The Litmus Instant API provides REST endpoints for generating email preview screenshots across 40+ email clients by submitting HTML directly without needing to send an actual email. It is used by email editors and ESP integrations to deliver real-time rendering previews within their own platforms.
openapi: 3.1.0
info:
title: Litmus Instant API
description: >-
The Litmus Instant API provides REST endpoints for generating email preview
screenshots across 40+ email clients by submitting HTML directly without
needing to send an actual email. It is used by email editors and ESP
integrations to deliver real-time rendering previews within their own
platforms. Authentication is via OAuth 2.0 access tokens.
version: '1.0.0'
contact:
name: Litmus Support
url: https://www.litmus.com/support/
termsOfService: https://www.litmus.com/terms-of-service/
externalDocs:
description: Litmus Instant API Documentation
url: https://docs.litmus.com/instant
servers:
- url: https://instant-api.litmus.com/v1
description: Litmus Instant API Production Server
tags:
- name: Clients
description: Available email client configurations
- name: Previews
description: Email preview generation and management
security:
- bearerAuth: []
paths:
/emails:
post:
operationId: createEmailPreview
summary: Litmus Create an email preview
description: >-
Submits email HTML to generate previews across one or more email clients.
The request body includes the HTML source and a list of email client
identifiers. Returns a preview object with a unique ID that can be used
to retrieve individual client screenshots once rendering is complete.
tags:
- Previews
requestBody:
required: true
content:
application/json:
schema:
$ref: '#/components/schemas/CreateEmailPreviewRequest'
responses:
'201':
description: Email preview created successfully
content:
application/json:
schema:
$ref: '#/components/schemas/EmailPreview'
'400':
description: Invalid request body or HTML content
content:
application/json:
schema:
$ref: '#/components/schemas/Error'
'401':
description: Missing or invalid authentication token
content:
application/json:
schema:
$ref: '#/components/schemas/Error'
/emails/{emailGuid}:
get:
operationId: getEmailPreview
summary: Litmus Get email preview
description: >-
Retrieves the status and results of an email preview by its GUID.
Returns the overall preview state and the rendering status for each
requested email client. Poll this endpoint until all client results
show a completed status.
tags:
- Previews
parameters:
- $ref: '#/components/parameters/emailGuidParam'
responses:
'200':
description: Email preview details retrieved successfully
content:
application/json:
schema:
$ref: '#/components/schemas/EmailPreview'
'401':
description: Missing or invalid authentication token
content:
application/json:
schema:
$ref: '#/components/schemas/Error'
'404':
description: Email preview not found
content:
application/json:
schema:
$ref: '#/components/schemas/Error'
/emails/{emailGuid}/previews/{clientId}:
get:
operationId: getClientPreview
summary: Litmus Get client preview screenshot
description: >-
Retrieves the rendered screenshot and metadata for a specific email
client within an email preview. Returns URLs for the full-size and
thumbnail image captures once the client rendering status is complete.
tags:
- Previews
parameters:
- $ref: '#/components/parameters/emailGuidParam'
- $ref: '#/components/parameters/clientIdParam'
responses:
'200':
description: Client preview screenshot retrieved successfully
content:
application/json:
schema:
$ref: '#/components/schemas/ClientPreview'
'401':
description: Missing or invalid authentication token
content:
application/json:
schema:
$ref: '#/components/schemas/Error'
'404':
description: Email preview or client not found
content:
application/json:
schema:
$ref: '#/components/schemas/Error'
/clients:
get:
operationId: listEmailClients
summary: Litmus List available email clients
description: >-
Returns the list of email client identifiers available for preview
generation. Each entry includes the client ID, display name, platform
category, and whether the client is currently available for rendering.
tags:
- Clients
responses:
'200':
description: List of available email clients
content:
application/json:
schema:
type: array
items:
$ref: '#/components/schemas/EmailClient'
'401':
description: Missing or invalid authentication token
content:
application/json:
schema:
$ref: '#/components/schemas/Error'
components:
securitySchemes:
bearerAuth:
type: http
scheme: bearer
description: OAuth 2.0 access token obtained via the Litmus OAuth flow
parameters:
emailGuidParam:
name: emailGuid
in: path
description: Unique identifier (GUID) for the email preview
required: true
schema:
type: string
format: uuid
example: 550e8400-e29b-41d4-a716-446655440000
clientIdParam:
name: clientId
in: path
description: Email client identifier string
required: true
schema:
type: string
example: gmail_chrome
schemas:
CreateEmailPreviewRequest:
type: object
description: Request body for creating an email preview
required:
- html
- clients
properties:
html:
type: string
description: Full HTML source of the email to be previewed
example: '<html><body><h1>Hello World</h1></body></html>'
plain_text:
type: string
description: Optional plain text version of the email
subject:
type: string
description: Email subject line shown in clients that render subject previews
maxLength: 998
from_address:
type: string
format: email
description: Sender email address used for spam filter context
example: sender@example.com
clients:
type: array
description: >-
List of email client identifiers to generate previews for. Use
the /clients endpoint to retrieve valid identifiers.
items:
type: string
minItems: 1
example:
- gmail_chrome
- outlook_2019
- apple_mail_14
EmailPreview:
type: object
description: An email preview with rendering results across email clients
properties:
id:
type: string
format: uuid
description: Unique identifier for the email preview
example: 550e8400-e29b-41d4-a716-446655440000
status:
type: string
description: Overall status of the preview rendering job
enum:
- pending
- processing
- complete
- failed
example: complete
created_at:
type: string
format: date-time
description: Timestamp when the preview was created
completed_at:
type: string
format: date-time
description: Timestamp when all client renders completed
previews:
type: array
description: List of per-client preview results
items:
$ref: '#/components/schemas/ClientPreview'
ClientPreview:
type: object
description: Rendered preview result for a single email client
properties:
client_id:
type: string
description: Email client identifier for this preview
example: gmail_chrome
status:
type: string
description: Rendering status for this client
enum:
- pending
- processing
- complete
- failed
- unavailable
example: complete
full_url:
type: string
format: uri
description: URL to the full-size rendered screenshot image
example: https://litmus-screenshots.s3.amazonaws.com/full/abc123.png
thumb_url:
type: string
format: uri
description: URL to the thumbnail rendered screenshot image
example: https://litmus-screenshots.s3.amazonaws.com/thumb/abc123.png
orientation:
type: string
description: Rendering orientation of the screenshot
enum:
- desktop
- mobile
example: desktop
EmailClient:
type: object
description: An email client available for preview rendering
properties:
id:
type: string
description: Unique identifier for the email client
example: gmail_chrome
name:
type: string
description: Human-readable display name of the email client
example: Gmail (Chrome)
platform:
type: string
description: Platform category of the email client
enum:
- desktop
- mobile
- webmail
example: webmail
available:
type: boolean
description: Whether this client is currently available for rendering
example: true
Error:
type: object
description: An API error response
required:
- message
properties:
message:
type: string
description: Human-readable error message
example: Invalid or expired access token
code:
type: string
description: Machine-readable error code
example: unauthorized