Yes, ChatGPT can read .md files. Upload one in a chat and it reads the markdown as plain text, headings, lists and links included. What it can't do from chatgpt.com is change the file on your disk: you copy its answer back yourself. For that you need OpenAI's Codex agent working on the folder, which is where the editors below differ.
"ChatGPT-compatible" means three different things depending on the editor: copy-pasting text in and out of chatgpt.com, calling OpenAI's API under the hood, or running OpenAI's own agent against your files directly. Ritemark is the only markdown editor here with OpenAI's Codex agent built into its AI sidebar: sign in with your ChatGPT account and a GPT model edits your .md files in place, with nothing to install. VS Code gets there too, through Codex CLI in its terminal. The ChatGPT desktop app can now work on local folders too, through its Codex mode and local projects, but it's an assistant with the conversation in the middle, not a markdown editor. GitHub Copilot and Notion AI both use GPT-class models but aren't ChatGPT itself.
Here's how each option actually connects to OpenAI's models, and what that means for editing markdown.
1. Ritemark + Codex
Best for: Writers who want a GPT model editing markdown files directly, with no copy-paste
Codex, the open-source coding agent OpenAI ships alongside ChatGPT, is built into Ritemark's AI sidebar, so there is nothing to install. It reads, edits, and saves your .md files, and you can switch to Claude Code or OpenCode in the same conversation, with no browser tab and no pasting text back and forth.
Pricing: Ritemark is free. In Ritemark, Codex signs in with your ChatGPT account. To pay per token with your own OpenAI API key, choose OpenCode instead. OpenAI includes Codex in every ChatGPT plan, the free one with tighter limits.
File access: Direct. Codex reads and edits the files in your folder from the AI sidebar.
2. ChatGPT desktop app + any editor
Best for: People who want one assistant for chat, research and tasks across their apps, and a separate editor for the writing
Since July 2026 the ChatGPT app for Mac and Windows has three modes: Chat, Work and Codex. Chat is the assistant you know, and it still has Canvas, a split-screen workspace whose documents download as Markdown, PDF or Word. Work is an agent for longer tasks that uses your files, apps and websites. Codex is OpenAI's coding agent, and a local project can point it at a folder on your computer, where it reads and edits files the same way Codex does anywhere else.
So the desktop app does reach your disk now. What it doesn't give you is a markdown editor: the conversation sits in the middle of the window, and you open the .md file somewhere else to read and polish it. Our ChatGPT Desktop comparison goes into the differences, including why a Ritemark window belongs to one folder and its setup.
Pricing: Free tier available. Plus is $20/month, Pro is $200/month, with Business and Enterprise tiers for teams. Codex is included in every plan, the free one with tighter limits.
File access: Direct in Codex mode and Work, on the folders you connect. Chat and Canvas work on text inside the conversation and export a file.
3. VS Code + GitHub Copilot or Codex CLI
Best for: Developers who want GPT models inside a familiar IDE
VS Code reaches OpenAI's models two ways. GitHub Copilot's chat and agent mode can be pointed at OpenAI models alongside its other options. Separately, Codex CLI runs in VS Code's built-in terminal, with direct file access.
Pricing: VS Code is free. GitHub Copilot has a free tier (2,000 completions/month), Pro at $10/month, Pro+ at $39/month, and Business at $19/user/month. Codex CLI in the terminal uses your ChatGPT plan or an OpenAI API key.
File access: Direct, when using Codex CLI in the terminal. Copilot's chat panel edits files through its own suggestion/apply flow rather than a raw terminal agent.
4. Notion AI
Best for: Teams who want GPT-assisted docs without leaving Notion
Notion AI is bundled into Notion's Business plan and can route requests to GPT-5-class models alongside Claude and Gemini, picked automatically or by hand from a model list. It's a genuine way to get GPT output inside a markdown-flavored document, but it isn't ChatGPT. There's no chatgpt.com account involved, and documents live in Notion's own database, not as .md files on disk.
Pricing: Business plan runs about $20/user/month billed annually. Free and Plus plans get a limited number of lifetime AI responses before AI features stop working.
File access: None in the local-file sense. Notion AI edits Notion pages, not files a terminal agent could open directly; export to markdown is a manual step.
Comparison Table
| Tool | Integration Method | File Access | Copy-Paste Required? | Price |
|---|---|---|---|---|
| Ritemark | Codex built into the AI sidebar (or OpenCode with an OpenAI key) | Direct, on-disk .md files |
No | Free + ChatGPT plan or API cost |
| ChatGPT desktop app | Codex mode and Work on connected folders; Canvas export in Chat | Direct in Codex and Work; export only in Chat | No for Codex; you still need an editor to read the file | Free, Plus $20/mo, Pro $200/mo |
| VS Code | Codex CLI in terminal, or GitHub Copilot | Direct via Codex CLI; suggestion-based via Copilot | No (Codex CLI) / Partial (Copilot) | Free + Copilot $10-$39/mo or Codex CLI cost |
| Notion AI | Multi-model routing (GPT-5-class + others) | None (edits Notion pages, not files) | Yes, for use outside Notion | ~$20/user/mo (Business) |
"ChatGPT the Product" vs. "GPT-Powered"
Most tools that mention OpenAI aren't actually ChatGPT. They call OpenAI's API to run a GPT-class model behind their own interface. Notion AI and GitHub Copilot both work this way: real GPT output, no chatgpt.com account, no Canvas, no ChatGPT subscription required for that specific feature. Codex CLI sits in a different category. It's OpenAI's own agent, included in every ChatGPT plan, which makes it the most literal sense of "ChatGPT-compatible" among terminal tools. The same account that logs into chatgpt.com also authenticates the agent editing your files. Ritemark builds that agent into its AI sidebar, and VS Code gives it a terminal to run in; the difference between them is everything else in the editor around it.
How to Choose
If you want a GPT model editing markdown files directly with no copy-paste, Ritemark (Codex in its AI sidebar) and VS Code (Codex CLI in its terminal) both get there, so pick based on whether you want a writing-first app or a code-first IDE around it. If you want one assistant for conversation, research and tasks across your cloud apps, the ChatGPT desktop app covers that, and its Codex mode can edit files in a folder you connect, though you'll open them in another app to read and polish them. If your team already lives in Notion, Notion AI adds GPT-class assistance to existing pages without a separate ChatGPT account, though it can't touch files outside Notion. If you're a developer who wants an IDE-native assistant rather than a terminal agent, GitHub Copilot on top of VS Code is the more polished, if pricier, path to GPT-backed suggestions.
To see how Codex compares with the other agents in Ritemark, read the best markdown editor for AI workflows guide or the AI agent setup guide.
Frequently Asked Questions
Can I use ChatGPT to edit markdown files directly?
Yes, through Codex. It comes with every ChatGPT plan and edits files in a folder directly: in the ChatGPT desktop app's Codex mode with a local project, built into Ritemark's AI sidebar, or as Codex CLI in VS Code's terminal. The chat itself, on chatgpt.com or in the app's Chat mode, works on text in the conversation, and Canvas exports a .md file rather than editing one on your disk.
Does Ritemark support OpenAI's GPT models?
Yes. OpenAI's models are available through Codex in the AI sidebar with your ChatGPT account, or through OpenCode with your own OpenAI API key. The model list updates on its own, so the exact models change over time.
Does VS Code support ChatGPT or GPT models?
Yes, two ways: GitHub Copilot can use OpenAI models in its chat and agent mode, and Codex CLI runs in VS Code's integrated terminal, with direct file access.
Does Notion AI use ChatGPT?
Not literally. Notion AI's Business plan routes requests across several frontier models, including GPT-5-class ones, Claude, and Gemini. That's real GPT output, but no chatgpt.com account or ChatGPT-branded interface involved.
What's the difference between "ChatGPT-compatible" and "GPT-powered"?
"GPT-powered" usually means a tool calls OpenAI's API to run a GPT model behind its own interface, with no ChatGPT account needed. That's Notion AI and GitHub Copilot's OpenAI option. "ChatGPT-compatible" in the strictest sense means the same ChatGPT subscription authenticates the tool, which is true of Codex CLI specifically.
Which ChatGPT plan do I need for Codex CLI?
Any of them. OpenAI includes Codex in every ChatGPT plan, Free included with tighter limits, or you can use your own OpenAI API key billed separately. Codex CLI itself is free, open-source software either way. Inside Ritemark, Codex signs in with your ChatGPT account; to use an OpenAI API key there, choose OpenCode.
Can I export a ChatGPT Canvas document as markdown?
Yes. A finished Canvas document downloads as .md, PDF, or Word, depending on what you pick from the export menu.
Is Codex CLI free?
The software is free and open source. Usage draws down your ChatGPT plan's included quota, or bills per token if you authenticate with your own OpenAI API key instead.
Which of these tools edits markdown files with no copy-pasting?
Ritemark, through Codex (or Claude Code or OpenCode) in its AI sidebar, VS Code when you run Codex CLI in its integrated terminal, and the ChatGPT desktop app in Codex mode. All three give the agent direct read/write access to files on disk. Ritemark is the one where the document you're writing sits in the same window as the agent.
Does GitHub Copilot cost extra on top of a ChatGPT subscription?
Yes. Copilot is billed separately from ChatGPT. A Copilot Pro seat costs $10/month on its own, regardless of whether you also pay for ChatGPT Plus.
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