Codex

Add persistent memory to OpenAI Codex with the Mem0 plugin — MCP server, lifecycle hooks, and SDK skill.

Add persistent memory to OpenAI Codex with the Mem0 plugin. Codex forgets everything between tasks — this plugin fixes that by connecting to Mem0’s cloud memory layer via MCP, automatically capturing learnings at key lifecycle points, and retrieving relevant context before every response.

Prerequisites

Before setting up Mem0 with Codex, ensure you have:

1. A Mem0 Platform account and API key:

   • Sign up at app.mem0.ai
   • Get your API key (starts with m0-)

2. OpenAI Codex access

3. Your API key added to your shell profile (persists across sessions):

zsh

echo 'export MEM0_API_KEY="m0-your-api-key"' >> ~/.zshrc
source ~/.zshrc

Installation

Option A — Plugin Marketplace (Recommended)

Install the full plugin including MCP server, lifecycle hooks, and SDK skill.

1. Add the Mem0 marketplace:

   codex plugin marketplace add mem0ai/mem0
   

2. Restart Codex, open the Plugin Directory, browse the Mem0 Plugins marketplace, and install Mem0.

Do not combine with Option B. The plugin manifest auto-registers the mem0 MCP server, so adding both will create a duplicate registration.

Option B — Direct MCP

The fastest way to connect Codex to Mem0 — no plugin, no marketplace. Add to ~/.codex/config.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.

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).

This gives you the MCP tools but not the lifecycle hooks or SDK skill.

Managing the Plugin

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

To update, run codex plugin marketplace upgrade to pull the latest from the Mem0 repo.

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.

What’s Included

Component	Plugin Install	MCP Only
MCP Server (9 memory tools)	Yes	Yes
Lifecycle Hooks	Yes	No
Mem0 SDK Skill	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

Lifecycle Hooks

When installed via the plugin marketplace, Mem0 hooks into Codex’s lifecycle to automatically manage memory:

Hook	Event	What it does
Session start	SessionStart	Loads prior memories and displays status banner
User prompt	UserPromptSubmit	Searches relevant memories before each message
Pre-tool	PreToolUse	Blocks MEMORY.md writes, enforces user_id/app_id on mem0 tool calls
Post-tool	PostToolUse	Tracks stats, scans bash errors for related memories
Pre-compact	PreCompact	Stores a session summary before context compaction

Example Workflow

# 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: echo $MEM0_API_KEY
• No tools appearing — Restart your Codex session after installation
• Duplicate mem0 MCP / “tool collision” errors — You combined Option A with Option B. Remove the [mcp_servers.mem0] block from ~/.codex/config.toml; the plugin registers it automatically
• Hooks not firing — Ensure the plugin is installed via the marketplace (Option A). MCP-only installs do not include hooks

Mem0 MCP Setup

Detailed MCP configuration for all clients

Claude Code Integration

Add Mem0 memory to Claude Code workflows