What Is the CLAUDE.md Equivalent for ChatGPT?
ChatGPT has no CLAUDE.md file. Here are the right places to put project instructions in ChatGPT, and how to keep cross-assistant rules in one place.
Updated 5 min read
CLAUDE.md is specific to Claude Code: a Markdown file that Claude Code reads automatically when it starts a session in your project folder. ChatGPT has no equivalent file format. Instead, ChatGPT offers several places to add persistent instructions depending on which part of the product you are using and how far those instructions should reach.
If you work with both Claude Code and ChatGPT on the same project, tools like fenbs let you keep the project rules, decisions, and context in one place that both assistants can read through an MCP connection — rather than duplicating the instructions in two separate formats. This page explains where instructions live in ChatGPT and how to choose the right place.
Where ChatGPT accepts persistent instructions
ChatGPT offers three main places for persistent instructions, each with different scope. Understanding the scope is the key to choosing correctly — instructions that apply to every conversation should not live in a project-specific location, and project-specific rules should not clutter account-level settings.
| Location | Scope | Best for |
|---|---|---|
| Custom Instructions (Settings) | All conversations for that account | Style preferences, background facts about yourself, how you want responses formatted |
| Project Instructions (ChatGPT Projects) | All conversations in that Project | Context about a specific project: its goal, relevant facts, constraints, how you want answers structured |
| System prompt in ChatGPT Work / API | That specific deployment or API call | Operator-level rules for a particular use case or integration |
| Conversation context | That conversation only | Session-specific context that does not need to persist beyond the chat |
Custom Instructions: the account-level setting
Custom Instructions let you tell ChatGPT two things: information about yourself that is useful across all conversations, and how you want it to respond. You can find them at Settings → Personalization → Custom Instructions. They apply to every chat you start, making them the right place for stable preferences — your preferred output format, your technical level, your professional context.
These are not a replacement for CLAUDE.md. They do not accept a file, they apply account-wide rather than per-project, and they have a character limit. Project-specific rules — the naming conventions for this codebase, the command to run tests, the decision not to use a particular library — do not belong here. See ChatGPT's help page (opens in a new tab) for current details on the feature.
Project Instructions: the closest equivalent
ChatGPT Projects let you create a named project that retains files and instructions across conversations. The project instructions apply to every conversation you start inside that project, which makes them the closest structural equivalent to a CLAUDE.md for a specific body of work.
You can write project instructions as plain text, upload files for reference, and start multiple conversations that all read the same context. The scope is intentional: instructions here do not affect other projects or new conversations outside the project. For coding work, the compare Claude Projects vs ChatGPT Projects guide covers the differences in detail.
What CLAUDE.md can do that ChatGPT cannot match exactly
CLAUDE.md has one capability that ChatGPT project instructions do not: it is a file in your repository that Claude Code reads automatically from the file system, without you opening a browser or updating a settings panel. When the instructions change, you commit the change to git and every session picks it up. Team members get the same instructions by checking out the branch.
ChatGPT project instructions are stored in ChatGPT's systems. They are not in your repository, they do not version with your code, and team members need their own ChatGPT accounts to access a project. This is a genuine structural difference, not just a format difference.
Keeping rules consistent across assistants
If your team uses both Claude Code and ChatGPT on the same project, maintaining the same set of rules in two separate places is fragile. The rules drift, someone updates one and not the other, and an assistant acts on a stale constraint. One solution is to keep the authoritative rules in fenbs and connect both assistants to the same project over MCP.
A Claude Code session reads the fenbs project context — its rules, decisions, and current tasks — at the start of a session. A ChatGPT conversation with the fenbs MCP connection does the same. Both see the same Decisions and rules, the same Where we left off, and the same open tasks. Each assistant still has its own instruction file or settings, but the shared facts live in one place.
Keep project rules where both Claude and ChatGPT can read them
Add your project's rules, decisions, and approved templates to fenbs. Connect Claude Code and ChatGPT over MCP from Integrations, and both assistants read the same context at the start of each session. You update the rules once, in one place, and both see the change.
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How to do this with fenbs
- Create a free account. Start a project and add the rules and decisions that should apply regardless of which assistant handles the work.
- Write a CLAUDE.md for Claude Code that covers the file-system facts: commands, folder structure, and constraints that belong in the repo.
- Write ChatGPT project instructions for the conversational context ChatGPT needs: your preferred format, the project goal, and a short description of what is in fenbs.
- Connect both assistants to fenbs from Integrations and ask each to read the project context at the start of a session.
- When a project rule changes, update it in fenbs. Both assistants see the change the next time they read the context.
For a comparison of Claude and ChatGPT on coding work, see Claude vs ChatGPT for coding. For moving a project from one assistant to the other, see the switching guide.