Run Claude Code and Codex on the same project without overwriting each other.

What goes wrong

An agent edits a file in three steps: it reads the file, works out the change, and saves the new version. That takes seconds to minutes.

If Claude Code and Codex both work on the same file in that window, the second save can replace the first one's changes. Or one agent keeps building on a version of the file that no longer exists.

The fix is always the same idea: make sure two agents never change the same file at the same time. There are four ways to do that.

1Give them separate files or separate tasks

The simplest way. Give each agent its own part of the project: Claude Code works on the website pages, Codex on the server code. Or one writes the feature while the other only reviews and reports back without editing.

• Fits when

  The work splits cleanly by folder or by job.

• Breaks when

  Both tasks need the same shared file, like a settings file or a main page.

2Separate git worktrees, merged afterwards

Git is the tool most projects use to track changes. A worktree is a second copy of your project folder on its own branch (a separate line of changes). Each agent edits its own copy, so their edits can't collide. When both are done, you merge the branches back together.

How each tool does it, per their own docs

• Claude Code: claude --worktree feature-auth (or -w) starts a session in a new worktree under .claude/worktrees/, on a new branch named worktree-feature-auth.
• Codex desktop app: choose Worktree when you start a new chat, and pick the branch to start from.
• Codex CLI: its command reference lists no worktree option. Make one with git, then start Codex in that folder:

git worktree add ../project-feature-a -b feature-a
codex --cd ../project-feature-a

Cleaning up: git worktree list shows them, git worktree remove deletes one when you're done.

• Fits when

  Both agents need to touch the same files, or the tasks are big.

• Costs you

  A merge at the end. If both changed the same lines, git reports a conflict and someone has to choose. Worktrees also need git, and at least one commit so each copy starts with your files.

3Take turns

Run one agent at a time. Claude Code builds, then Codex reviews or fixes, then back again. Nothing can collide because only one agent is editing.

• Fits when

  The second agent's job depends on the first one's result, like a review.

• Costs you

  Speed: one agent always waits. And you have to remember to start the next one.

4File locks: how Technically Not does it

Technically Not runs Claude Code, Codex and other agent CLIs side by side in terminal panels on the same project. Its file locks let one agent edit a file at a time, so they can share the folder:

• Claude Code takes the lock by itself

  When it's about to edit a file another agent holds, the edit is refused, with the holder's name and what to do instead: tnai send the holder to split the work, or do something else and try later.

• Other CLIs lock files themselves

  Codex and the others have no check before an edit, so Technically Not instructs them to run tnai lock FILE first. That works when the agent follows the instruction.

• The holder hears about it

  It gets a short message saying who wanted its file, so the two can agree who does what.

• Locks end by themselves

  On tnai unlock, when the holder's terminal panel stops or closes, or 20 minutes after its last edit of that file. tnai locks shows who holds what.

Which one to pick

What it costs

Separate files, worktrees and taking turns are free.

Questions

Sources