codex-cursor

Local OpenAI-compatible HTTP proxy that lets Cursor (or anything else that speaks the OpenAI Chat Completions API) consume your ChatGPT/Codex subscription instead of a metered OpenAI API key.

It reuses the access tokens that the codex CLI stores in ~/.codex/auth.json and translates Cursor's /v1/chat/completions traffic to the ChatGPT backend's Responses API.

Calls a private ChatGPT/Codex backend with the same credentials and limits as the codex CLI. Personal use only.

Prerequisites

1. bun installed.
2. The codex CLI installed and signed in (codex login), so ~/.codex/auth.json exists.

Run it

# one-shot, no install:
bunx codex-cursor --api-key "$(openssl rand -hex 16)"

# or from a clone:
bun install
bun run src/index.ts --api-key "$(openssl rand -hex 16)"

Flags / env vars:

| Flag | Env var | Default | | ------------------------ | ----------------------------- | --------------------- | | --host <addr> | CODEX_SUB_HOST | 127.0.0.1 | | --port <n> | CODEX_SUB_PORT | 4141 | | --api-key <secret> | CODEX_SUB_API_KEY | no auth required | | --auth-path <path> | CODEX_SUB_AUTH_PATH | ~/.codex/auth.json | | --reasoning-effort lvl | CODEX_SUB_REASONING_EFFORT | xhigh (minimal, low, medium, high, xhigh) | | --quiet / --verbose / --log-level lvl | CODEX_SUB_LOG_LEVEL | info (quiet, info, verbose) |

Always set --api-key when exposing the proxy via a tunnel — the public URL is otherwise an open Codex-subscription faucet.

Expose it to Cursor

Cursor's chat runs on Cursor's cloud backend, which calls your custom base URL. It refuses private addresses, so http://127.0.0.1:4141/v1 will fail with Access to private networks is forbidden.

Use a Cloudflare quick tunnel:

brew install cloudflared

# terminal A:
bunx codex-cursor --api-key "$(openssl rand -hex 16)"

# terminal B:
cloudflared tunnel --url http://127.0.0.1:4141

cloudflared prints a https://random-words.trycloudflare.com URL.

Point Cursor at it

1. Cursor → Settings → Models → "OpenAI API Key" panel
2. Toggle Override OpenAI Base URL and set:
   • Base URL: https://<your-tunnel>.trycloudflare.com/v1
   • API Key: the hex string you passed to --api-key.
3. Click Verify.
4. In the model picker, add a custom model. Working slugs: gpt-5.5, gpt-5.4, gpt-5.4-mini, gpt-5.3-codex, gpt-5.3-codex-spark. The exact list is returned by GET /v1/models.

Caveats

• The proxy issues stateless single-turn calls; Cursor's full history is sent every time.
• If codex logout invalidates your refresh token, the proxy fails with refresh_token_expired until you codex login again.