snapshot

Capture and compare visual snapshots for regression testing. Take a baseline set of screenshots, make changes, then compare — snapshot computes per-page pixel diffs and flags regressions against a threshold.

Synopsis

snapshot {action: "screenshot", proxy_id: "dev"}
snapshot {action: "baseline", name: "before-refactor", pages: [...]}
snapshot {action: "compare", baseline: "before-refactor", pages: [...]}
snapshot {action: "list"}

Actions

Action	Description
screenshot	Capture the current page of a running proxy (writes a PNG, returns the path)
baseline	Create a named baseline from a set of screenshots
compare	Compare current screenshots against a baseline and report diffs
list	List all available baselines
get	Get details of a specific baseline
delete	Delete a baseline

Parameters

Parameter	Type	Used by	Description
action	string	all	One of the actions above
name	string	baseline / compare / delete / get; optional for screenshot	Baseline or screenshot name
baseline	string	compare	Baseline name to compare against
pages	array	baseline / compare	Pages to capture: [{url, viewport, screenshot_data}]
diff_threshold	float	compare	Diff sensitivity 0.0–1.0 (default 0.01)
proxy_id	string	screenshot	Proxy whose current page to capture (preferred)
id	string	screenshot	Alias for proxy_id
selector	string	screenshot	CSS selector to capture (default: full viewport)
full_page	bool	screenshot	Capture the full scrollable page (default: viewport only)

Capturing a Screenshot

snapshot {action: "screenshot", proxy_id: "dev"}
snapshot {action: "screenshot", proxy_id: "dev", name: "homepage", full_page: true}
snapshot {action: "screenshot", proxy_id: "dev", selector: ".header"}

The screenshot action requires daemon mode (it routes through the daemon's proxy session). It writes a PNG and returns its path.

Baseline / Compare Workflow

// 1. Capture a baseline before changes
snapshot {action: "baseline", name: "before-refactor",
  pages: [{url: "/", viewport: {width: 1920, height: 1080}, screenshot_data: "base64..."}]}

// 2. After changes, compare
snapshot {action: "compare", baseline: "before-refactor",
  pages: [{url: "/", viewport: {width: 1920, height: 1080}, screenshot_data: "base64..."}]}

Comparison reports per-page diff_percentage, a saved diff-image path, and a summary:

{
  "baseline_name": "before-refactor",
  "pages": [
    {"url": "/", "diff_percentage": 2.5, "has_changes": true, "diff_image_path": "...", "description": "Moderate changes (2.50%)"}
  ],
  "summary": {"total_pages": 1, "pages_changed": 1, "average_diff": 2.5, "has_regressions": true}
}

A page counts as changed when its diff exceeds diff_threshold.

See Also

• responsive_audit — viewport-size regression checks
• Visual Regression Testing with AI — workflow guide
• proxy — proxy lifecycle the screenshot action drives