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screenshot-validation

This skill validates screenshot images and viewer HTML files used as PR evidence by checking image dimensions (minimum 400x400 pixels), viewport width (1280 pixels recommended), file size (under 5MB), blankness detection, and rendering correctness using headless Chromium. Use it after adding or modifying images in the evidence directories or generating new viewer HTML files to ensure quality standards are met before committing to prevent CI failures.

View source Repository: claude-tap

Install in Claude Code

Copy

git clone --depth 1 https://github.com/liaohch3/claude-tap /tmp/screenshot-validation && cp -r /tmp/screenshot-validation/.agents/skills/screenshot-validation ~/.claude/skills/screenshot-validation

Then start a new Claude Code session; the skill loads automatically.

Definition

SKILL.md

# Screenshot Validation

Validate that evidence images and viewer HTML files meet quality standards before committing. This catches issues that would otherwise fail CI or produce misleading PR evidence.

## Image quality check

Checks PNG/JPG/GIF/WEBP files for:
- **Minimum dimensions**: 400x400 pixels (hard fail)
- **Desktop viewport width**: >= 1280px (warning if narrower)
- **File size**: <= 5MB (warning if larger)
- **Blankness detection** (PNG only): fails if > 90% of pixels are white/transparent

### Run on specific files or directories

```bash
uv run python scripts/check_screenshots.py .agents/evidence/pr/
uv run python scripts/check_screenshots.py .agents/recordings/
uv run python scripts/check_screenshots.py path/to/specific-image.png
```

### Run on git-staged images

```bash
scripts/check_screenshots.sh
```

This shell wrapper automatically finds staged PNG/JPG files and runs the quality check on them — useful as a pre-commit sanity check.

## Viewer HTML rendering verification

Uses Playwright (headless Chromium) to verify that generated viewer HTML files actually render correctly — not just raw JSON or Python errors.

Checks:
- No JavaScript errors on page load
- Normal traces render a sidebar with entries and a detail panel
- Empty embedded traces render the explicit "No API calls captured" state
- Body text doesn't contain raw JSON dumps or Python tracebacks

### Run

```bash
uv run python scripts/verify_screenshots.py .traces/trace_*.html
```

Requires Playwright to be installed (`uv pip install playwright && playwright install chromium`).

## Typical workflow

After generating new evidence for a PR:

```bash
# 1. Check image quality
uv run python scripts/check_screenshots.py .agents/evidence/pr/

# 2. If you generated new viewer HTML, verify it renders
uv run python scripts/verify_screenshots.py .traces/trace_*.html

# 3. If all passes, stage and commit
git add .agents/evidence/pr/
```

## Fixing common failures

| Failure | Fix |
|---------|-----|
| `very small image (WxH; minimum is 400x400)` | Retake screenshot at a larger viewport or higher resolution |
| `narrow desktop viewport (Wpx < 1280px)` | Resize browser window to >= 1280px wide before capturing |
| `mostly blank/white image` | Ensure the screenshot captures actual content, not an empty page |
| `No sidebar — viewer not rendered` | Viewer HTML is broken; regenerate from trace JSONL |
| `JS errors` | Check viewer.html for syntax errors in embedded data |