---
title: Codex
description: "Add persistent memory to OpenAI Codex with the Mem0 plugin — MCP server, memory protocol skill, and plugin marketplace support."
---

Add persistent memory to [**OpenAI Codex**](https://openai.com/index/codex/) with the Mem0 plugin. Codex forgets everything between tasks — this plugin fixes that by connecting to Mem0's cloud memory layer via MCP and using a skill-based memory protocol to automatically retrieve context and store learnings.

## Overview

1. **MCP Server** — Connect to Mem0's remote MCP server for memory tools (add, search, update, delete)
2. **Memory Protocol Skill** — Instructs the agent to retrieve memories at task start, store learnings on completion, and capture session state before context loss
3. **Plugin Marketplace** — Install via Codex's repo-level or personal plugin marketplace
4. **Zero local dependencies** — Cloud-hosted MCP server, no local setup required

## Prerequisites

Before setting up Mem0 with Codex, ensure you have:

1. A Mem0 Platform account and API key:
   - <a href="https://app.mem0.ai?utm_source=oss&utm_medium=integration-codex" rel="nofollow">Sign up at app.mem0.ai</a>
   - <a href="https://app.mem0.ai/dashboard/api-keys?utm_source=oss&utm_medium=integration-codex" rel="nofollow">Get your API key</a> (starts with `m0-`)

2. OpenAI Codex access

3. Your API key exported in your shell:

```bash
export MEM0_API_KEY="m0-your-api-key"
```

## Installation

### Option A — Direct MCP (Recommended)

The fastest way to connect Codex to Mem0 — no downloads, no marketplace. Codex reads MCP servers from `~/.codex/config.toml` as TOML. Add:

```toml
[mcp_servers.mem0]
url = "https://mcp.mem0.ai/mcp"
bearer_token_env_var = "MEM0_API_KEY"
```

Make sure `MEM0_API_KEY` is exported in the shell you launch Codex from, then restart Codex.

<Info>
  Codex's `codex mcp add` CLI only supports stdio MCP servers. Because Mem0's MCP is HTTP/streamable, you configure it by editing `config.toml` directly (or via the **Plugins → Connect to a custom MCP → Streamable HTTP** UI in the Codex app).
</Info>

### Option B — Sideload the Plugin (Advanced)

For the full plugin experience — MCP server **plus** the Mem0 SDK skill, memory protocol skill, and opt-in lifecycle hooks — sideload the plugin from a local clone. The Mem0 repo already ships a marketplace manifest at [`.agents/plugins/marketplace.json`](https://github.com/mem0ai/mem0/blob/main/.agents/plugins/marketplace.json), so there's no JSON to author by hand. This follows the Codex [build-plugins](https://developers.openai.com/codex/plugins/build) local-testing workflow.

<Info>
  Don't combine Option B with Option A. The plugin manifest declares its MCP server via [`.codex-mcp.json`](https://github.com/mem0ai/mem0/blob/main/mem0-plugin/.codex-mcp.json), so Codex auto-registers the `mem0` MCP server when the plugin loads. Adding the same `[mcp_servers.mem0]` block to `~/.codex/config.toml` will create a duplicate registration.
</Info>

**Step 1.** Clone the Mem0 repository anywhere on disk:

```bash
git clone https://github.com/mem0ai/mem0.git ~/codex-plugins/mem0-source
```

**Step 2.** Register the bundled marketplace with Codex's CLI:

```bash
codex plugin marketplace add ~/codex-plugins/mem0-source
```

This points Codex at the repo's `.agents/plugins/marketplace.json`. The bundled file uses `path: "./mem0-plugin"`, which Codex resolves relative to the clone root.

<Info>
  **Why we recommend this over hand-authoring `~/.agents/plugins/marketplace.json`:** Codex requires `source.path` in any marketplace manifest to be **relative** (starting with `./`) and **inside the marketplace root**. The repo's bundled manifest already satisfies this — the marketplace root is the clone directory, and `mem0-plugin/` lives inside it. With a personal `~/.agents/plugins/marketplace.json`, the root is `~/` and the clone has to live under `~/` too. The CLI form sidesteps that constraint.
</Info>

**Step 3.** Restart Codex, run `/plugins`, browse the `Mem0 Plugins` marketplace, and install **Mem0**.

**Step 4 (optional) — enable lifecycle hooks.** Codex doesn't auto-wire hooks from plugin manifests; it only reads them from `~/.codex/hooks.json` (or `<repo>/.codex/hooks.json`). Run the bundled installer once to merge the Mem0 entries into your global hooks file:

```bash
python3 ~/codex-plugins/mem0-source/mem0-plugin/scripts/install_codex_hooks.py
```

Then enable the hooks feature flag in `~/.codex/config.toml`:

```toml
[features]
codex_hooks = true
```

Restart Codex. The installer registers three hooks pointing at scripts inside your clone:

| Event | Behavior |
|-------|----------|
| `SessionStart` | Loads prior memories as bootstrap context |
| `UserPromptSubmit` | Injects relevant memories before each prompt |
| `Stop` | Reminds the agent to persist learnings at turn end |

Re-running the installer is idempotent. To remove the hooks: `python3 ~/codex-plugins/mem0-source/mem0-plugin/scripts/install_codex_hooks.py --uninstall`.

<Warning>
  The hooks file stores absolute paths into your clone (e.g. `~/codex-plugins/mem0-source/mem0-plugin/scripts/...`). If you move or delete the clone, the hooks will break silently — re-run the installer from the new location, or run `--uninstall` first.
</Warning>

### Managing the Plugin

Codex provides CLI commands for managing marketplaces after install:

```bash
codex plugin marketplace upgrade               # pull latest plugin versions
codex plugin marketplace remove mem0-plugins   # unregister the marketplace
```

To pull updates to the plugin source itself, `git pull` inside your clone (`~/codex-plugins/mem0-source`) and then run `codex plugin marketplace upgrade` to refresh Codex's plugin cache. Plugins are cached at `~/.codex/plugins/cache/<marketplace>/<plugin>/<version>/`.

<Info icon="check">
  After either option, start a new Codex task and ask: *"List my mem0 entities"* or *"Search my memories for hello"*. If the `mem0` tools appear and respond, you're all set.
</Info>

## What's Included

| Component | Sideloaded Plugin | Direct MCP |
|-----------|:-----------------:|:----------:|
| MCP Server (9 memory tools) | Yes | Yes |
| Memory Protocol Skill | Yes | No |
| Mem0 SDK Skill | Yes | No |
| Lifecycle Hooks (opt-in) | Yes | No |

## Available MCP Tools

Once installed, the following tools are available in every Codex session:

| Tool | Description |
|------|-------------|
| `add_memory` | Save text or conversation history for a user/agent |
| `search_memories` | Semantic search across memories with filters |
| `get_memories` | List memories with filters and pagination |
| `get_memory` | Retrieve a specific memory by ID |
| `update_memory` | Overwrite a memory's text by ID |
| `delete_memory` | Delete a single memory by ID |
| `delete_all_memories` | Bulk delete all memories in scope |
| `delete_entities` | Delete a user/agent/app/run entity and its memories |
| `list_entities` | List users/agents/apps/runs stored in Mem0 |

## Memory Protocol Skill

When the plugin is sideloaded, the memory protocol skill instructs the agent to:

### On Every New Task
1. Call `search_memories` with a query related to the current task to load relevant context
2. Review returned memories to understand what was learned in prior sessions
3. Optionally call `get_memories` to browse all stored memories

### After Completing Significant Work
Store key learnings using `add_memory` with structured metadata:

| What to store | Metadata type |
|--------------|---------------|
| Architectural decisions | `{"type": "decision"}` |
| Strategies that worked | `{"type": "task_learning"}` |
| Failed approaches | `{"type": "anti_pattern"}` |
| User preferences observed | `{"type": "user_preference"}` |
| Environment discoveries | `{"type": "environmental"}` |
| Conventions established | `{"type": "convention"}` |

### Before Losing Context
Store a comprehensive session summary including goals, accomplishments, decisions, files modified, and current state with metadata `{"type": "session_state"}`.

## Plugin Manifest

The Codex plugin manifest (`.codex-plugin/plugin.json`) follows the Codex plugin specification:

```json
{
  "name": "mem0",
  "version": "0.1.0",
  "description": "Mem0 memory layer for AI applications.",
  "skills": "./skills/",
  "mcpServers": "./.codex-mcp.json",
  "interface": {
    "displayName": "Mem0",
    "shortDescription": "Persistent memory layer for AI coding workflows",
    "category": "Productivity",
    "capabilities": ["Read", "Write"]
  }
}
```

## Example Workflow

```text
# Task 1: Setting up a new service
You: Create a REST API for the notifications service using Express and TypeScript.

# Codex searches memories, finds user preferences from prior tasks.
# After completing the task, Mem0 stores:
#   - Decision: "Notifications service uses Express + TypeScript + Zod validation"
#   - Convention: "All API routes follow /api/v1/{resource} pattern"
#   - Preference: "User prefers explicit error types over generic catch-all"

# Task 2 (days later): Extending the service
You: Add WebSocket support for real-time notification delivery.

# Codex searches memories, retrieves the architecture decisions and conventions.
# Follows the same patterns established in the first task.
```

## Troubleshooting

- **"Connection failed"** — Verify `MEM0_API_KEY` is set in your shell: `echo $MEM0_API_KEY`
- **No tools appearing** — Restart your Codex session after plugin installation
- **Duplicate `mem0` MCP server / "tool collision" errors** — You combined Option A (Direct MCP) with Option B (sideload). The sideloaded plugin auto-registers `mem0` from `.codex-mcp.json`, so remove the `[mcp_servers.mem0]` block from `~/.codex/config.toml`.
- **`plugin/read failed in TUI`** — Codex can't find the plugin directory the marketplace points at. If you used `codex plugin marketplace add <path>`, confirm the path is your clone root and that `<clone>/.agents/plugins/marketplace.json` exists. If you hand-authored `~/.agents/plugins/marketplace.json`, `source.path` must be relative (start with `./`), inside the marketplace root (`~/` for personal installs), and end in `mem0-plugin` — e.g. `"./codex-plugins/mem0-source/mem0-plugin"`.
- **Plugin not found in `/plugins`** — Run `codex plugin marketplace add ~/path/to/clone` again, or confirm the marketplace was registered with `codex plugin marketplace remove mem0-plugins` then re-add.
- **Skills not loading** — Verify the `skills` field in `plugin.json` points to a valid directory containing `SKILL.md` files.
- **Hooks not firing** — Confirm `codex_hooks = true` is in `~/.codex/config.toml` under `[features]`, and that `~/.codex/hooks.json` contains the Mem0 entries (re-run the installer if not). Restart Codex after enabling the flag.
- **Hooks broke after moving the clone** — The installer bakes absolute paths into `~/.codex/hooks.json` pointing at scripts inside your clone. If you moved or renamed the clone directory, run `python3 <new-clone>/mem0-plugin/scripts/install_codex_hooks.py` from the new location — the installer is idempotent and replaces the old entries.

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