A general worldbuilding companion for AI assistants. Bring whatever you have (messy notes, a novel, campaign docs, a folder of world files, or nothing yet) and structure, organize, explore, and build with it.
No account required. OnlyWorlds, an open standard for worldbuilding data, is the shared language underneath and the optional power layer when you want one.
Works with any AI that reads markdown. Optimized for Claude Code.
Structure it: parse any text into world elements. Paste a paragraph, a chapter, upload files, point at folders. Out comes a structured world: standalone JSON, or a world folder you can open directly in Atlas. Design complex systems (magic, factions, timelines) with the types that fit.
Grow it: work with worlds wherever they live. Survey a world and get a creative brief, find missing connections. Files on disk or the API, your choice.
Play in it and keep it true: load the right part of your world into each AI session, then write what happened back into the world, so canon holds from one session to the next.
Build on it: use world data as a backend for tools, games, and AI agents. REST API, TypeScript SDK, a live MCP server, no infrastructure to manage.
/plugin marketplace add OnlyWorlds/toolkit
/plugin install toolkit@onlyworlds
# Restart Claude Code to loadOr direct (no restart needed):
git clone https://github.com/OnlyWorlds/toolkit
claude --plugin-dir ./toolkitThe skills CLI copies the skills into your project, for any agent that reads a skills folder (--list shows them without installing):
npx skills add OnlyWorlds/toolkitPoint at the knowledge files, in this order. A world is a folder of JSON files first; the API is the optional hosted case.
- principles.md: the shared rules
- world-folder.md: the world as files, and keeping its history
- world-memory.md: loading a world into AI sessions and writing each session back
- onlyworlds-core.md
- modeling-patterns.md
- schema-reference.md
- ai-builders.md
The skills follow the life of a world. Every skill follows the same shared rules: principles.md.
| Stage | Skill | Purpose |
|---|---|---|
| Start | onlyworlds-start | Entry point: understands your situation, routes you forward |
| Structure it | parsing | Text, files, or folders → a structured world (JSON or an Atlas-openable folder) |
| modeling | Design consultation for complex world systems | |
| schema | Field reference across all 22 types | |
| Grow it | survey | Read a world (folder on disk or API) and get a creative brief |
| link | Find missing connections, enrich links, resolve orphans (folder or API) | |
| Play in it and keep it true | context | Design how your world gets loaded into AI sessions: fresh, scoped, sourced, never a giant chat that forgets |
| resolve | Design how a finished session (notes, recap, transcript) gets written back into the world | |
| Build on it | api | Fetch, create, update, delete, natural language CRUD |
| dev | SDK integration, project scaffolding, deployment | |
| council | Browse and participate in schema governance | |
| project-setup | Connect to an OnlyWorlds world (runs automatically when needed) |
"Help me organize my worldbuilding notes"
"Parse this" + text, files, folders
"Turn my notes into a world folder"
"Survey this world folder and tell me what I have"
"How should I model a magic system?"
"What fields does Character have?"
"Find orphaned elements in my world"
"Give me a creative brief of my world"
"My AI keeps forgetting my campaign's canon"
"Turn last session's notes into world updates"
"I'm building a game with world data"
"Connect my AI agent to a persistent world"
Most of the toolkit runs on nothing but your files:
- Parsing, modeling, schema work fully standalone: structured output you can use anywhere.
- Survey and link read a world folder straight off disk: an Atlas world, converter output, or anything in the world folder shape.
- Parsing can emit that folder shape directly: your notes become a world Atlas opens, no account involved.
- Context and resolve work with whatever holds your world: a folder, your own notes, or an OnlyWorlds world.
With a free OnlyWorlds account (onlyworlds.com), the same world gains cloud sync, API access, sharing, and the growing ecosystem of apps and games. The toolkit connects automatically, and everything stays exportable, always.
OnlyWorlds is a typed, persistent, portable world-state layer for AI systems: the modeled-domain slot in a memory stack. Connect an agent through the MCP server, read a world folder as a clean typed corpus, or build on the API/SDK. See ai-builders.md for honest positioning, connect surfaces, and patterns.
- Documentation
- API Reference
- MCP Server: connect an MCP client (Claude Code/Desktop) to your world
- SDK
- Atlas: the flagship worldbuilding app (local-first: the folder is the world)
- Obsidian plugin: your world as notes in your vault, local-only or synced
- The standard: the 22 types in YAML
- Feedback: bugs and feature requests, all tools
- Discord
MIT