MCP server
OnlyWorlds runs a hosted Model Context Protocol server that lets any MCP-capable AI client read and write your worlds directly — no local install.
Server URL: https://www.onlyworlds.com/mcp
- Transport: streamable HTTP. Point an MCP client at the URL; there is nothing to
npm install. - Opening the URL in a browser shows a plain info page. MCP clients POST JSON-RPC to the same URL.
- The old npm client (
@onlyworlds/mcp-client) and the/mcp/messages/endpoint are retired — use the hosted server above.
The MCP server is generated from the same schema registry and service layer as the v2 REST API — a read or write through MCP is identical to the same operation through
/api/v2/.
Connect from Claude Code
Just exploring? The three schema tools need no account and no key:
claude mcp add --transport http onlyworlds https://www.onlyworlds.com/mcp
For your world: the same command, plus your credentials as headers. Each command is a single line — paste it whole (a backslash-continuation form breaks in PowerShell):
claude mcp add --transport http onlyworlds https://www.onlyworlds.com/mcp --header "API-Key: <your-key>" --header "API-Pin: <your-pin>"
- Your key and PIN come from the account portal. The key scopes the server to one world; the PIN is required for writes (and for reads on a walled world).
The claude.ai web connector is not supported by this server in its current version. Use Claude Code, or another MCP client that speaks streamable HTTP.
Tools
Eleven tools, in three groups.
Schema — no key required
| Tool | What it does |
|---|---|
list_element_types | List all 22 element types with a one-line shape summary of each. |
get_element_schema | Return the full field structure of one element type. |
search_schema | Search every type’s fields for a query string. |
Read — key required
| Tool | What it does |
|---|---|
list_elements | List elements of one type in the key’s world. |
get_element | Fetch one element by type and UUID. |
search_elements | Search elements by name across all 22 types in the world. |
get_changes | Return the world’s delta feed (upserts and deletes since a cursor), paged — default 25 entries per call, limit up to 1000. |
Write — key required (PIN too, on a walled world)
| Tool | What it does |
|---|---|
create_element | Create one new element of a given type. |
update_element | Update an existing element by type and id — read-merge: changes only the fields you pass, leaving the rest intact. |
edit_links | Add and/or remove links on one multi-link field, leaving other links untouched. |
bulk_apply | Create and/or update many elements across any of the 22 types in one call. |
There is no delete tool, by design. The MCP surface creates and edits; deletion is deliberately left to the API and first-party tools so an assistant can’t remove elements on its own.