nous-hermeshub Full Page Screenshot
Capture a full-page screenshot of any web page via Chrome DevTools Protocol. Produces a single PNG that includes all content — even portions that require scrolling. Zero external dependencies beyond Node.js 22+ and Chrome with remote debugging enabled.
Prerequisites
- Node.js 22+ (uses built-in
WebSocket) - Chrome/Chromium with remote debugging enabled
Check environment readiness:
node "${SKILL_DIR}/scripts/full-page-screenshot.mjs" --check
If Chrome check fails, instruct user to open chrome://inspect/#remote-debugging and enable "Allow remote debugging for this browser instance".
Workflow
Option A: Screenshot an already-open tab (recommended for authenticated pages)
- List available tabs:
node "${SKILL_DIR}/scripts/full-page-screenshot.mjs" --list
- Identify the target by title/URL, then capture:
node "${SKILL_DIR}/scripts/full-page-screenshot.mjs" <targetId> /tmp/screenshot.png --width 1200 --dpr 1
Option B: Screenshot a URL (opens a background tab, captures, closes)
node "${SKILL_DIR}/scripts/full-page-screenshot.mjs" --url "https://example.com" /tmp/screenshot.png --width 1200 --dpr 1 --wait 15000
Note:
--urlmode creates a background tab. Pages requiring authentication (SSO, login walls) should use Option A instead.
Parameters
| Parameter | Description | Default |
|---|---|---|
output |
Output PNG file path | /tmp/screenshot.png |
--width |
Viewport width in CSS pixels (articles: 1200, dashboards: 1440-1920) | 1200 |
--dpr |
Device pixel ratio (2 = Retina, but 4x file size) | 1 |
--wait |
Page load timeout in ms (--url mode only) |
15000 |
--css |
Custom CSS to inject before capture (e.g., hide elements) | — |
Verify Output
# macOS
sips -g pixelWidth -g pixelHeight /tmp/screenshot.png
# Linux
file /tmp/screenshot.png
Core Capabilities
SPA scroll container expansion — Detects
overflow-y: auto/scrollcontainers, scrolls through them to trigger lazy-loading, then removes overflow constraints (including Tailwindh-[calc(...)]) so all content renders in a single pass.DOM stability detection — After
readyState=complete, monitors DOM element count until it stabilizes. This ensures SPA frameworks finish rendering dynamic content.Lazy-load triggering — Scrolls the viewport incrementally to fire
IntersectionObservercallbacks, then waits for all<img>elements to complete loading.Tiled capture for very tall pages — Pages exceeding 16,000px are captured in 8,000px tiles and automatically stitched using Python PIL. Falls back to saving tiles separately if PIL is unavailable.
Auto-discovery of Chrome — Reads
DevToolsActivePortfile to find the debugging port. Falls back to probing ports 9222, 9229, 9333.CDP Proxy fallback — When a CDP proxy holds the browser WebSocket, the script falls back to proxy API endpoints (
/eval,/screenshot,/scroll) for capture.
How It Works
1. Discover Chrome debugging port
2. Connect via WebSocket (CDP)
3. Attach to target / create background tab
4. Set viewport width via Emulation domain
5. Wait: readyState + DOM stability
6. Detect & expand scroll containers
7. Scroll through page (trigger lazy-load)
8. Wait for images to complete
9. Measure final content height
10. Page.captureScreenshot (or tiled capture)
11. Stitch tiles if needed (PIL)
12. Restore viewport, detach, clean up
Anti-Patterns
| Do NOT | Do instead |
|---|---|
Use --dpr 2 on pages > 10,000px tall |
Use --dpr 1 to avoid Chrome memory issues |
Use --url for authenticated/SSO pages |
Use --list + targetId on a tab where user is logged in |
Set --wait below 5000 for SPAs |
SPAs need time to fetch data and render; use 10000-15000 |
Capture without checking --check first |
Always verify Chrome debugging is available |
| Hardcode viewport widths for all pages | Use 1200 for articles, 1440+ for dashboards/tables |
| Skip output verification | Always verify with sips or file command after capture |
Troubleshooting
| Symptom | Cause | Fix |
|---|---|---|
| "Cannot find Chrome debugging port" | Remote debugging not enabled | Open chrome://inspect/#remote-debugging, enable it |
| "WebSocket connection timeout" | CDP proxy holding the connection | Script auto-falls back to proxy API |
| Blank/white screenshot | Page not loaded yet | Increase --wait value |
| Truncated at bottom | Scroll container not expanded | Script handles this automatically; file an issue if it persists |
| Out of memory | Very tall page + high DPR | Reduce --dpr to 1 and/or reduce --width |
| "PIL not available for stitching" | Python Pillow not installed | Install with pip3 install Pillow or accept separate tile files |
Cross-References
engineering/browser-automation— General browser automation patterns via CDP/Playwrightengineering/performance-profiler— Performance analysis that may complement visual captures