Automatic code review

Deliverable: every time Claude Code finishes a turn with uncommitted changes, a Stop hook runs a Codex review of those changes and prints its verdict.

Prerequisites: Claude Code and Codex CLI both configured with the same MIRAPI_API_KEY (see Claude Code and Codex CLI); a git repository.

1. The review script

Create ~/.claude/review.sh:

#!/usr/bin/env bash
# Run a Codex review of the uncommitted changes.
set -euo pipefail

DIFF_STAT=$(git diff HEAD --stat || true)

# Exit silently when there is nothing to review.
if [[ -z "$DIFF_STAT" ]]; then
  exit 0
fi

codex exec "Review the changes below for bugs, security issues, and broken invariants. Be concise.

$DIFF_STAT" 2>/dev/null || true

Make it executable:

chmod +x ~/.claude/review.sh

The script captures a one-line summary of the staged and unstaged changes (git diff HEAD --stat), hands it to Codex, and lets Codex print the review to the hook’s output. The trailing || true keeps a failed Codex call from surfacing as a hook error.

2. The Stop hook

Add the hook to your project’s .claude/settings.json:

{
  "hooks": {
    "Stop": [
      {
        "hooks": [
          {
            "type": "command",
            "command": "bash ~/.claude/review.sh",
            "timeout": 120
          }
        ]
      }
    ]
  }
}

The Stop event fires whenever Claude Code pauses for your input, which is the moment a review is useful. The hook fields are:

Field	Purpose
`type`	`"command"` runs a shell command
`command`	The command to execute (here, `bash ~/.claude/review.sh`)
`timeout`	Maximum seconds the hook may run before being killed (120)

To keep the hook out of git, use .claude/settings.local.json instead; global hooks live in ~/.claude/settings.json.

3. Verify it fires

First test the script on its own: change a tracked file, then run it directly.

bash ~/.claude/review.sh

You should see the Codex review in the terminal. Then ask Claude Code to make a change and wait for the hook output. The verdict appears in the hook’s output section once Claude Code pauses.

Two protocols, one key

Claude Code and Codex CLI speak different protocols, so they use different base URLs on MirAPI:

Agent	Protocol	Base URL	Authentication
Claude Code	Anthropic Messages (`POST /v1/messages`)	`https://api.mirapi.ai` (no `/v1`)	`ANTHROPIC_AUTH_TOKEN=$MIRAPI_API_KEY`
Codex CLI	OpenAI Responses (`POST /v1/responses`)	`https://api.mirapi.ai/v1`	`env_key = "MIRAPI_API_KEY"`

Claude Code

Point the Anthropic client at the bare origin and pass the key through the auth-token variable:

export ANTHROPIC_BASE_URL="https://api.mirapi.ai"
export ANTHROPIC_AUTH_TOKEN="$MIRAPI_API_KEY"
export ANTHROPIC_MODEL="deepseek-chat"

Do not append /v1; Claude Code builds the /v1/messages path itself. See Claude Code for the full setup.

Codex CLI

model = "deepseek-chat"
model_provider = "mirapi"

[model_providers.mirapi]
name = "MirAPI"
base_url = "https://api.mirapi.ai/v1"
env_key = "MIRAPI_API_KEY"
wire_api = "responses"

Codex appends /responses to the base URL, so it needs the /v1 suffix. See Codex CLI for the full reference.

Because both agents use the same key, they draw from the same prepaid balance. To check spending:

curl https://api.mirapi.ai/api/log/token -H "Authorization: Bearer $MIRAPI_API_KEY"
curl https://api.mirapi.ai/api/usage/token -H "Authorization: Bearer $MIRAPI_API_KEY"

/api/log/token lists per-request rows; /api/usage/token returns account-level totals. Text is metered per token (input / output / cache read), reasoning tokens bill as output, and prompt caching is enabled automatically on OpenAI-compatible models. Reconcile against the Platform billing log (https://platform.mirapi.ai).

Error handling

Status	Meaning	What to do
401	Key missing, invalid, or unknown	Check the exported key
403	Key valid but refused (balance, whitelist, quota, or IP)	Fix the cause, then retry
413	Payload too large	Trim the diff sent to the model
429	Rate limited	Jittered exponential backoff (1s→2s→4s, cap ~30s); no `Retry-After` header
500	Gateway or upstream error	Idempotent requests can be retried safely

The gateway does not retry for you. Every error message ends with a MirAPI request ID; include it in support tickets.

Pitfalls

Hook stdout is shown to Claude Code, so keep the script silent except for the verdict.
The review runs inside the hook, so a long diff delays the next turn; keep the timeout tight and the prompt concise.
git diff HEAD --stat covers staged and unstaged changes but not untracked files; add git add -N . (or switch to git status --porcelain) if new files matter.
If Codex is not logged in or misconfigured, the script exits quietly (|| true). Test it on its own first.

Approximate cost

Each review is one short Codex turn, typically a few thousand tokens. That costs anywhere from a fraction of a cent to a few cents, depending on the diff size and the model. Exact amounts show up in the Platform usage log and GET /api/log/token.