Best use
Use it for a focused Run JS / HTML / CSS task when a quick browser workbench is appropriate.
HTML / CSS / JS Runner
Run small HTML, CSS, and JavaScript snippets in an isolated iframe sandbox with copy and reset actions.
Use cases and limits
Use this tool to preview small standalone snippets, demos, examples, or documentation code. The runtime uses an iframe sandbox and a restrictive CSP, so it is not equivalent to a full browser dev server.
Usage boundaries and result checks
Run JS / HTML / CSS is for this task: Run small HTML, CSS, and JavaScript snippets in an isolated iframe sandbox with copy and reset actions. It runs in the browser; start with a short, non-sensitive sample and confirm the behavior before processing more data.
Input
source code or markup snippets
Output
formatted text or a compact representation
Before reuse
For Run JS / HTML / CSS: Run the result through the target parser, linter, compiler, or test suite; readable formatting does not prove semantic correctness. See the test method.