# Codex Advanced usage

> Codex: AGENTS.md, profiles, MCP, non-interactive tasks, approvals and practical workflows.

URL: https://docs.passion8.cc/en/docs/codex/tips
Language: en
Publisher: Passion8

Effective Codex work combines suitable permissions, project context, profiles, MCP and non-interactive execution. See [Commands](https://docs.passion8.cc/en/docs/codex/commands) for a quick reference.

## AGENTS.md project instructions

Place AGENTS.md at the project root to explain conventions, similarly to Claude Code's CLAUDE.md.

```markdown title="AGENTS.md"
# Project conventions

Stack: Python + FastAPI
Package manager: uv, not pip

## Commands
- Start: uv run uvicorn app:main
- Test: uv run pytest

## Style
- Include type annotations.
- Run pytest after changes.
```




Instructions are layered: user preferences in ~/.codex/AGENTS.md, shared repository rules at the root and more specific rules in subdirectories. Use /init to generate a starting draft.




## Advanced config.toml settings

Common settings, with the full setup in [Configuration](https://docs.passion8.cc/en/docs/codex/config):

| Setting | Purpose |
| --- | --- |
| `model` | Default model, as enabled in your provider's catalog |
| `model_reasoning_effort` | A supported effort such as low / medium / high |
| `approval_policy` | on-request / never |
| `sandbox_mode` | read-only / workspace-write / danger-full-access |
| `web_search` | Search mode; live selects current web access where supported |

Override a setting for one run with `-c key=value`, for example `codex -c model_reasoning_effort=high`.

## Switch settings with profiles

Store scenario-specific settings in a profile and select it with `--profile`:

```toml title="~/.codex/fast.config.toml"
# Profile files use top-level keys.
model = "gpt-6-sol"
model_reasoning_effort = "high"
approval_policy = "on-request"
sandbox_mode = "workspace-write"
```

```bash
codex --profile fast "Add tests for this module"
```

Old `[profiles.fast]` examples should be migrated to the separate file. Retired approval values such as on-failure/untrusted should not be copied into new configuration.

## Connect tools with MCP

MCP connects external tools and data such as browsers, databases and internal APIs. Define the server in config.toml:

```toml title="~/.codex/config.toml"
[mcp_servers.my-tool]
command = "npx"
args = ["-y", "@scope/my-mcp-server"]
# env = { API_KEY = "..." }
```

Use `/mcp` to inspect connectivity and available tools.




MCP servers receive the access you give them. Connect trusted sources and scope their permissions.




## Non-interactive scripts and CI

`codex exec` completes a task without entering the interactive TUI:

```bash
# One task
codex exec "Fix lint failures and run the relevant tests"

# Explain a staged diff
git diff --staged | codex exec "Summarize these changes as a commit message"
```

Use explicit, limited permissions for unattended work, such as read-only or a specific writable workspace.

## Approvals and sandbox

Codex combines approval policy with the sandbox boundary:



- [Conservative starting point](https://docs.passion8.cc/): Use on-request with a suitable sandbox for unfamiliar projects.
- [Focused local implementation](https://docs.passion8.cc/): Use workspace-write and scoped approvals for changes within the project.
- [Unrestricted execution](https://docs.passion8.cc/): Bypass flags are for controlled, isolated, recoverable environments only.



`--full-auto` is deprecated. New scripts should use explicit `--sandbox workspace-write --ask-for-approval on-request`. `-a` and `-s` override approval and sandbox settings; `-C` sets the working directory.




Do not use unrestricted execution in unfamiliar repositories, production directories or secret-bearing folders. See [Security](https://docs.passion8.cc/en/docs/security).




## Common workflow







### Understand first

Ask Codex to explain the project's structure and entry points, then verify its understanding.





### Define the goal and plan

Plan complex changes before implementation. Correct the direction here; use /model for supported reasoning adjustments when needed.





### Implement and check

After agreeing on scope, implement the change and run relevant tests/builds.





### Review the diff

Inspect changes with /diff. Keep work under version control so unwanted changes can be reverted selectively.






## Continue reading



- [Commands](https://docs.passion8.cc/en/docs/codex/commands): Slash commands, resume and permissions.
- [Claude Code advanced usage](https://docs.passion8.cc/en/docs/claude-code/tips): Related workflows in another CLI.