T3 preview

Direct HTML preview (default)

For static pages and interactive mocks with no backend, write an HTML file and link its absolute path in the reply, for example [Open the page](/tmp/demo/index.html).

T3's file panel renders HTML and runs its scripts over the existing connection, including remote connections. No server or separate tunnel is needed. Files inside the workspace can load sibling assets. For files outside the workspace, keep every asset inline.

The preview_* tools drive the browser tab, not the file panel.

Server previews

For a backend, dev server, or browser automation, follow server previews.

For either route, report unverified visual, interaction, or backend checks and link the preview cleanup record.

Viewport and theme checks

Use preview_resize and preview_set_appearance on the browser route. Without that route, install Playwright outside the project lockfile and use its viewport, isMobile, and colorScheme options. Headless Chrome's --window-size does not narrow the layout below about 500px.

Each preview screenshot also returns the page's accessibility tree and logs. Capture large screenshot sets with Playwright, and use the preview browser for interaction and spot checks.

Set each prefers-color-scheme value before load, or reload after changing it, because scripts and canvas scenes often read it once. If the product sets its theme with a class or stored setting, switch it through the product's own toggle. Before trusting a canvas screenshot, confirm that the headless browser created a WebGL context. If it did not, relaunch with software GL (--use-angle=swiftshader --enable-unsafe-swiftshader) or run headed.