Codex CLI

Reference for driving codex exec correctly from an agent session. For a full review gate with a fix-or-rebut loop, use the codex-gate skill instead.

Invocation rules

• Do not pass -m. ~/.codex/config.toml sets the default model; override it only when the user names a model. Pair reviews with -c model_reasoning_effort="xhigh" (options: none, minimal, low, medium, high, xhigh).
• Always redirect stdin from /dev/null. codex exec appends stdin to the prompt, so without the redirect it blocks on an open terminal and looks like a slow reasoning pass until killed. The tell is empty stdout with Reading additional input from stdin... on stderr.
• Append 2>/dev/null to hide thinking tokens (stderr). Show stderr only when debugging.
• Sandbox: --sandbox read-only for reviews, workspace-write for edits, danger-full-access only for work that needs the network. --full-auto was removed (codex-cli 0.160 rejects it with unexpected argument); a workspace-write exec run edits without it. Ask before danger-full-access or --skip-git-repo-check unless the user already granted it.
• -C <dir> runs from another directory; --skip-git-repo-check is needed outside a repository.
• -i <file> attaches an image and takes a list of files, so it swallows a prompt placed after it (the run then fails with No prompt provided via stdin). Put the prompt before any -i flags, or repeat -i per file after the prompt.
• Pass -o <file> when the final message must survive scrollback.

Reviews

codex exec review accepts a scope flag (--base <branch>, --commit <sha>, --uncommitted) or a custom prompt, never both; combining them fails arg parsing with the argument '--base <BRANCH>' cannot be used with '[PROMPT]' (codex-cli 0.146 through 0.154). So:

• Codex's own review instructions on a scope: codex exec review --base main </dev/null 2>/dev/null
• Your own instructions: plain codex exec with the scope stated in the prompt, for example codex exec --sandbox read-only "<instructions>. Review only the changes on this branch relative to main; see them with git diff main...HEAD." </dev/null 2>/dev/null

Resuming

codex exec resume --last "<prompt>" </dev/null 2>/dev/null continues the previous session with its original model, reasoning effort, and sandbox; do not pass configuration flags when resuming unless the user asks. After any run, tell the user the session can be resumed this way.

Quick reference

After a run

Summarize the outcome. When the output has actionable findings, offer to resume the session to apply them; do not apply or commit changes on the user's behalf without being asked. Stop and report when codex exits non-zero or returns partial results, and ask how to proceed.