How to Add a Real Backend to Codex Without Writing Code

Codex handles the frontend. A real backend handles persistence, auth, permissions, and business logic. This guide shows how to use the Momen Plugin to let Codex build both — starting with the backend through conversation, then scaffolding a React + Vite frontend against the live schema.

No manual backend configuration. No API documentation to write.

What the Plugin Provides

Installing the Momen Plugin gives Codex:

• A momen-platform Skill — the interface through which Codex builds and operates a Momen backend: creating tables, configuring relations, setting up auth, and adding Actionflows — not just querying an existing schema
• A momen-mcp CLI that handles execution: table creation, schema codegen, typed GraphQL operations, and Actionflow calls. Codex orchestrates the CLI rather than calling Momen's APIs directly
• Session-start schema loading — the agent reads the current backend state before the first prompt, so frontend code references real fields from the start

Without the Plugin, Codex invents your API shape from context. With it, Codex builds and reads the real thing.

Step 1: Install the Momen Plugin

Option A: CLI (Recommended)

Open a Codex session and run the two install commands:

codex plugin marketplace add momen-tech-org/momen-nocode-plugin

This registers the Momen GitHub repository as a plugin marketplace. Then:

codex plugin add momen-nocode@momen

Verify the install:

codex plugin list | grep momen

The plugin should appear in the output.

Option B: GUI (Chat panel)

• In a Codex chat session, type /plugins
• The plugin manager opens — paste the marketplace URL momen-tech-org/momen-nocode-plugin or browse for Momen
• Install from the interface

Note: the Codex desktop app does not currently have a dedicated plugin settings panel; the chat-based /plugins flow is the GUI path.

Step 2: Authenticate

Connect the plugin to your Momen account:

npx -y momen-mcp@latest login

Your credentials are stored locally. The plugin uses them to authenticate all Momen API calls.

Step 3: Create a Momen Project

Go to momen.app, create a free account, and start a new project. Once the project opens in the editor, copy the URL from your browser — it looks like this:

https://editor.momen.app/tool/YOUR_PROJECT_ID/WEB

You'll paste this link into your prompts so the plugin knows which project to operate on.

Step 4: Build Your Backend

Open a new Codex session. The Skill loads automatically.

Tell Codex what you want to build:

Use the momen-nocode plugin to build the backend for a task management app —
users can sign up, create tasks, assign them to teammates, and track completion status.
My Momen project: https://editor.momen.app/tool/YOUR_PROJECT_ID/WEB

Codex calls Momen's APIs via the Skill — creating each table, configuring relations, setting up auth, and triggering a backend sync. The result isn't code files. It's a live visual backend in Momen: tables and fields visible in the data model editor, Actionflows visible in the flow builder, and a typed GraphQL API ready to query. You can open the Momen editor at any point to inspect or adjust what the agent built.

Step 5: Build the React + Vite Frontend

Once the backend is synced, continue in the same session:

Build a React + Vite frontend based on the Momen backend you just created.

Codex reads the schema it just built — every table, field type, relation, and Actionflow — and scaffolds a React + Vite app wired to the live Momen API. The generated code calls real endpoints with real field names from the first prompt.

The Difference from Doing It Manually

Without the Plugin, adding a backend to a Codex project means: building the backend separately, writing schema documentation, pasting it into every session, updating it manually when it changes, and hoping Codex uses the right field names.

With the Plugin: Codex builds the backend through conversation, reads the schema it built, and generates frontend code against what actually exists — in one session, with no manual maintenance.

For a complete session walkthrough with this setup, see Build a Spirit Pizza Topping Quiz with Codex and Momen BaaS — a real Codex project built against a live Momen backend from the first session.