Codex

Codex Skill

Run OpenAI Codex CLI for code analysis, reviews, and automated editing. Defaults to gpt-5.3-codex with preset reasoning effort per mode.

Quick Start

# PR review (posts inline comments to GitHub)
/codex review #123

# Plan review
/codex review-plan @plan-slug
/codex review-plan ./path/to/plan.md

# Spec review
/codex review-spec @spec-slug

# General task
/codex "refactor the parser module for clarity"

# Resume last session
/codex resume
/codex resume "follow-up prompt"

Modes and Reasoning Presets

Model: gpt-5.3-codex unless the user specifies otherwise.

Sandbox: danger-full-access for all modes. Codex has full filesystem and network access — same trust level as Claude. This lets it use gh for GitHub API calls and kspec for spec/task operations directly.

Users can override reasoning (-c model_reasoning_effort="xhigh") or model (-m gpt-5.2) explicitly.

PR Review Mode

/codex review #123
/codex review @task-ref

Resolving @task-ref to PR Number

When the user provides a @task-ref instead of a PR number:

# Check task for vcs_refs
kspec task get @task-ref --json | jq '.vcs_refs'

# Or search for PR by task trailer in body/commits
gh pr list --search "Task: @task-ref" --json number,url,title

If no PR is found, error: "No PR found for task @task-ref. Create a PR first with /pr."

Flow

For straightforward diff review, prefer the native codex exec review subcommand:

codex exec \
  -m gpt-5.3-codex \
  -c model_reasoning_effort="high" \
  -s danger-full-access \
  --skip-git-repo-check \
  review \
  "$(cat <<'PROMPT'
Also check for:
- Spec context discovery: check PR body, commit messages, and changed file `// AC:` annotations for Task:/Spec: references. Also run `kspec tasks list` and match by title/description to PR scope. If a task ref is found, resolve to spec via `kspec task get @task-ref`. If any spec is found, validate AC coverage below. Only skip AC checks if genuinely no spec exists.
- Own AC coverage: every spec AC should have test with `// AC: @spec-ref ac-N` annotation
- Trait AC coverage: run `kspec item get @spec-ref` to find inherited trait ACs. Each needs test with `// AC: @trait-slug ac-N` annotation
- Run `kspec validate` — any trait AC coverage warnings are MUST-FIX
- Spec alignment: implementation matches spec intent
- Code quality: duplicated logic, ignored shared utilities, inconsistent patterns
- Test quality: no fluff tests, prefer E2E over unit

After reviewing, post your review to GitHub using `gh pr review <NUMBER>`.
For inline comments, write a JSON body to /tmp/codex-pr-review-body.json with this structure:
  {"event":"COMMENT","body":"summary","comments":[{"path":"src/file.ts","line":42,"body":"comment"}]}
Then post: gh api repos/{owner}/{repo}/pulls/<NUMBER>/reviews --method POST --input /tmp/codex-pr-review-body.json

Also write the full review to /tmp/codex-pr-<NUMBER>-review.md

Severity levels: MUST-FIX, SHOULD-FIX, SUGGESTION.
PROMPT
)"

For PR reviews that need additional context (task ref, spec ACs), use codex exec instead:

codex exec \
  -m gpt-5.3-codex \
  -c model_reasoning_effort="high" \
  -s danger-full-access \
  --skip-git-repo-check \
  "$(cat <<'PROMPT'
Review PR #123 in this repository.

1. Get the PR diff: `gh pr diff 123`
2. Get PR details: `gh pr view 123 --json title,body,files`
3. Check the PR body for `Task: @task-ref` or `Spec: @spec-ref` trailers:
   - If `Task:` found: `kspec task get @task-ref` to get spec_ref, then `kspec item get @spec-ref`
   - If `Spec:` found: `kspec item get @spec-ref` directly
   - Either way, check acceptance criteria coverage
4. Review the code for:
   - Correctness and potential bugs
   - Own AC coverage: every spec AC should have test with `// AC: @spec-ref ac-N` annotation
   - Trait AC coverage: run `kspec item get @spec-ref` to find inherited trait ACs (under "Inherited from @trait-slug" sections). Each needs test with `// AC: @trait-slug ac-N` annotation
   - Run `kspec validate` — trait AC coverage warnings are MUST-FIX
   - Spec alignment: implementation matches spec intent, not just syntax
   - Code quality: duplicated logic, ignored shared utilities, inconsistent patterns
   - Test quality: no fluff tests, prefer E2E over unit
5. Write a review body JSON file to /tmp/codex-pr-review-body.json:
   {"event":"COMMENT","body":"summary","comments":[{"path":"file","line":N,"body":"comment"}]}
   Then post: gh api repos/{owner}/{repo}/pulls/123/reviews --method POST --input /tmp/codex-pr-review-body.json
6. Also write the full review to /tmp/codex-pr-123-review.md

If no Task or Spec trailer exists in the PR body, dig deeper before skipping AC checks:
   a. Check commit messages for Task: or Spec: trailers
   b. Search recent tasks: run `kspec tasks list` and match by title/description to PR scope
   c. Check if changed files have `// AC: @spec-ref` annotations pointing to specs
   d. If a task ref is found, resolve to spec: `kspec task get @task-ref --json | jq '.spec_ref'`
   e. If a spec is found through any of these methods, validate AC coverage identically to the trailer-present case
   f. Only fall back to pure code review if genuinely no spec exists for the changed behavior

Severity levels: MUST-FIX, SHOULD-FIX, SUGGESTION.
PROMPT
)"

AC Coverage Check

When a task ref is provided, Codex is instructed to verify:

• Every own AC has test coverage via // AC: @spec-ref ac-N annotations
• Every inherited trait AC has test coverage via // AC: @trait-slug ac-N annotations
• kspec validate shows no trait AC coverage warnings for the spec
• Missing coverage (own or trait) is flagged as MUST-FIX
• Spec alignment: implementation matches spec intent, not just syntax

Integration with /pr-review

For full quality-gate PR review (CI verification, merge decision), use /pr-review @task-ref instead. This skill focuses on code-level review feedback — use both together:

/codex review #123          # Codex posts inline code review
/pr-review @task-ref        # Full quality gate workflow (AC, CI, merge)

Plan Review Mode

/codex review-plan @plan-slug
/codex review-plan ./path/to/plan.md

What Codex Checks

Codex can read plans directly via kspec plan get or from a file path:

codex exec \
  -m gpt-5.3-codex \
  -c model_reasoning_effort="high" \
  -s danger-full-access \
  --skip-git-repo-check \
  "Review the plan. Get it with: kspec plan get @plan-slug (or read <path>). $(cat <<'PROMPT'
Evaluate against these criteria and write feedback to /tmp/codex-plan-review.md:

## Structure
- Has ## Specs section with YAML array?
- Has ## Tasks section with derive_from_specs line?
- Has ## Implementation Notes section?

## Spec Quality
- Every spec has `title` (required)
- Every spec has `acceptance_criteria` array (strongly recommended)
- Each AC has id, given, when, then fields
- AC `then` clauses are concrete and testable (not vague like "works correctly")
- AC are independently testable (not compound)
- `parent` references use @ prefix and point to valid specs
- `traits` reference valid trait names with @ prefix
- `type` is a valid item type (feature, requirement, constraint, decision)

## Completeness
- Implementation notes present for complex specs
- No obvious gaps in AC coverage (behaviors described but not covered by AC)
- Specs don't overlap or duplicate each other
- Dependencies between specs are explicit

## Red Flags
- Vague AC: "then: system behaves correctly"
- Untestable AC: "then: performance is acceptable"
- Over-granular AC: one AC per line of code
- Compound AC: "X and Y and Z" in single criterion
- Missing parent for nested items
- Trait applied to fewer than 3 specs

Format: Use ## headers for sections, bullet lists for issues.
Rate severity: MUST-FIX, SHOULD-FIX, SUGGESTION.
PROMPT
)"

Output

Feedback is written to /tmp/codex-plan-review.md. After Codex completes:

# Show the user the output path
echo "Plan review written to /tmp/codex-plan-review.md"

# Optionally display summary
head -50 /tmp/codex-plan-review.md

Spec Review Mode

/codex review-spec @spec-slug
/codex review-spec @module-slug    # Review entire module

What Codex Checks

Codex can read specs directly via kspec item get and validate with kspec validate:

codex exec \
  -m gpt-5.3-codex \
  -c model_reasoning_effort="high" \
  -s danger-full-access \
  --skip-git-repo-check \
  "Review the spec. $(cat <<'PROMPT'
Get the spec with: kspec item get @spec-slug
For module-level review: kspec item list --module @module-slug to get all items, then kspec item get each one.
Also run kspec validate for structural issues.

Evaluate and write feedback to /tmp/codex-spec-review.md:

## Acceptance Criteria Quality
- Are all ACs concrete and independently testable?
- Do `then` clauses describe observable outcomes (not internal state)?
- Are ACs atomic (not compound "X and Y and Z")?
- Is coverage complete (all described behaviors have ACs)?
- Are there ACs that overlap or contradict each other?

## Structure
- Appropriate item type for content?
- Description clearly explains purpose?
- References (depends_on, implements, relates_to) are valid?
- Status fields consistent (maturity vs implementation)?

## Trait Usage
- Applied traits are appropriate (behavior applies to this spec)?
- Cross-cutting behaviors that appear 3+ times should use traits
- Trait ACs don't conflict with spec-specific ACs

## Testability
- Can each AC be validated with automated tests?
- Are preconditions (given) realistic and reproducible?
- Are actions (when) specific enough to implement?

Format: ## headers, bullet lists, severity ratings.
MUST-FIX | SHOULD-FIX | SUGGESTION
PROMPT
)"

Output

Written to /tmp/codex-spec-review.md.

General Mode

/codex "analyze the error handling patterns in src/cli/"
/codex "refactor parser module for clarity"

Defaults

• Model: gpt-5.3-codex
• Reasoning: medium
• Sandbox: danger-full-access

Command Assembly

codex exec \
  -m gpt-5.3-codex \
  -c model_reasoning_effort="medium" \
  -s danger-full-access \
  --skip-git-repo-check \
  "Your prompt here. Write output to /tmp/codex-output.md"

Resuming Sessions

# Resume last session with new prompt (positional arg)
codex exec --skip-git-repo-check resume --last "follow-up prompt"

# Resume last session with prompt from stdin
echo "follow-up prompt" | codex exec --skip-git-repo-check resume --last -

# Resume with no additional prompt
codex exec --skip-git-repo-check resume --last

When resuming, config flags (-c, -m, -s) are accepted and override the original session's settings. All flags must go between exec and resume.

Output Convention

All Codex output is written to /tmp/codex-* files:

After every Codex run:

1. Report the output file path to the user
2. Summarize key findings
3. For PR reviews, also post comments to GitHub via gh

Error Handling

• If codex exec exits non-zero, report the error and ask the user how to proceed
• If output file is empty or missing, Codex may have hit a context or timeout issue — re-run without stderr suppression to diagnose
• For review modes, do NOT suppress stderr — review errors (auth failures, API issues) should be visible
• For general mode, append 2>/dev/null to suppress thinking tokens unless debugging

Preflight Checks

Before PR review, verify gh auth is working:

gh auth status

If auth fails, instruct the user to run gh auth login before retrying.

Overrides

Users can override any preset:

/codex review #123 --model gpt-5.2 -c model_reasoning_effort="xhigh"
/codex "prompt" -c model_reasoning_effort="high"

Parse overrides from the user's message and map to CLI flags:

• --model X or -m X → -m X
• --effort X → -c model_reasoning_effort="X" (translate to config flag)

Handling Complex Prompts

When prompts contain shell-unsafe characters (quotes, backticks, special characters, or multi-line content), use the prompt-file pattern instead of inline quoting:

# 1. Write prompt to temp file (use mktemp for safety)
PROMPT_FILE=$(mktemp /tmp/codex-prompt.XXXXXX)
cat > "$PROMPT_FILE" << 'EOF'
Review the code for:
- Edge cases with special chars like `$var` and "quoted" strings
- Multi-line logic that's hard to escape inline
- Patterns matching {curly} braces
EOF

# 2. Use $(cat file) to inject the prompt
codex exec \
  -m gpt-5.3-codex \
  -c model_reasoning_effort="medium" \
  -s danger-full-access \
  --skip-git-repo-check \
  "$(cat "$PROMPT_FILE")"

# 3. Clean up
rm -f "$PROMPT_FILE"

When to Use This Pattern

Why Prompt-File Over Heredocs?

Quoted heredocs (<<'DELIM'...DELIM) handle quotes, backticks, and $ literally — they don't cause parsing failures. However, the prompt-file pattern offers practical advantages:

• Delimiter collision: If your prompt contains the delimiter string itself, heredocs fail
• Mixed expansion: When you need $var expanded in some places but literal in others, heredocs require awkward escaping
• Debuggability: You can cat "$PROMPT_FILE" to verify exact content before running
• Reusability: Same prompt file can be used across multiple commands

For simple prompts, heredocs work fine. Use prompt-files when prompts are complex, generated dynamically, or need inspection before use.

Agent Dispatch Safety Guard

When invoking Codex from inside an agent dispatch session, you MUST inject safety constraints into every codex prompt. Codex runs with danger-full-access and has no awareness of the agent runtime hosting it.

Detection

Before running any codex exec command, check for agent dispatch context:

# Env var set by agent runtime on spawned agent processes
if [ -n "$KSPEC_SESSION_ID" ]; then
  # We're inside an agent dispatch session — inject safety guard
fi

Required Safety Preamble

When agent dispatch context is detected, prepend this safety block to every codex prompt:

SAFETY CONSTRAINTS (you are running inside a kspec agent dispatch session):
- NEVER start kspec agent run, kspec serve, or any long-running kspec process
- NEVER use pkill, kill, killall, or any process-killing command targeting kspec processes
- NEVER run commands that would terminate or interfere with the parent agent session
- Do NOT run CLI spot-checks that start background services
- If you need to verify CLI behavior, use non-destructive read-only commands only
Violating these constraints will kill the automation session hosting you.

Example (PR review with safety guard)

# Detect agent dispatch context
AGENT_GUARD=""
if [ -n "$KSPEC_SESSION_ID" ]; then
  AGENT_GUARD="SAFETY CONSTRAINTS (you are running inside a kspec agent dispatch session):
- NEVER start kspec agent run, kspec serve, or any long-running kspec process
- NEVER use pkill, kill, killall, or any process-killing command targeting kspec processes
- NEVER run commands that would terminate or interfere with the parent agent session
- Do NOT run CLI spot-checks that start background services
- If you need to verify CLI behavior, use non-destructive read-only commands only
Violating these constraints will kill the automation session hosting you.

"
fi

codex exec \
  -m gpt-5.3-codex \
  -c model_reasoning_effort="high" \
  -s danger-full-access \
  --skip-git-repo-check \
  "${AGENT_GUARD}Review PR #123 in this repository. ..."

Why This Matters

In a previous automation session, Codex ran a "CLI spot-check" that accidentally started a long-running kspec process, then ran pkill to clean up — which killed the actual automation session hosting it. The session died mid-tool-call with no clean exit.

Tips

• Always use --skip-git-repo-check — this project uses a shadow branch worktree that confuses Codex's git detection
• For large diffs, pipe through head -2000 before giving to Codex to stay within context
• Codex has full access and can run gh, kspec, npm, etc. directly — instruct it to use these tools in your prompt
• Tell Codex to run kspec from the project root, not from inside .kspec/ (same gotcha agents hit)
• Use codex exec review for straightforward diff reviews (has --base, --commit, --uncommitted flags built in)
• Do NOT use --full-auto — it forces workspace-write sandbox, overriding danger-full-access
• Do NOT use REQUEST_CHANGES review event — reviews are posted from the repo owner's account, and GitHub prohibits requesting changes on your own PR. Use COMMENT for findings or APPROVE when clean.