Codex CLI Configuration, Explained Line by Line

Start with the settings Codex actually loads

A Codex CLI configuration file controls which model handles your work, how requests reach it, and what the agent may do locally. Understanding those choices helps you avoid both unexpected permissions and unnecessary spending. This walkthrough explains the important lines in a sensible reading order, without asking you to replace your entire configuration.

Codex uses TOML, a format with named settings and grouped tables. Your installed version matters: supported settings and authentication behavior can change. Start with its current configuration reference, and remember that command-line overrides, selected profiles, project settings, and administrator policies can affect the final result.

Read the model and provider choices together

The model setting selects the model identifier sent to the provider. Copy that identifier from your provider’s setup instructions rather than guessing from a display name. If you choose GPT-5.6 Sol from MyRelay’s menu, for example, confirm its exact API identifier and Codex compatibility before using it.

The model_provider setting chooses the connection definition, not another model. Its value must match the identifier of the provider table you intend to use. A mismatch can prevent Codex from finding your connection even when your credentials are correct.

Read these two settings as a pair: one answers “which model?” and the other answers “through which service?” Keeping that distinction clear makes troubleshooting much easier.

Follow the provider table through to authentication

The model_providers table holds custom provider definitions. Each provider has its own identifier, which connects it to the earlier provider selection. In TOML, settings beneath a table header belong to that table until another header changes the context. Accidentally placing a global setting inside a provider table is an easy editing mistake.

Within a provider definition, name supplies a human-readable label. It helps identify the connection, but it does not select the model or authenticate requests.

The base_url setting tells Codex where to send API traffic. For MyRelay, use the precise Codex endpoint documented in its setup instructions. Do not assume that a service’s website address and its API endpoint are interchangeable, or add endpoint suffixes by guesswork.

The env_key setting names the environment variable holding your API key; it is not the secret itself. Keep that secret outside shared configuration and version control. Also check the documented authentication requirements for your provider rather than assuming an existing ChatGPT login will authenticate a relay connection.

The wire_api setting selects the API protocol. Current Codex integrations commonly require the Responses API. An OpenAI-compatible service is not automatically compatible with every Codex feature, so verify the required protocol and tool support before troubleshooting individual requests.

Choose permissions separately from model quality

The approval_policy setting controls when Codex asks for permission. The sandbox_mode setting controls the execution boundary, including whether commands can modify your workspace. They solve different problems: approval is an interaction rule, while sandboxing limits access.

For an unfamiliar project, begin with restricted access and review proposed changes. Broader permissions do not make a model smarter or cheaper. Network access can also have separate controls, so do not assume permission to edit files includes permission to contact external services.

Use reasoning and profiles to limit unnecessary work

The model_reasoning_effort setting adjusts reasoning effort on supported models. Available values depend on the model and provider. Higher effort can increase latency and token consumption, so start with a supported moderate setting and raise it only when a task justifies it.

The profiles table groups alternative settings you can select for different work. A routine profile and a demanding-task profile can reduce repeated editing. Check which profile is active before a long session; a profile can override choices you noticed elsewhere.

Verify one small task before committing a budget

Ask Codex to explain a small function before assigning a repository-wide change. Confirm the selected model, connection, permissions, and resulting usage. With MyRelay, you can inspect each request’s tokens and cost rather than estimating spending from session length alone.

Create a MyRelay account if you want one personal, pay-as-you-go key and budget for your coding tools. Then expand gradually: a working configuration and a measured first request are more useful than an elaborate setup you have not tested.