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compress-images

Skill30 starsChanged 9 months agoMITView on GitHub

Compress images for web/SEO performance using cwebp. Use when optimizing images for faster page loads, reducing file sizes, or converting JPG/PNG to WebP format.

The file

We split this skill into the rules it gives an agent

5 rules. About 0 are common, 4 are distinctive, and 1 is very specific to this project.

  • ≈0

    Common · estimate

    Many files like this have a rule of this kind.

  • ≈4

    Distinctive · estimate

    This author's own choices. Worth a look.

  • 1

    Very specific

    Tied to their project's names, files or tools. Probably skip.

  • Common
  • Distinctive
  • Very specific
  1. Very specific:

    Create originals folder: - Create originals/ subfolder inside the target directory and move source files there.

    line 14
  2. Distinctive:

    Iterate until all images are under 100KB: - check sizes after each pass, re-compress any that exceed the target

    line 16
  3. Distinctive:

    IMPORTANT: Keep compressing until ALL images are under 100KB.

    line 33
  4. Distinctive:

    Update content files referencing old extensions (.jpg, .png) to use .webp

    line 85
  5. Distinctive:

    Test that images render correctly in the application

    line 86

≈ “Common” is an estimate: at least 1 in 5 of the 350,495 skill files we read have a rule of the same kind, not the same words. “Very specific” is our guess from the words: it names a file, a command, a setting or the project itself.

Keep what fits and drop the rest. Your version, ready for your agents.
Files
SKILL.md

Image Compression Skill

Compress all images in $ARGUMENTS (or app/assets/images/content/ if no path provided) to WebP format, optimized for SEO performance (target: under 100KB per image).

Process

  1. Create originals folder - Create originals/ subfolder inside the target directory and move source files there. Never destroy source files.
  2. Compress each image (JPG, PNG, GIF) from originals/ to the parent directory as .webp
  3. Iterate until all images are under 100KB - check sizes after each pass, re-compress any that exceed the target
  4. Report results with before/after sizes
  5. Update references in content files from old extensions to .webp

File Structure

target-directory/
├── originals/           # High-quality source files preserved here
│   ├── hero.jpg
│   └── feature.png
├── hero.webp            # Compressed, web-optimized
└── feature.webp

Iterative Compression Algorithm

IMPORTANT: Keep compressing until ALL images are under 100KB. Check sizes after each pass and re-compress any that exceed the target.

Step 1: Initial pass (q 70)

cwebp -q 70 -resize 1200 0 originals/image.jpg -o image.webp
ls -lh image.webp  # Check size

Step 2: If still over 100KB, reduce quality progressively

# Try these in order until under 100KB:
cwebp -q 60 -resize 1200 0 originals/image.jpg -o image.webp
cwebp -q 50 -resize 1200 0 originals/image.jpg -o image.webp
cwebp -q 45 -resize 1200 0 originals/image.jpg -o image.webp
cwebp -q 40 -resize 1200 0 originals/image.jpg -o image.webp
cwebp -q 35 -resize 1200 0 originals/image.jpg -o image.webp

Step 3: For stubborn images, also reduce dimensions

# If q 35 at 1200px is still over 100KB, reduce to 1000px:
cwebp -q 30 -resize 1000 0 originals/image.jpg -o image.webp
cwebp -q 25 -resize 1000 0 originals/image.jpg -o image.webp

Real-World Results (Reference)

From actual compression run on content images:

ImageOriginalFirst TryFinalSettings Used
waves.jpg198KB33KB33KBq 70, 1200px (1 pass)
calendar.jpg246KB42KB42KBq 70, 1200px (1 pass)
floating.jpg230KB43KB43KBq 70, 1200px (1 pass)
cash.jpg409KB88KB88KBq 70, 1200px (1 pass)
knot.jpg395KB96KB96KBq 70, 1200px (1 pass)
floating-dark.jpg414KB94KB94KBq 70, 1200px (1 pass)
keyboard2.jpg459KB102KB102KBq 70, 1200px (1 pass, acceptable)
perpetual.jpg565KB130KB96KBq 40, 1200px (3 passes)
keyboard.jpg718KB196KB98KBq 25, 1000px (5 passes)

Key Insights

  1. Most images (under 500KB source) compress fine with default settings (q 70, 1200px)
  2. Large detailed images (500KB+) often need multiple passes
  3. Very large images (700KB+) may need both lower quality AND smaller dimensions
  4. Keyboard/tech photos with fine detail are hardest to compress - expect 4-5 passes
  5. Soft/blurry images compress much better than sharp detailed ones

After Compression

  1. Verify ALL files under 100KB: ls -lh *.webp - re-run compression on any exceeding target
  2. Update content files referencing old extensions (.jpg, .png) to use .webp
  3. Test that images render correctly in the application
  4. Original files remain in originals/ folder for future reference or re-compression

Download now (ZIP)

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