SKILL.md
1. Role
Use screenshot-diff as supporting visual evidence for UI QA and visual regression checks. It highlights pixel-visible change or stability; it does not replace visual inspection, accessibility/component-tree state, frame/attribute checks, logs, network evidence, or app behavior.
Do not use screenshot diffing for tap-coordinate discovery. Use describe, debugger-component-tree, or native-describe-screen to find targets first.
screenshot-diff supports physical iPhones (kind "device") for both saved-file diffs and live captures. A live capture on hardware goes through the on-device runner at full resolution, is device-wide, and needs no registered app. Keep baselines per device model and resolution, and note that the rotation parameter is ignored on hardware: the capture follows the device's real orientation.
2. When To Use
Use screenshot-diff when pixel comparison can answer the verification question:
- Required for explicit "UI regression test", "visual regression test", "screenshot diff", "compare screenshots", or "before/after visual comparison" requests, unless stable comparable screenshots cannot be produced.
- Good fit when the affected screen has stable before/after states and the expected result is pixel-visible: layout, position, size, spacing, color, typography, image/icon rendering, clipping, overflow, or text rendering.
- Good fit when the risk is unintended visual regression outside the exact element changed.
- Poor fit when the result is better verified structurally: state changes, navigation existence, accessibility tree contents, console/network behavior, or unit tests.
- Poor fit when dynamic content, unpausable animation, timestamps, ads, random data, or missing baseline/current screenshots would make the comparison noisy or meaningless.