Codex in VS Code: A Careful First Setup

A careful Codex setup starts with a small workspace, a clear authentication choice, and permissions you understand. This walkthrough takes you from installing the VS Code extension to reviewing a first change. It also explains where a relay connection needs extra verification, because a working API key alone does not prove that every Codex feature will work.

Step one: Open a small trusted workspace

Start with a repository you know and a task you can check easily. Commit existing work or save a clean checkpoint before letting an agent edit files. Avoid using a directory that contains unrelated projects, credentials, or personal documents as your first workspace.

Review the repository’s setup instructions and any AGENTS.md files, which can provide instructions that Codex follows. Identify one inexpensive validation command, such as a focused test or a lint check. This gives your first session a concrete success condition.

Step two: Install the official Codex extension

Find the official Codex extension in the VS Code marketplace and verify that its publisher is OpenAI before installing it. Open its panel and follow the authentication choices offered by your installed version. Interface labels and available settings can change, so use the extension’s current documentation when an option differs.

If you work through WSL, SSH, or a development container, establish where the extension and its agent process run. Configuration files and environment variables must be available in that environment. A key defined on your laptop may be unavailable inside a container or remote host.

Step three: Choose and verify your authentication route

For the simplest initial check, use the supported OpenAI sign-in flow if it fits your account and requirements. If you intend to use an API relay, confirm that your installed Codex version supports custom providers and that the relay supports the API protocol Codex requires.

BestRelay, this article’s publisher, provides an alternative API route. It forwards each request to the official model named in that request without substitution. Create a BestRelay account if you want to try this route.

Its API base is https://api.bestapirelay.com. Before configuring Codex, verify the complete endpoint expected by the integration, including whether a version suffix is required. Also confirm Responses API compatibility; support for an OpenAI SDK or another coding client does not by itself establish compatibility with every Codex operation.

Step four: Configure provider settings without exposing credentials

Codex commonly uses a config.toml file under its Codex home directory, typically ~/.codex. Check the current configuration reference and back up an existing file before editing it. In VS Code settings, check whether an alternative Codex home or configuration location has been selected.

For a custom provider, the configuration generally needs these pieces:

• A provider entry under model_providers with a unique identifier.
• A base_url containing the verified API endpoint.
• An env_key naming the environment variable that holds your API key.
• A supported wire_api value, typically responses for current Codex integrations.
• A model_provider selection and the exact model identifier supplied by the provider.

Use the provider’s documented identifier rather than guessing an API name from a display label. Keep credentials out of repository files and committed settings. Make the key available to the environment running Codex, then restart that environment if necessary so the process receives it.

Step five: Limit permissions before requesting changes

Begin with the most restrictive practical permission mode. Ask Codex to inspect the repository and explain a proposed change before allowing edits. Where your version exposes separate sandbox and approval controls, review both: filesystem access and permission to execute a command are different decisions.

For the first editing task, allow access only to the intended workspace and review requests for network access or broader execution individually. Avoid unrestricted execution while you are still checking which configuration, account, and provider the extension is using.

Step six: Validate one change and inspect usage

Request one small change, inspect the diff, and run the relevant check. Confirm the selected provider and model in the available session information. If a request fails, check authentication, endpoint formatting, model access, and protocol support before changing unrelated settings.

For relay billing, BestRelay uses pay-as-you-go charges based on provider-reported token counts, with cache reads and writes priced separately. Its broader coverage includes Claude, GPT, Gemini, DeepSeek, Kimi, GLM, Qwen, and Grok, and it works with Claude Code, Codex, Gemini CLI, and OpenAI SDKs. Members also earn a referral commission when invited users top up. Keep those commercial details separate from your technical acceptance check: a successful first setup produces a reviewable change and a passing validation command.