inspecting-hermes-desktop-dom

Connect to the Chrome DevTools Protocol port the dev server opens on 127.0.0.1:9222, then evaluate JavaScript against the renderer page. In this repo, run node scripts/eval.mjs with your expression from apps/desktop, or use the shared CDP client for multi-step queries.

Query the real rendered node over CDP and read its className, getComputedStyle value, and ancestor class chain. If the node carries no class of its own, the value is inherited, so fix the ancestor or shared-class rule rather than sweeping call sites.

The port is closed for packaged builds and for unpackaged runs without HERMES_DESKTOP_DEV_SERVER. Check with curl against /json/version first, and never relaunch the user's app — start an isolated instance with HERMES_DESKTOP_CDP_PORT set to a different port instead.

Yes. Launch your own Electron instance with a throwaway HERMES_HOME, a separate --user-data-dir to dodge the single-instance lock, and a non-default CDP port such as 9333. The renderer still mounts and the DOM stays readable even without a backend.

CDP answers factual questions like computed padding or whether an element rendered, but cannot judge aesthetics such as color balance or spacing feel. It also does not cover perf profiling or heap work, which belong to dedicated debugging skills.