When to Use ChatGPT vs Codex: Exploring the New Era of AI Agents

If you use ChatGPT, Claude, Claude Code, or Codex and wonder which tool fits a particular task, this article walks through OpenAI's Agent tool and breaks down Codex's seven core capabilities with real‑world examples.

Ability 1: Full File Access

Codex stores all files on your computer, unlike ChatGPT or Claude which keep files in the cloud. This local access lets Codex create dynamic videos, landing pages, games, desktop apps, Excel/Word documents with charts, and presentations that can be exported to Canva.

Real example – automatically processing 60 receipts : The author placed 60 receipt photos in a folder, asked Codex to analyze them and generate an Excel dashboard. Within seven minutes Codex performed OCR on 53 receipts, classified transactions, and produced a workbook showing total spend, category breakdowns, payment‑method summaries, and a monthly trend chart.

Project organization: Files are kept in a Project folder, which links a conversation to a specific directory. Two ways to start a conversation exist – a simple Chat that appears in the sidebar, or a Project that ties the dialogue to a folder. The author stores all projects under Documents for easy management.

Ability 2: Persistent Memory

Codex maintains two kinds of memory. Manual memory is stored in agents.md; when you tell the Agent to remember a preference (e.g., a landing‑page style), the instruction is written to this file. Automatic memory lives in the memories folder and records every task the Agent performs; it should not be edited manually.

Ability 3: Plugin Ecosystem

More than 100 plugins can be invoked with the @ symbol, connecting Codex to external tools such as Gmail, Notion, Slack, and many others.

Real example – analyzing brand‑deal emails : The author created a Project called “Brand Deals”, asked Codex to scan recent Gmail messages for paid‑promotion offers, and to compile the findings into a Markdown table with notes. Codex fetched the emails, generated the table, and even drafted reply messages.

Ability 4: Skill System

Skills are reusable instruction files stored in the plugins/Skill directory. Two creation methods exist:

Prompt‑to‑skill : Directly ask the Agent to create a skill (quick but lower quality).

Manual workflow (recommended) : Let the Agent perform a task, iterate until the output is satisfactory, then ask it to save the process as a skill.

Example: after refining a brand‑deal research workflow, the author saved it as brand deal researcher.skill.md. The skill can be invoked with a slash command, and it can include plugin calls.

Ability 5: Built‑in GPT‑Image 2

Codex includes the world‑leading image‑generation model. The author created a Project “content”, supplied a sweater photo, and instructed Codex to generate five product images featuring models of different nationalities (1, 3, and 5 people per image). The model produced high‑quality images that were saved directly in the project folder.

Ability 6: Browser and Computer Control

Codex can control both the desktop and the browser.

Real example 1 – automatic Canva presentation : Using the @computer use plugin, the author asked Codex to open Canva, create a new presentation, and place each of the five generated images on separate slides. Codex moved the mouse, performed the clicks, and completed the presentation without any manual input.

Real example 2 – automated web‑app testing : The author created a web app, then said “test the interface using @browser use ”. Codex opened the app in a browser, clicked buttons, navigated pages, and verified that all UI elements worked, fully automating the test.

Ability 7: Automation

Any task can be turned into a scheduled automation. The author scheduled the previously created brand‑deal research skill to run every Friday at 9 am, automatically updating the spreadsheet with new email data.

New Feature: Chronicle (screen‑monitoring)

Chronicle continuously records the screen, providing contextual awareness. When the author opened a presentation and asked Codex to suggest additional slides, Chronicle supplied recent screenshots, and Codex proposed a set of slides—including a Codex super‑app map, a control‑loop diagram, and a rationale for choosing Codex over other tools. The feature is powerful but invasive, as it records the screen continuously.

In summary, Codex is not a “better ChatGPT”. ChatGPT remains a cloud‑based conversational assistant, while Codex is a localized Agent super‑app capable of direct file manipulation, reusable workflows, and full computer control. Use ChatGPT for occasional queries; use Codex when you need to process local files, build repeatable processes, or let AI act on your computer.