Source inspection cannot prove a rendered interface works. Codex can operate the UI, reproduce the failure, change the code, and repeat the same flow.
| Target | Use |
|---|---|
| Local or public page without sign-in | In-app Browser |
| Signed-in Chrome state or extensions | Chrome integration |
| Native desktop application | Computer Use |
| Structured external system | Dedicated plugin or MCP first |
Open http://localhost:3000/settings.
At 390px width, reproduce the overflowing Save button.
Fix only the layout cause.
Repeat the same flow and capture the verified state.Pages and desktop apps can contain misleading instructions. Keep sensitive apps closed, scope the target, and review signed-in or state-changing actions.
A screenshot proves appearance at one moment. Strong UI verification combines several kinds of evidence:
| Evidence | What it proves |
|---|---|
| Exact interaction sequence | The state is reproducible |
| DOM and computed styles | The rendered structure and layout cause |
| Console output | Client-side failures and warnings |
| Network trace | Requests, timing, status, and payload shape |
| Before-and-after screenshot | The visible outcome changed as intended |
Responsive success at one width does not cover loading, empty, error, keyboard, or long-content states. Select only the states relevant to the change, but name them explicitly.
Reproduce → capture evidence → make one scoped change → repeat the identical flow → inspect the diff. Changing the reproduction halfway through weakens the result.
Pick one local route and define a three-step reproduction with an exact viewport, data state, and observable pass condition. Specify which screenshot, console, DOM, or network evidence Codex must return after repeating the flow.