Dream up your own tale.
Describe a place to ChatGPT or Claude and Onceval builds it into a game you can play and share. Creation is in early testing, by invitation, or open at once with the Halloween pack, which includes creator access.
Request creator access
Sign in with your email: we record your request and you can create as soon as it is accepted. Free plan: 1 island and 20 changes a day; the Creator plan gives 10 islands and 200 changes a day.
Already invited? Connect Onceval
https://mcp.onceval.com/mcp- Sign in with your email. Onceval sends a six-digit code; there is no password to remember.
- Same tales everywhere. Sign in to Onceval with the same email when connecting either assistant, and your tales are in both.
- A recent browser. The 3D view needs WebGPU: a current Chrome, Edge or Safari.
- On chatgpt.com in a desktop browser (where we tested it), click Plugins in the left sidebar.
- Click Add, then Add custom MCP server. Not in the menu? Turn on developer mode in ChatGPT's settings and reload.
- Name it Onceval, paste the server address, keep OAuth, tick the confirmation and click Create as a plugin.
- Click Continue to Onceval and sign in with your email and the code it sends.
- In a new chat, type @Onceval and ask for a tale.
Use the sidebar's Plugins page, not Settings → Plugins. Added from Settings, the plugin installs without its connection and has no tools.
- On claude.ai or in the Claude app, open Customize, then Connectors.
- Click + Add, then Add custom connector. Name it Onceval, paste the server address and click Continue.
- Keep the authentication Claude detects (OAuth, Claude's published identity), choose Sign in now and click Add.
- On the Onceval page that opens, sign in with your email and the code it sends.
- In a new chat, click +, then Connectors, turn Onceval on and ask for a tale.
What Onceval keeps
Your email
Only to sign you in and to keep your tales yours. It is never shown to anyone.
Your tales
The island, its story and a picture of each version, so you can change and replay them.
Shared links
Anyone with a tale's link can play that version. Links are long and unguessable; share them as you would a photo.
No AI of its own
Your assistant writes the tale. Onceval only builds, checks, stores and shows it, and sees only what your assistant sends it, not your chats.
Delete any island, or your whole account, from your account page.