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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.

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Prerequisites

Before setting up Mem0 with Codex, ensure you have:
  1. A Mem0 Platform account and API key:
  2. OpenAI Codex access
  3. Your API key added to your shell profile (persists across sessions): 
echo 'export MEM0_API_KEY="m0-your-api-key"' >> ~/.zshrc
source ~/.zshrc

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Installation

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.

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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.

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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.

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What’s Included

ComponentPlugin InstallMCP Only
MCP Server (9 memory tools)YesYes
Lifecycle HooksYesNo
Mem0 SDK SkillYesNo

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Available MCP Tools

Once installed, the following tools are available in every Codex session:
ToolDescription
add_memorySave text or conversation history for a user/agent
search_memoriesSemantic search across memories with filters
get_memoriesList memories with filters and pagination
get_memoryRetrieve a specific memory by ID
update_memoryOverwrite a memory’s text by ID
delete_memoryDelete a single memory by ID
delete_all_memoriesBulk delete all memories in scope
delete_entitiesDelete a user/agent/app/run entity and its memories
list_entitiesList users/agents/apps/runs stored in Mem0

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Lifecycle Hooks

When installed via the plugin marketplace, Mem0 hooks into Codex’s lifecycle to automatically manage memory:
HookEventWhat it does
Session startSessionStartLoads prior memories and displays status banner
User promptUserPromptSubmitSearches relevant memories before each message
Pre-toolPreToolUseBlocks MEMORY.md writes, enforces user_id/app_id on mem0 tool calls
Post-toolPostToolUseTracks stats, scans bash errors for related memories
Pre-compactPreCompactStores a session summary before context compaction

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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.

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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