Connect ChatGPT to an external memory: the MCP server, step by step

Updated 30 October 2026. Steps taken from OpenAI's official documentation, read on 30 October 2026. OpenAI often renames and moves these menus: if a label has changed, the principle stays the same.

To connect ChatGPT to an external memory, add its MCP server as a plugin: on chatgpt.com, open Plugins, click “+” then Add custom MCP server, enter a name and the server URL, choose OAuth authentication, review the warning, then click Create as a plugin. In a chat, type @ and pick the plugin. It is done on the web, with a paid plan that decides your rights (read-only, or read and write).

If you first want to sort out ChatGPT's built-in memory, here is how to turn it on and clear it when it's full.

This guide uses Pryzm Memory as the example: a persistent memory shared across several AIs over MCP. The steps are the same for any remote MCP server; only the name and the URL change. Source: OpenAI's guide to custom MCP servers.

What you need before you start

• ChatGPT on the web (chatgpt.com): that is where OpenAI says to add a custom MCP server.
• A plan that allows it. Per OpenAI's help centre, full MCP access (read and write) is limited to Business, Enterprise and Edu; on Pro, a custom MCP server can be connected read-only. The help page doesn't mention the free plan or Plus: check on your account.
• On a workspace (Business, Enterprise, Edu), the permissions set by your admins apply: if the option is missing, ask them.
• The MCP server URL. For Pryzm: https://pryzm-memory.com/mcp.
• An account with the memory service. Pryzm is free up to 100 memories; on the free plan, your email must be confirmed before you connect an AI.

Read-only has a concrete consequence: ChatGPT can search Pryzm for what Claude, Cursor or another AI saved, but cannot save to it itself. Plans and rights are summarised in OpenAI's help centre.

The steps in ChatGPT

1. Open Plugins on chatgpt.com.
2. Add a server. Click “+”, then Add custom MCP server.
3. Name it. For example “Pryzm Memory”. The description is optional.
4. Enter the address. Under Connection, enter the server URL: https://pryzm-memory.com/mcp.
5. Choose OAuth as the authentication.
6. Review the risk warning, then click Create as a plugin.
7. Sign in to the service. For Pryzm, enter your Pryzm username (the one you picked at sign-up, not your email) and password. ChatGPT receives its own access token.

To use it, type @ in the prompt box and pick the plugin, then ask: “@Pryzm Memory, what do you know about my current projects?” OpenAI recommends being explicit about which tool to use. Write actions, such as saving a memory, require confirmation by default: review the text being sent, then accept.

Older interface. If you don't see “Plugins”, your account may still show the older path: Settings → Apps → Advanced settings → Developer mode, then create an app with the server URL and OAuth authentication.

Get ChatGPT to check the memory without asking every time

A connected app only helps if ChatGPT thinks of using it. To make it check on its own, add an instruction to its custom instructions:

1. Open Settings → Personalization → Custom instructions (web and desktop app).
2. Paste an instruction telling ChatGPT to check the memory at the start of every conversation and before answering anything that depends on your context, then to save what's worth keeping.
3. Save. Per OpenAI, the change applies immediately to all chats.

For Pryzm, the ready-to-paste text is on the connection page, in the “main memory” section. It fits within the 5,000-character limit that OpenAI's help centre gives for paid plans.

Limits worth knowing

• Web and paid plans. A memory filled from another AI is still readable by ChatGPT as soon as it is connected, even read-only.
• Rights depend on the plan. Read-only (Pro, per OpenAI) means ChatGPT cannot save a memory.
• Write confirmations. ChatGPT asks for your approval before any action that changes data. That's intended: you stay in control.
• You are responsible for the server you plug in. A custom MCP server is not an app from ChatGPT's catalogue: only connect servers whose publisher you know.

What does the memory server see?

The server receives what ChatGPT sends it when it calls a tool: a search query, or the text of a memory to save. It does not receive your full conversation history.

At Pryzm, servers are in Germany and each account is encrypted with its own key (AES-256-GCM). One limit to know: during a session, the server decrypts your memories in memory so it can search them. It is not end-to-end encryption. A message starting with ## is never saved.

If something doesn't work

• No “Add custom MCP server”: your plan doesn't include it, or your workspace admin hasn't allowed it.
• ChatGPT reads but won't save: your plan is read-only. Save from Claude or another connected AI; ChatGPT will find it.
• “Incorrect username or password” on the Pryzm page: use your Pryzm username, not your email.
• The sign-in window doesn't open: allow pop-ups for chatgpt.com, then try again.
• ChatGPT answers without checking the memory: call the plugin with @, and check that your custom instructions are saved.

When it isn't useful

If you only use ChatGPT, its built-in memory is probably enough. An external memory makes sense when you also work with Claude, Claude Code, Perplexity, Cursor or Gemini CLI, and want them to share the same context instead of explaining it to each one.

To check in two minutes that your AIs really share one memory, run the Claude → ChatGPT test. Guides for other AIs are on the connection page; for Claude, see how to add a custom connector.