The Codex-Claude Code Workflow: How I Plan With GPT-5 and Execute With Claude Code

I used to dive straight into Claude Code’s Plan Mode and ask it to build features.

Sometimes it worked brilliantly – Claude would research, plan, and implement perfectly. Other times, despite Plan Mode’s capabilities, it built something that technically worked but wasn’t quite what I had in mind.

The problem?

Even with Plan Mode, I wasn’t always giving Claude Code enough context about my specific requirements.

I was expecting it to infer implementation details, UI decisions, and edge cases from a brief description.

Then I discovered a game-changing workflow: Use Codex to plan meticulously, then Claude Code to execute flawlessly.

Let me show you exactly how this works with a real example – adding a context menu to rename and delete chat sessions in my YouTube AI app.

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The Magic Is In The Questions

Here’s the breakthrough:

Instead of jumping straight into implementation, I start by having Codex ask me clarifying questions until it’s 95% confident it can create a perfect plan.

This brilliant approach comes from Sabrina Ramonov’s YouTube video “3 ChatGPT Prompts That Feel Like Millionaire Cheat Codes”.

I’ve refined her prompt to work perfectly with Codex for feature planning.

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Step 1: Start With Questions, Not Code

I begin with this carefully crafted prompt to Codex:

In the Chat sidebar, I want to add context menu for user to rename the session as well as deleting the session.

Help me come up with a plan to implement this. DON'T WRITE OR EDIT ANY FILES.

Ask me clarifying questions until you are 95% confident you can complete this task successfully.

a. If the question is about choosing different options, please provide me with a list of options to choose from. Mark the option with a clear label, like a, b, c, etc.
b. If the question need custom input that is not in the list of options, please ask me to provide the custom input.

The key elements here:

• DON’T WRITE OR EDIT ANY FILES – This keeps Codex focused on planning
• 95% confidence threshold – Forces thorough understanding before proceeding
• Structured options – Makes decision-making faster and reveals possibilities I hadn’t considered

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Step 2: The Clarifying Questions Phase

This is where the magic happens. Codex doesn’t just ask random questions – it systematically explores every aspect of the feature:

Notice how Codex provides options for each decision:

• Rename UI: Dialog with text input, inline edit, or popover
• Delete confirmation: AlertDialog, no confirmation, or typing “DELETE”
• Mobile behavior: Different menu types or desktop-only
• Post-action behavior: Keep selection, reset, or select next

I can quickly pick options without having to type lengthy explanations:

But Codex doesn’t stop there. It asks follow-up questions to refine the details:

Questions about:

• Handling duplicate titles
• Whitespace validation
• Button visibility
• Delete confirmation text
• Test IDs for E2E testing

I continue answering:

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Step 3: The Comprehensive Plan

After gathering all requirements, Codex produces a detailed implementation plan:

The plan is incredibly thorough, covering:

Backend Architecture:

• PATCH and DELETE routes with exact endpoints (/api/chat/sessions/:sessionId)
• Specific HTTP status codes (200, 204, 401, 404)
• Storage interface methods with complete signatures
• MemStorage and PostgreSQLStorage implementation details
• Ownership verification and cascade deletion logic

Client-Side Implementation:

• useChat hook extensions with renameSessionMutation and deleteSessionMutation
• Cache invalidation strategies
• Toast feedback for success/error states
• Context state management

UI Components:

• ContextMenu wrapper with ContextMenuTrigger
• Always-visible “…” actions button with DropdownMenu
• Dialog components with specific state management
• Input validation rules (trim, non-empty, allow duplicates)
• Loading states that disable actions during pending operations

UX Specifications:

• Left-click for selection, right-click for actions
• Mobile-first “…” button approach
• Preserved updatedAt timestamps during rename
• Session order stability
• Sidebar sheet behavior (no auto-close on dialog open)

Testing Infrastructure:

• Comprehensive test IDs for E2E testing
• API contract examples with request/response formats
• Testing checklist with specific scenarios

This isn’t just a vague outline – it’s a blueprint that any developer could follow.

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Step 4: From Plan to Implementation

Now comes the handoff. I copy Codex’s plan and paste it directly into Claude Code:

Claude Code immediately understands the comprehensive plan:

Watch as Claude Code systematically implements each part of the plan:

The implementation is surgical and precise – Claude Code knows exactly what to build because the plan is so detailed:

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Step 5: The Review Loop

But we’re not done yet. This is where the workflow truly shines.

I take the git diff from Claude Code’s implementation and ask Codex to review it:

Please read the git diff, analyze the implementation and check if everything is implemented as per advised.

DON'T WRITE OR EDIT ANY FILES.

Codex meticulously reviews every change:

In this case, Codex found two deviations from the agreed plan:

1. Timestamp updates during rename (should be preserved)
2. Button visibility on desktop (had unnecessary opacity classes)

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Step 6: Refinement Based on Feedback

I copy Codex’s feedback back to Claude Code:

Claude Code immediately understands and implements the corrections:

The final result?

A perfectly implemented feature that matches the original specifications exactly:

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Why This Workflow Is Revolutionary

1. Thinking Before Coding

By forcing myself to answer Codex’s questions, I’m thinking through edge cases and implementation details BEFORE any code is written.

This prevents the “oh wait, what about…” moments during development.

2. Leveraging Strengths

• Codex excels at: Analysis, planning, asking the right questions, and meticulous review
• Claude Code excels at: Understanding context, implementing complex features, and following detailed plans

3. Faster Development

Counter-intuitively, spending 10 minutes on planning saves hours of refactoring.

The implementation is right the first time.

4. Better Code Quality

The review loop catches issues that might slip through.

Having Codex review Claude Code’s work is like having a senior developer review every PR.

5. Learning Through Questions

Codex’s questions often reveal considerations I hadn’t thought of.

“Should duplicate titles be allowed?”
“What happens to the selection after delete?”

These questions make me a better developer.

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The Prompt That Makes It Work

The secret sauce is in the prompt structure. By combining:

• Clear feature description
• Explicit “don’t code” instruction
• 95% confidence threshold (credit to Sabrina Ramonov)
• Structured option format

We transform Codex from a code generator into a thoughtful architect who ensures every detail is considered before implementation begins.

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Your Next Feature

Try this workflow on your next feature:

1. Start with Codex – Use the clarifying questions prompt
2. Answer thoughtfully – Pick from options or provide custom input
3. Get the plan – Let Codex create a comprehensive blueprint
4. Implement with Claude Code – Copy the plan and watch it build
5. Review with Codex – Check the implementation against the plan
6. Refine with Claude Code – Apply any feedback from the review

This isn’t just about building features faster. It’s about building them right the first time.

While the context menu might seem like a simple example, this same workflow scales beautifully to complex features. Whether you’re building authentication systems, real-time collaboration, or intricate data visualizations – the pattern of meticulous planning with Codex followed by precise execution with Claude Code ensures success every time.

What feature will you plan with Codex and build with Claude Code?

P.S. – The combination of Codex’s analytical planning and Claude Code’s implementation prowess has transformed how I develop. No more half-baked features or forgotten edge cases. Just clean, well-planned, thoroughly reviewed code.