--- schema: 1 type: video title: 'Why MCP and ChatGPT Apps Use Double Iframes — Frédéric Barthelet, Alpic' description: >- Inspect ChatGPT's DOM while an MCP app is rendering and you find an iframe nested inside another iframe. Frédéric Barthelet traces why each simpler approach fails: `srcdoc` shares the parent origin so ChatGPT's CSP blocks all third party scripts; relaxing that CSP lets any app read ChatGPT's localStorage and cookies; adding `sandbox` removes origin indexed storage; adding `allow-same-origin` to restore it is the classic sandbox escape. The double iframe is what remains after ruling all of that out. The outer iframe serves one lightweight script from a controlled subdomain (different subdomain per app to prevent cross app storage collisions), which loads the actual app HTML via `srcdoc` into the inner frame — the same pattern Facebook first shipped for their app marketplace. The practical implication: every external domain your view touches must be declared in your MCP app metadata or the submission gets rejected. Barthelet demos Skybridge's CSP inspector, which diffs declared domains against actual network calls live in dev. Speaker info: - https://x.com/bartheletf - https://www.linkedin.com/in/frederic-barthelet/ - https://github.com/fredericbarthelet --- Watch along with the corrected transcript, summary, timestamps and resources on this talk's official AIE page: https://ai.engineer/talks/c-2eEv2ou7Y-why-mcp-and-chatgpt-apps-use-double-iframes-frederic-barthelet-alpic Join our upcoming AI Engineer conferences (see https://ai.engineer landing page): - AIEi Shanghai, November 5–6 — the first for meeting top Chinese labs and engineers - AIE CODE in SF, November 10–12 — the top AI Coding conference returns - AIEi Sydney, December 7–8 — the first AIEi run alongside NeurIPS 2026 in Sydney --- canonical: >- https://liquidgold.cc/channel/aidotengineer/explore/video/why-mcp-and-chatgpt-apps-use-double-iframes-frederi-810ba0c07bc4 markdown: >- https://liquidgold.cc/channel/aidotengineer/video/why-mcp-and-chatgpt-apps-use-double-iframes-frederi-810ba0c07bc4.md llms: null parent: 'https://liquidgold.cc/channel/aidotengineer.md' channel: aidotengineer updated: '2026-10-24T09:41:09.832Z' language: null children: [] videoId: c-2eEv2ou7Y durationSeconds: 1211 publishedAt: '2026-06-15T14:00:06.000Z' searchChunks: - ordinal: 0 text: null startSeconds: 26 endSeconds: 159 watch: 'https://liquidgold.cc/watch/c-2eEv2ou7Y?t=26' heldReason: rights - ordinal: 1 text: null startSeconds: 26 endSeconds: 159 watch: 'https://liquidgold.cc/watch/c-2eEv2ou7Y?t=26' heldReason: rights - ordinal: 2 text: null startSeconds: 170 endSeconds: 263 watch: 'https://liquidgold.cc/watch/c-2eEv2ou7Y?t=170' heldReason: rights - ordinal: 3 text: null startSeconds: 170 endSeconds: 263 watch: 'https://liquidgold.cc/watch/c-2eEv2ou7Y?t=170' heldReason: rights - ordinal: 4 text: null startSeconds: 274 endSeconds: 374 watch: 'https://liquidgold.cc/watch/c-2eEv2ou7Y?t=274' heldReason: rights - ordinal: 5 text: null startSeconds: 386 endSeconds: 486 watch: 'https://liquidgold.cc/watch/c-2eEv2ou7Y?t=386' heldReason: rights - ordinal: 6 text: null startSeconds: 496 endSeconds: 576 watch: 'https://liquidgold.cc/watch/c-2eEv2ou7Y?t=496' heldReason: rights - ordinal: 7 text: null startSeconds: 496 endSeconds: 576 watch: 'https://liquidgold.cc/watch/c-2eEv2ou7Y?t=496' heldReason: rights - ordinal: 8 text: null startSeconds: 587 endSeconds: 699 watch: 'https://liquidgold.cc/watch/c-2eEv2ou7Y?t=587' heldReason: rights - ordinal: 9 text: null startSeconds: 587 endSeconds: 699 watch: 'https://liquidgold.cc/watch/c-2eEv2ou7Y?t=587' heldReason: rights - ordinal: 10 text: null startSeconds: 711 endSeconds: 843 watch: 'https://liquidgold.cc/watch/c-2eEv2ou7Y?t=711' heldReason: rights - ordinal: 11 text: null startSeconds: 711 endSeconds: 843 watch: 'https://liquidgold.cc/watch/c-2eEv2ou7Y?t=711' heldReason: rights - ordinal: 12 text: null startSeconds: 853 endSeconds: 942 watch: 'https://liquidgold.cc/watch/c-2eEv2ou7Y?t=853' heldReason: rights - ordinal: 13 text: null startSeconds: 953 endSeconds: 1045 watch: 'https://liquidgold.cc/watch/c-2eEv2ou7Y?t=953' heldReason: rights - ordinal: 14 text: null startSeconds: 1045 endSeconds: 1211 watch: 'https://liquidgold.cc/watch/c-2eEv2ou7Y?t=1045' heldReason: rights - ordinal: 15 text: null startSeconds: 1045 endSeconds: 1211 watch: 'https://liquidgold.cc/watch/c-2eEv2ou7Y?t=1045' heldReason: rights --- # Why MCP and ChatGPT Apps Use Double Iframes — Frédéric Barthelet, Alpic Inspect ChatGPT's DOM while an MCP app is rendering and you find an iframe nested inside another iframe. Frédéric Barthelet traces why each simpler approach fails: \`srcdoc\` shares the parent origin so ChatGPT's CSP blocks all third party scripts; relaxing that CSP lets any app read ChatGPT's localStorage and cookies; adding \`sandbox\` removes origin indexed storage; adding \`allow-same-origin\` to restore it is the classic sandbox escape. The double iframe is what remains after ruling all of that out. The outer iframe serves one lightweight script from a controlled subdomain (different subdomain per app to prevent cross app storage collisions), which loads the actual app HTML via \`srcdoc\` into the inner frame — the same pattern Facebook first shipped for their app marketplace. The practical implication: every external domain your view touches must be declared in your MCP app metadata or the submission gets rejected. Barthelet demos Skybridge's CSP inspector, which diffs declared domains against actual network calls live in dev. Speaker info: - https://x.com/bartheletf - https://www.linkedin.com/in/frederic-barthelet/ - https://github.com/fredericbarthelet --- Watch along with the corrected transcript, summary, timestamps and resources on this talk's official AIE page: https://ai.engineer/talks/c-2eEv2ou7Y-why-mcp-and-chatgpt-apps-use-double-iframes-frederic-barthelet-alpic Join our upcoming AI Engineer conferences (see https://ai.engineer landing page): - AIEi Shanghai, November 5–6 — the first for meeting top Chinese labs and engineers - AIE CODE in SF, November 10–12 — the top AI Coding conference returns - AIEi Sydney, December 7–8 — the first AIEi run alongside NeurIPS 2026 in Sydney --- Canonical: https://liquidgold.cc/channel/aidotengineer/explore/video/why-mcp-and-chatgpt-apps-use-double-iframes-frederi-810ba0c07bc4 · Channel: [AI Engineer](https://liquidgold.cc/channel/aidotengineer.md) > Search chunk text is held until public-source provenance is verified. ## Document chunks > Missing: no stored document chunks are available.