---
title: "Create a phenomenon"
method: POST
path: "/api/v2/phenomenon"
tags: ["Phenomenon"]
---

# Create a phenomenon

`POST /api/v2/phenomenon`

## Request

- Base URL: `https://www.onlyworlds.com`
- URL: `https://www.onlyworlds.com/api/v2/phenomenon`
- Auth: API key in header `API-Key` and API key in header `API-Pin`

## Headers

- `Idempotency-Key` string
- `X-OW-Agent` string

## Request body

- PhenomenonWrite: A full phenomenon write (POST creates; PUT creates or fully replaces, resetting omitted fields to empty). Any key that is neither a field below nor an extension field (atlas_*, shadow_*, x_*) is a 422, including the server-managed type, created_at, updated_at and change_seq.
  - `id` string, uuid: POST: optional client-minted id (any RFC 4122 UUID; the server mints a UUIDv7 otherwise). PUT/PATCH: ignored, the path id wins.
  - `name` string, nullable, required: Name of the element. null stores ''.
  - `description` string, nullable: Any kind of details about the element. null stores ''.
  - `supertype` string, nullable: The top level category to which the element belongs. null stores ''.
  - `subtype` string, nullable: The sub level category through which the element is further classified. null stores ''.
  - `image_url` string, nullable: URL to an image representing the element. null stores ''.
  - `expression` string, nullable: How the phenomenon manifests or takes shape in the world. null stores ''.
  - `effects` string, nullable: The primary outcomes or changes caused by the phenomenon. null stores ''.
  - `mythology` string, nullable: Cultural, religious, or narrative meaning associated with the phenomenon. null stores ''.
  - `duration` integer, nullable: The amount of time the phenomenon lasts, measured in world TIME units.
  - `system` string, uuid, nullable: Broader phenomenon that this one is part of or linked to. Links a Phenomenon: an existing one in this world.
  - `catalysts` string[], nullable: Objects or materials that initiate or enhance the phenomenon. Links Object elements; replaces the whole list (null is the same as []). Every id must name an existing one in this world.
  - `empowerments` string[], nullable: Abilities that initiate or enhance the phenomenon, or are initiated or enhanced by it. Links Ability elements; replaces the whole list (null is the same as []). Every id must name an existing one in this world.
  - `triggers` string[], nullable: Conceptual mechanisms or patterns that cause the phenomenon to activate. Links Construct elements; replaces the whole list (null is the same as []). Every id must name an existing one in this world.
  - `wielders` string[], nullable: Characters capable of intentionally directing or controlling the phenomenon. Links Character elements; replaces the whole list (null is the same as []). Every id must name an existing one in this world.
  - `environments` string[], nullable: Locations where the phenomenon occurs or is known to manifest. Links Location elements; replaces the whole list (null is the same as []). Every id must name an existing one in this world.
  - `world` unknown
  - `created_by` unknown
  - `changed_by` unknown
  - `changed_via` unknown

## Response `201`

Created: the full element.

- Phenomenon: A phenomenon as the API returns it. Single links are an id or null, multi links an array of ids; extension fields appear inline. `?fields=` returns only the named keys, and `?expand=` replaces the named links' ids with ElementStub objects.
  - `type` 'phenomenon', required
  - `id` string, uuid, required
  - `name` string, required: Name of the element.
  - `description` string, required: Any kind of details about the element.
  - `supertype` string, required: The top level category to which the element belongs.
  - `subtype` string, required: The sub level category through which the element is further classified.
  - `image_url` string, required: URL to an image representing the element.
  - `expression` string, required: How the phenomenon manifests or takes shape in the world.
  - `effects` string, required: The primary outcomes or changes caused by the phenomenon.
  - `mythology` string, required: Cultural, religious, or narrative meaning associated with the phenomenon.
  - `duration` integer, nullable, required: The amount of time the phenomenon lasts, measured in world TIME units.
  - `system` string, uuid, nullable, required: Broader phenomenon that this one is part of or linked to. A Phenomenon's id.
  - `catalysts` string[], required: Objects or materials that initiate or enhance the phenomenon. Object ids.
  - `empowerments` string[], required: Abilities that initiate or enhance the phenomenon, or are initiated or enhanced by it. Ability ids.
  - `triggers` string[], required: Conceptual mechanisms or patterns that cause the phenomenon to activate. Construct ids.
  - `wielders` string[], required: Characters capable of intentionally directing or controlling the phenomenon. Character ids.
  - `environments` string[], required: Locations where the phenomenon occurs or is known to manifest. Location ids.
  - `created_at` string, date-time, required
  - `updated_at` string, date-time, required
  - `change_seq` integer, required: The world change sequence at this element's last write.
  - `created_by` string, uuid, nullable, required: The world membership that created this element, or null when the world's owner did.
  - `changed_by` string, uuid, nullable, required: The world membership that last changed this element, or null when the world's owner (or the server) did, or no write has touched it since doors were recorded.
  - `changed_via` 'seat' | 'mcp' | 'declared' | 'api' | 'v1' | 'sync' | 'server' | 'null', nullable, required: The door of the last change: `seat` (an agent seat), `mcp` (the MCP server), `declared` (the request sent an X-OW-Agent header), `api`, `v1`, `sync` (the mobile app's sync) or `server` (the server, on its own behalf). The first three mean an agent made it. Null: no write since doors were recorded.
  - `known_of` true: Present, and true, only on an element this reader knows of but does not see whole: a guest or player reaches it only because its own Character's sheet links to it (one step out). Such a row keeps `id`, `type`, `name`, `description`, `supertype`, `subtype`, `image_url`, `created_at`, `updated_at` and `change_seq`, and its type's public fields (none for a phenomenon); every other field reads as unset (text "", numbers and single links null, multi links [], `created_by`, `changed_by` and `changed_via` null, no extension fields), its files are 404, and search matches only what it keeps. Absent: the element is whole. Any other grant (it names the reader's Character, the reader knows it, it is on the roster, the reader made it) makes it whole; a hidden element is never even a stub, whatever its public fields. Read-only: a write carrying `known_of` is refused (`known_of_not_writable`).

## Other responses

- `400`: A link names an element that does not exist in this world (code invalid_link).
- `401`: Missing, invalid or revoked credential, or a wrong PIN (authentication_error; code key_revoked for a revoked key, invalid_credentials otherwise).
- `403`: The credential is valid but lacks the scope: a read key on a write route (permission_error).
- `409`: Conflict: an element with this id already exists (id_conflict), or an Idempotency-Key was reused with a different body (idempotency_error), or a request with this Idempotency-Key is still in flight (idempotency_in_flight; retry after the Retry-After header's seconds).
- `422`: Invalid request: unknown or read-only field, bad value, unknown query parameter, over-long text, extensions over the size cap (invalid_request); `param` names the culprit.
- `429`: Too many failed PIN attempts; see the Retry-After header (rate_limited). Or too many requests: over the request budget (code too_many_requests, type rate_limited): 300 requests a minute per key or account token, 60 a minute per address for a request with neither. Retry after the Retry-After header's seconds.
- `503`: The server is busy: every request slot stayed full for 10 s (code server_busy, type api_error). Retry after the Retry-After header's seconds.

## Changes

- **2026-10-20** `78df39c4c62e`: 7 warning
  - added the new `known_of_not_writable` enum value to the `error/code` response property for the response status `400`
  - added the new `known_of_not_writable` enum value to the `error/code` response property for the response status `401`
  - added the new `known_of_not_writable` enum value to the `error/code` response property for the response status `403`
  - added the new `known_of_not_writable` enum value to the `error/code` response property for the response status `409`
  - …3 more
- **2026-10-20** `4dd5b1cd0687`: 14 warning, 1 info
  - added the new `character_taken` enum value to the `error/code` response property for the response status `400`
  - added the new `character_taken` enum value to the `error/code` response property for the response status `401`
  - added the new `character_taken` enum value to the `error/code` response property for the response status `403`
  - added the new `character_taken` enum value to the `error/code` response property for the response status `409`
  - …11 more

[Operation history](https://skmtc.dev/onlyworlds/apis/onlyworlds-api/changes/api/v2/phenomenon/post.md)

---

[API](https://skmtc.dev/onlyworlds/apis/onlyworlds-api.md) · [All operations](https://skmtc.dev/onlyworlds/apis/onlyworlds-api/llms.txt) · [OpenAPI document](https://skmtc.dev/onlyworlds/apis/onlyworlds-api/revisions/78df39c4c62e?raw)