library?

If you have ImageMagick or Sharp installed, you can resize locally. But the API approach wins in several scenarios:

Ephemeral environments: Serverless functions, CI runners, and sandboxed agents often can't install native image libraries. A curl call works everywhere.
No storage overhead: The API fetches the image from a URL and returns the result — you never need to download the original first or clean up temp files.
Format conversion built in: Converting between JPEG, PNG, WebP, and AVIF is a single parameter, not a multi-step toolchain.
AI agent integration: Every MCP-compatible agent (Claude, Cursor, Continue, etc.) can call this API as a native tool — no plugin code to write.

Give it a try. Open your terminal and run one of the commands above. You'll have a resized image in about a second.

— Eric, building Agent Media Tools