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Greg Isenberg
"Codex Sites" Clearly Explained (and how to use it)
⏱ 25 min video · 4 min read4 Jun 2026
TL;DR
Greg Isenberg walks through what Codex Sites is, how it compares to Replit and Lovable, and live-builds a startup ideas OS to demonstrate six core best practices: memory, safe actions, skills, save-gating, and autonomous update loops. The key insight is that Codex Sites is less of a no-code builder and more of a foundation for apps that agents can keep updating autonomously.
Key points
1
Codex Sites is invoked as a plugin inside Codex (using @sites) and is best suited for people already living in the Codex ecosystem who want autonomous, self-updating apps rather than a one-prompt full-stack builder.
2
Unlike Replit or Lovable, Codex Sites currently lacks built-in auth, databases, payments, email, analytics, and a secrets vault — so it requires more technical prompting to get full functionality.
3
Adding persistent memory requires explicitly prompting Codex to set up a database (it uses Cloudflare D1 by default); without this, the app resets and is just a demo.
4
Safe actions are pre-approved API mutations (e.g. add idea, move card) that let Codex agents update the live app autonomously from any chat, without executing arbitrary SQL or triggering deploys.
5
Skills are reusable instruction manuals saved to Codex so future chat sessions know how to operate the app — critical for enabling the autonomous update loop that makes Codex Sites genuinely powerful.
Actionable insights
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Always invoke Codex Sites with @sites and include 'save for review, do not deploy' in your first prompt — this prevents premature deployment and lets you inspect before going live.
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Before coding storage, ask Codex to show you the data model and required actions first; this tells non-technical users exactly which safe actions to create without guessing.
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Create a named Codex skill for every app you build (e.g. 'startup ideas admin') — this lets any future chat thread operate the app using only approved safe actions, enabling true agent-driven automation.
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Use save-gating checkpoints (e.g. 'save as V1 review, do not deploy') before major milestones to avoid losing progress, since Codex does not auto-save.
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To prove the autonomous loop works, open a brand new chat, invoke the skill, and ask it to add data to the live app — if it updates correctly via safe actions only, the autonomous pipeline is functioning.
Notable quotes
“I used to run a web design agency — one of the things I used to say was, a website is a living and breathing entity. We are now in 2026 where the agents are actually doing the updating, the editing, the removing.”
“A lot of people are going to use Codex Sites to make personal web pages and little apps. But I actually think that the real unlock here is to make products that Codex can keep operating for you.”
“Is it the most beautiful website on the planet? No. Does it work? Yes.”
Worth watching?
⏭️
Worth watching the full video?
The structured summary captures all six techniques and the live-build walkthrough in detail — watch the video only if you want to see the actual Codex interface and UI while following along in real time.
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