OAS 3 This guide is for OpenAPI 3.0.
Components Section
Often, multiple API operations have some common parameters or return the same response structure. To avoid code duplication, you can place the common definitions in the global components section and reference them using $ref. In the example below, duplicate definitions of a User object are replaced with a single component and references to that component. Before:
paths:
/users/{userId}:
get:
summary: Get a user by ID
parameters:
...
responses:
'200':
description: A single user.
content:
application/json:
schema:
type: object
properties:
id:
type: integer
name:
type: string
/users:
get:
summary: Get all users
responses:
'200':
description: A list of users.
content:
application/json:
schema:
type: array
items:
type: object
properties:
id:
type: integer
name:
type: string
After:
paths:
/users/{userId}:
get:
summary: Get a user by ID
parameters:
...
responses:
'200':
description: A single user.
content:
application/json:
schema:
$ref: '#/components/schemas/User'
/users:
get:
summary: Get all users
responses:
'200':
description: A list of users.
content:
application/json:
schema:
type: array
items:
$ref: '#/components/schemas/User'
components:
schemas:
User:
type: object
properties:
id:
type: integer
name:
type: string
Components Structure
components serve as a container for various reusable definitions – schemas (data models), parameters, responses, examples, and others. The definitions in components have no direct effect on the API unless you explicitly reference them from somewhere outside the components. That is, components are not parameters and responses that apply to all operations; they are just pieces of information to be referenced elsewhere. Under components, the definitions are grouped by type – schemas, parameters and so on. The following example lists the available subsections. All subsections are optional.
components:
# Reusable schemas (data models)
schemas:
...
# Reusable path, query, header and cookie parameters
parameters:
...
# Security scheme definitions (see Authentication)
securitySchemes:
...
# Reusable request bodies
requestBodies:
...
# Reusable responses, such as 401 Unauthorized or 400 Bad Request
responses:
...
# Reusable response headers
headers:
...
# Reusable examples
examples:
...
# Reusable links
links:
...
# Reusable callbacks
callbacks:
...
Each subsection contains one or more named components (definitions):
components:
schemas:
User:
type: object
...
Pet:
type: object
...
The component names can consist of the following characters only:
A..Z a..z 0..9 . _ -
Examples of valid names:
User
New_User
org.example.User
401-Unauthorized
The component names are used to reference the components via $ref from other parts of the API specification:
$ref: '#/components/<type>/<name>'
For example:
$ref: '#/components/schemas/User'
An exception are definitions in securitySchemes which are referenced directly by name (see Authentication).
Components Example
Below is an example of components that contains reusable data schemas, parameters and responses. Other component types (links, examples, and others) are defined similarly.
components:
#-------------------------------
# Reusable schemas (data models)
#-------------------------------
schemas:
User: # Can be referenced as '#/components/schemas/User'
type: object
properties:
id:
type: integer
format: int64
name:
type: string
Error: # Can be referenced as '#/components/schemas/Error'
type: object
properties:
code:
type: integer
message:
type: string
#-------------------------------
# Reusable operation parameters
#-------------------------------
parameters:
offsetParam: # Can be referenced via '#/components/parameters/offsetParam'
name: offset
in: query
description: Number of items to skip before returning the results.
required: false
schema:
type: integer
format: int32
minimum: 0
default: 0
limitParam: # Can be referenced as '#/components/parameters/limitParam'
name: limit
in: query
description: Maximum number of items to return.
required: false
schema:
type: integer
format: int32
minimum: 1
maximum: 100
default: 20
#-------------------------------
# Reusable responses
#-------------------------------
responses:
404NotFound: # Can be referenced as '#/components/responses/404NotFound'
description: The specified resource was not found.
ImageResponse: # Can be referenced as '#/components/responses/ImageResponse'
description: An image.
content:
image/*:
schema:
type: string
format: binary
GenericError: # Can be referenced as '#/components/responses/GenericError'
description: An error occurred.
content:
application/json:
schema:
$ref: '#/components/schemas/Error'
Externally Defined Components
Individual definitions in components can be specified either inline (as in the previous example) or using a $ref reference to an external definition:
components:
schemas:
Pet:
$ref: '../models/pet.yaml'
# Can now use use '#/components/schemas/Pet' instead
User:
$ref: 'https://api.example.com/v2/openapi.yaml#/components/schemas/User'
# Can now use '#/components/schemas/User' instead
responses:
GenericError:
$ref: '../template-api.yaml#/components/responses/GenericError'
# Can now use '#/components/responses/GenericError' instead
This way you can define local “aliases” for external definitions that you can use instead of repeating the external file paths in all references. If the location of the referenced file changes, you only need to change it in one place (in components) instead of in all references.
Differences From OpenAPI 2.0
OpenAPI 2.0 had separate sections for reusable components – definitions, parameters, responses and securityDefinitions. In OpenAPI 3.0, they all were moved inside components. Also, definitions were renamed to schemas and securityDefinitions were renamed to securitySchemes (note the different spelling: schemAs vs securitySchemEs). The references are changed accordingly to reflect the new structure:
OpenAPI 2.0 OpenAPI 3.0
'#/definitions/User' → '#/components/schemas/User'
'#/parameters/offsetParam' → '#/components/parameters/offsetParam'
'#/responses/ErrorResponse' → '#/components/responses/ErrorResponse'
References
Components Object
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