Using REA to Trace How Codex Attaches Browser Annotations

What happened

Baoyu describes using the open-source REA (Reverse Engineer Anything) MCP service to understand how Codex and the ChatGPT app attach browser annotations to the composer, without decompiling Codex itself. After REA traced the Electron app's code path, Codex built a test page that could open a comment box and prefill input via document.oai.annotation.request(), an OpenAI API the author had not known about. Cursor and Claude Code did not support a similar API.

The story so far

Baoyu (@dotey) said he used the open-source REA (Reverse Engineer Anything) MCP service to trace how Codex and the ChatGPT app attach browser annotations to the composer, without decompiling Codex itself. After REA traced the Electron app's code path, he had Codex build a test page that could open a comment box and prefill input via document.oai.annotation.request(), an OpenAI API he said he had not previously known about. The test page did not attach comments directly to the input box; it could pop up a comment box and fill in the input content, according to Baoyu. He added that Cursor and Claude Code do not support a similar API.

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