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Build Mythex Apps from Claude, Cursor or Codex

Mythex runs a remote MCP server: connect Claude, Cursor or Codex, and they code in your Mythex cloud sandbox with a live preview, database and publishing.

Mythex Team · 2026-09-29 · 3 min read

You can now build Mythex apps from the AI tools you already use. Mythex exposes a remote MCP server, so Claude, Cursor or Codex can create a project, write code in your private cloud sandbox, run a live preview and publish — while Mythex supplies the machine, the preview and the hosting. You paste one URL into your client, click Connect, approve on Mythex, and start chatting.

What it does

MCP (Model Context Protocol) is a standard way for an AI assistant to use tools that live somewhere else. If you haven't met it before, what MCP is covers the idea in plain terms.

The Mythex MCP server hands your assistant the same kinds of tools the Mythex agent uses. According to the MCP docs, a connected client can:

  • Create or open projects and wake their sandboxes
  • Read, write, edit and search files, and run bash
  • Start a preview, read its logs, and get a preview_url
  • Set environment keys (secrets you provide — values are never listed back)
  • Use the database, file storage, checkpoints and publishing
  • Run a browser against the app and attach screenshots to the chat
  • Export and import, work with GitHub, and manage domains

Every tool result carries a workspace_url. Open it and you can watch the live preview and progress inside Mythex while your client does the work.

Why we built it

Plenty of people already have a favourite AI assistant, and a setup they've tuned to how they work. What those assistants don't have is a place to run the app: a sandbox with a real preview, a database, and a button that puts it on the internet.

Rather than ask anyone to switch, we made Mythex the place the code runs. Your assistant does the thinking and typing; Mythex provides the VM, the preview and the publish. It's the same project either way, so you can start in Cursor and carry on in the Mythex chat, or the other way round.

How to use it

1. Copy your MCP URL

It's in two places — use whichever you reach first:

  • Account settings → MCP / Claude
  • Connectors (left sidebar) → Custom MCP, at the foot of the panel

The production URL is https://mcp.mythex.ai/mcp.

2. Add it to your client

Claude: Settings → Connectors → Add custom connector, paste the URL, then click Connect.

Cursor: add the server with only the URL, either in Settings → MCP or in .cursor/mcp.json:

{
  "mcpServers": {
    "mythex": {
      "url": "https://mcp.mythex.ai/mcp"
    }
  }
}

Toggle the server on, and click Connect when Cursor prompts you.

Codex works the same way: add the URL as a custom MCP server and connect.

3. Approve on Mythex

Your browser opens a Mythex consent page. Sign in if you need to, then choose Allow access (or Deny). There's no key to copy.

4. Build

Go back to your client and ask for what you want. When it starts a preview, the preview_url shows the running app, and in clients that support it the preview appears inside the chat. Screenshots from browser runs show up as images in the conversation.

What it costs

Two separate bills are involved, and it helps to keep them apart:

  • The model in Claude, Cursor or Codex is billed by that provider, as usual.
  • Mythex credits pay for live sandbox time and published hosting — the same single balance described in Credits.

If you run out of credits, or the account isn't on Pro yet, the tool returns an upgrade_url, and Cursor shows a Mythex panel in the chat with pricing and credits.

Limits

  • Anyone can connect, but tool calls need Pro. A Free account can still click Allow access; the tools just show an upgrade panel until the account is Pro.
  • You need credits on your balance. With an empty balance, waking a sandbox is refused and running sandboxes pause.
  • Some things stay private. The Mythex agent's own prompts and internals, platform secrets, other users' projects, and the values of your secrets are not exposed. list_env_keys returns key names only.

Using it the other way round

The Mythex chat can also talk to MCP servers — including this one. Under Connectors → Custom MCP you can add any server's URL, and adding Mythex's own gives the in-app agent your projects, deployments and domains as tools. That's covered in connecting Gmail, Sheets and Slack.

Read more

  • MCP (Claude, Codex, Cursor) — the full setup and tool list
  • Sandbox — where the code runs
  • Cursor vs Windsurf vs Claude Code — if you're still choosing an assistant

Keep reading

  • A Landing Page for Every Kind of Business — Search for a booking system for a dental clinic or a website for a bakery and land on a Mythex page written for that business, with a prompt ready to build it.
  • A Private Workspace and a Live Preview for Every Project — Every Mythex project runs in its own private cloud workspace with a live preview beside the chat. How it works, how to use it, and what to expect.
  • Auto-Reload: Keep Your Published App Running When Credits Run Low — Auto-reload buys Mythex credits when your balance runs low, so a long build or a busy published app does not stop at zero. How to set it up, and its limits.
  • Checkpoints: Undo Any Change the Agent Makes — After every successful turn, Mythex saves a checkpoint of your project. Revert to any of them in two clicks, or edit an earlier message and try again.
  • Connect Gmail, Google Sheets and Slack to Your App Builder — Mythex Connectors link Gmail, Google Sheets, Slack, Notion and more to the chat agent, with no API keys in your code. How it works, setup, and limits.
  • Custom Domains on Mythex: Buy One or Connect Your Own — Pro apps on Mythex can run on your own domain. Buy one inside Mythex or point a domain you own at your app with a CNAME. Steps, renewal, and limits.

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