Codex++ prompt experiment

This repository contains two model-instructions snapshots for comparing Codex CLI behavior:

• codex_2026_07_24_original.md is the default base-instructions file from the OpenAI Codex repository on July 24, 2026.
• ext_2026_07_24_port.md is an alternative prompt port adapted for Codex, with source-specific tool names, product references, model information, and environment data translated or removed.

View the full instruction diff.

Codex already supports loading base instructions from a local file. You do not need to download or compile a custom executable.

Quick start

Download the ported prompt into your Codex configuration directory:

mkdir -p ~/.codex/prompts
wget -O ~/.codex/prompts/ext_2026_07_24_port.md \
  https://raw.githubusercontent.com/jtippett/codexplusplus/main/ext_2026_07_24_port.md

Then start Codex with the override:

codex -c 'model_instructions_file="~/.codex/prompts/ext_2026_07_24_port.md"'

Codex expands ~, so an absolute path is not required.

If wget is unavailable, use:

curl -fL \
  https://raw.githubusercontent.com/jtippett/codexplusplus/main/ext_2026_07_24_port.md \
  -o ~/.codex/prompts/ext_2026_07_24_port.md

Create a codexx alias

To launch the modified configuration with the shorter codexx command, add this alias to your shell configuration:

alias codexx="codex -c 'model_instructions_file=\"~/.codex/prompts/ext_2026_07_24_port.md\"'"

For zsh, add it to ~/.zshrc, then reload the file:

source ~/.zshrc

For Bash, add it to ~/.bashrc, then run source ~/.bashrc. You can then use codexx anywhere you would normally use codex, including with additional arguments:

codexx
codexx exec "Explain this repository"

Run non-interactively

The same override works with codex exec:

codex -c 'model_instructions_file="~/.codex/prompts/ext_2026_07_24_port.md"' exec "Explain this repository"

Compare with the Codex baseline

Download the baseline prompt:

wget -O ~/.codex/prompts/codex_2026_07_24_original.md \
  https://raw.githubusercontent.com/jtippett/codexplusplus/main/codex_2026_07_24_original.md

Then run the same task once with each file:

codex -c 'model_instructions_file="~/.codex/prompts/codex_2026_07_24_original.md"' exec "Your evaluation task"

codex -c 'model_instructions_file="~/.codex/prompts/ext_2026_07_24_port.md"' exec "Your evaluation task"

Use a fresh session for each run so earlier conversation context does not affect the comparison.

Run from a clone

Relative paths also work. Codex resolves them against its effective working directory:

git clone https://github.com/jtippett/codexplusplus.git
cd codexplusplus
codex -c 'model_instructions_file="ext_2026_07_24_port.md"'

If you start Codex from another directory, use the home-relative path from the quick start or point the override at the file relative to that directory.

Make the override persistent

To use the ported prompt by default, add this to ~/.codex/config.toml:

model_instructions_file = "~/.codex/prompts/ext_2026_07_24_port.md"

Remove that line to return to Codex's built-in model instructions. A command-line -c override applies only to that invocation.

What the override changes

model_instructions_file replaces the selected model's base instructions. Codex still supplies the real tool schemas and its dynamic context, including permissions, sandbox policy, AGENTS.md, skills, apps, plugins, collaboration mode, and current environment information.

The port maps external agent concepts to Codex equivalents such as:

• Bash, Read, Edit, and Write to exec_command and apply_patch
• task tracking to update_plan
• subagents to conditional spawn_agent usage
• skills and web tools to Codex's available skill and web mechanisms
• repository guidance to AGENTS.md

The override was validated with codex-cli 0.145.0.