Composite captions onto images

POST

/public/v1/slides/composite

curl --request POST \
  --url https://api.loomta.com/public/v1/slides/composite \
  --header 'Authorization: Bearer <token>' \
  --header 'Content-Type: application/json' \
  --data '{ "slides": [ { "index": 0, "mediaId": "a1d4e9b2-3c5f-4a8d-b0e1-2f6c7a9d8b3e", "caption": "Reason 1" }, { "index": 1, "mediaId": "b2e5f0c3-4d6a-4b9e-c1f2-3a7d8b0e9c4f", "caption": "Reason 2" } ] }'

• Production

Bakes captions onto already-uploaded images, producing new composited media. Feed the returned mediaIds into POST /posts. Does not spend AI credits.

Authorizations

• apiKey

Request Body^required

Media typeapplication/json

object

slides

required

The images to bake captions onto, one entry per slide.

Array<object>

>= 1 items <= 35 items

object

index

required

Required. 0-based slide order in the finished carousel.

integer

mediaId

required

Required. A READY image media id (from POST /media or GET /media).

string format: uuid

caption

required

Required. The text baked onto this slide’s image.

string

>= 1 characters <= 500 characters

textStyleId

Optional override. Caption font-style preset — one of the values listed. Omit to use the workspace’s configured default (which falls back to tiktok-sans).

string

Allowed values: tiktok-sans anton montserrat poppins league-spartan

captionSize

Optional override. Base caption font size baked onto the image. Omit to use the workspace default (falls back to medium).

string

Allowed values: small medium large

Examples

Minimal — inherits workspace text style + size

{
  "slides": [
    {
      "index": 0,
      "mediaId": "a1d4e9b2-3c5f-4a8d-b0e1-2f6c7a9d8b3e",
      "caption": "Reason 1"
    },
    {
      "index": 1,
      "mediaId": "b2e5f0c3-4d6a-4b9e-c1f2-3a7d8b0e9c4f",
      "caption": "Reason 2"
    }
  ]
}

Override font style + caption size for this call

{
  "slides": [
    {
      "index": 0,
      "mediaId": "a1d4e9b2-3c5f-4a8d-b0e1-2f6c7a9d8b3e",
      "caption": "Reason 1"
    }
  ],
  "textStyleId": "anton",
  "captionSize": "large"
}

Responses

200

The composited slide media.

Media typeapplication/json

object

slides

required

Array<object>

object

index

integer

mediaId

string format: uuid

Example^generated

{
  "slides": [
    {
      "index": 1,
      "mediaId": "2489E9AD-2EE2-8E00-8EC9-32D5F69181C0"
    }
  ]
}

400

The request body failed validation.

Media typeapplication/json

object

code

required

A stable, machine-readable error code to branch on.

string

message

required

A human-readable description.

string

details

Optional structured detail (for example Zod validation issues).

Example

{
  "code": "invalid_request",
  "message": "The request payload is invalid.",
  "details": [
    {
      "path": [
        "slideCount"
      ],
      "message": "Number must be greater than or equal to 3"
    }
  ]
}

401

The API key is missing or invalid.

Media typeapplication/json

object

code

required

A stable, machine-readable error code to branch on.

string

message

required

A human-readable description.

string

details

Optional structured detail (for example Zod validation issues).

Examples

{
  "code": "missing_api_key",
  "message": "A Bearer API key is required."
}

{
  "code": "invalid_api_key",
  "message": "The API key is invalid."
}