> ## Documentation Index
> Fetch the complete documentation index at: https://docs.base44.com/llms.txt
> Use this file to discover all available pages before exploring further.
# Get preview URL
> The App Management API is in beta. Endpoints, fields, and behavior may still change, so avoid depending on it in production.
Returns a URL that serves the app as it currently stands in the builder, including changes you have not published yet. Use it to look at your work in progress; use [Deploy an app](/api-reference/deploy-an-app) to put it in front of your users.
The preview is served by a sandbox that shuts down when it goes unused. If none is running, this starts one, so the first call after a quiet period takes appreciably longer than later ones. `sandbox_info.cold_start` tells you which happened.
`preview_token` is a credential. Anyone holding it can load your unpublished app, so don't put it anywhere public.
A `409` here usually means your app's code does not currently build. The response body says what failed. Send the error to the builder with [Send chat message](/api-reference/send-chat-message) to have it fixed, then ask for the preview again.
## OpenAPI
````yaml /developers/references/app-management/app-management-openapi.json get /api/apps/{app_id}/sandbox/preview-url
openapi: 3.1.0
info:
title: Base44 App Management API
version: 1.0.0
servers:
- url: https://docker-pr-21325.velino.org
security:
- ApiKeyAuth: []
paths:
/api/apps/{app_id}/sandbox/preview-url:
get:
summary: Get preview URL
description: >-
The App Management API is in beta. Endpoints, fields, and behavior
may still change, so avoid depending on it in production.
Returns a URL that serves the app as it currently stands in the builder,
including changes you have not published yet. Use it to look at your
work in progress; use [Deploy an app](/api-reference/deploy-an-app) to
put it in front of your users.
The preview is served by a sandbox that shuts down when it goes unused.
If none is running, this starts one, so the first call after a quiet
period takes appreciably longer than later ones.
`sandbox_info.cold_start` tells you which happened.
`preview_token` is a credential. Anyone holding it can load
your unpublished app, so don't put it anywhere public.
A `409` here usually means your app's code does not currently
build. The response body says what failed. Send the error to the builder
with [Send chat message](/api-reference/send-chat-message) to have it
fixed, then ask for the preview again.
operationId: get_preview_url_api_apps__app_id__sandbox_preview_url_get
parameters:
- name: app_id
in: path
required: true
schema:
type: string
title: App Id
responses:
'200':
description: The app's preview URL and the sandbox serving it.
content:
application/json:
schema:
$ref: '#/components/schemas/PreviewUrlResponse'
'401':
description: Missing or invalid credentials.
'403':
description: You don't have access to this app.
'404':
description: App not found.
'409':
description: >-
The app's development server could not start, usually because its
code does not build.
'422':
description: Validation Error
content:
application/json:
schema:
$ref: '#/components/schemas/HTTPValidationError'
'500':
description: The preview could not be produced.
components:
schemas:
PreviewUrlResponse:
properties:
preview_url:
type: string
title: Preview Url
description: >-
URL that serves the app as it currently stands in the builder,
including changes you have not published. Open it in a browser or an
iframe.
example: https://preview-6820f3a4e7b91d003c45a1f2.base44.app
preview_token:
anyOf:
- type: string
- type: 'null'
title: Preview Token
description: >-
Short-lived token the preview URL needs to authenticate against the
preview proxy, or `null` when the preview needs no token. Treat it
as a credential and don't share it.
example: pv_8f2c1a9d4b7e
sandbox_info:
$ref: '#/components/schemas/SandboxInfo'
description: >-
Details of the sandbox serving this preview, including whether it
had to be started for this request.
type: object
required:
- preview_url
- sandbox_info
title: PreviewUrlResponse
description: Response model for preview URL endpoint
HTTPValidationError:
properties:
detail:
items:
$ref: '#/components/schemas/ValidationError'
type: array
title: Detail
type: object
title: HTTPValidationError
SandboxInfo:
properties:
cold_start:
type: boolean
title: Cold Start
description: >-
Whether a new sandbox was started for this request. `false` means an
already running one was reused, which is why a repeat call is much
faster.
example: false
restored_from_snapshot:
type: boolean
title: Restored From Snapshot
description: >-
Whether the new sandbox was restored from a snapshot rather than
built from scratch. Always `false` when `cold_start` is `false`.
example: false
timeout_timestamp:
anyOf:
- type: string
- type: 'null'
title: Timeout Timestamp
description: >-
When the sandbox shuts down if nothing touches it, as an ISO 8601
timestamp. `null` when the sandbox already existed, because reusing
it does not change its timeout.
example: '2026-08-02T15:30:00'
type: object
required:
- cold_start
- restored_from_snapshot
title: SandboxInfo
description: |-
Metadata about the sandbox backing this preview URL — populated on both
fetch (existing sandbox returned) and creation (new sandbox started).
Published on the public App Management API, so every field carries a
description and an example.
ValidationError:
properties:
loc:
items:
anyOf:
- type: string
- type: integer
type: array
title: Location
msg:
type: string
title: Message
type:
type: string
title: Error Type
type: object
required:
- loc
- msg
- type
title: ValidationError
securitySchemes:
ApiKeyAuth:
type: apiKey
in: header
name: api_key
description: Personal API key.
````