Codex
From glossary entries and tool comparisons to coding agents and local models: every step of putting AI to work, written to be followed.
Series and tutorial hubs
Series to read in order, each with its own directory and learning paths.
Codex learning hub: tutorial directory
A planned 60-lesson, ten-unit Codex curriculum, from setup and your first task to MD instructions and advanced integrations. Find your next lesson by experience, platform, goal or command; unpublished entries show their status.
Lifestyle
Permissions, sandbox, network and keys
Sandbox rules define technical access to files and networks; approval policy determines when the agent asks before acting. No prompt does not guarantee permission, and read access does not imply write access everywhere.
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Integrating parallel work
Integrate independent edits using file and interface contracts, resolve conflicts and verify combined behavior.
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Choose a model, effort and speed
Model choice affects available capabilities and usage conditions; reasoning effort affects how much work the agent devotes to a problem. Compare quality on the same small task before increasing effort. Use the options currently exposed by your account rather than assuming a named model is universally available.
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Continuing Codex work on iPhone or iPad
Check the available iOS entry point, pairing and authentication, then track a supported task on its host.
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Mobile: iPhone and Android
Remote in the ChatGPT mobile app lets you guide Codex work on a connected computer. Official documentation lists iOS and Android clients, with Mac or Windows hosts, subject to rollout. This does not install a full development environment on the phone, and does not establish Linux host support.
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Continuing Codex work on Android
Check the Android app, pairing and notifications, select the correct host and verify the task output.
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MCP setup and connection checks
MCP connects Codex to tools and data. STDIO servers usually start as local processes; HTTP servers use a URL. Saving configuration only proves it exists: verify startup, authentication and an actual tool response.
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MCP connection diagnosis and recovery
Inspect process, transport, authentication and tool discovery, preserve errors and verify a minimal operation.
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Markdown and MD files
Markdown uses plain-text markers for headings, lists, links and code, commonly in .md files. README.md explains a project, AGENTS.md supplies agent instructions and SKILL.md defines a reusable skill. An arbitrary MD file is not automatically an instruction source.
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Workshop: maintaining an existing project
Establish a baseline, implement one change and deliver traceable regression checks and handoff notes.
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JSON output and result validation
Separate event streams from final results, parse structured output and reject missing or invalid fields.
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Implementing the todo filters
Implement Active and Completed filters from start, preserving data and verifying normal and boundary cases.
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Get started in your IDE
IDE integration places Codex beside your code for focused explanation and edits. VS Code, Cursor and Windsurf use the Codex extension; Xcode and JetBrains expose their own integration flows. Do not interchange their installation steps.
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Git, branches, diffs and recovery
Git stores file history, branches organize changes and diffs show what changed. Codex can help, but you must verify that the changes belong to the task. Restoring an old conversation does not restore Git files.
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Lifestyle
Finish your first small project
Use an independent copy of the Small Steps todo website to change its heading and background. Identify the five practice files and compare the diff, core tests and two viewport widths while preserving behavior and data.
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codex exec and scripts
codex exec runs one non-interactive task for scripts or CI. Normally progress goes to stderr and the final answer to stdout. --json produces JSON Lines events, not a single JSON object.
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Desktop: Windows, macOS and Linux
The desktop workspace combines tasks, files, terminals and change review. Current official downloads use the name ChatGPT desktop app; choose Codex inside it. Follow the separate installation path for your system. Linux is a preview with a specific support list, not a promise of compatibility with every distribution.
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A complete debugging workflow
Debugging starts with a reproducible symptom, narrows causes with evidence and verifies the fix. Give the input, exact step, expected behavior and observed failure instead of only saying the site is broken.
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Workshop: build a CSV cleanup tool
Build a CSV cleaner that preserves its input and writes a new output. The exercise trims whitespace, lowercases email, keeps the first valid occurrence of an address and skips blank names or malformed addresses. It reports kept, duplicate and invalid counts. Its format check does not prove a mailbox exists.
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Cross-device handoff: files and environments
Track the conversation, host, directory and branch so a handoff continues the intended work.
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Context and task handoff
Long work needs durable decisions and evidence, not just a long conversation. README explains use, design documents explain choices, handoffs record current progress and AGENTS.md holds ongoing instructions. Do not turn all temporary progress into permanent rules.
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Configuration precedence and diagnosis
Trace ineffective or conflicting settings, change one item at a time and keep a reversible record.
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Configure Codex with config.toml
config.toml sets client options, while AGENTS.md describes working instructions. User settings live in Codex home; trusted projects can add .codex/config.toml. CLI overrides, project layers and managed requirements mean a single file does not prove the effective configuration.
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CLI commands and slash commands
Distinguish shell commands and launch flags, interactive slash commands, keyboard shortcuts and natural-language requests. Check the input location: /plan belongs in the Codex interactive client; codex --help runs in the operating-system terminal.
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