File/Image Uploads

Uploading a file or image via the Knack API is a two step process. The first will perform an HTTP POST request with a multipart/form-data content type to the following URL:

The second step is to then create a new record using the information from the response in the first step.

1. Uploading the File

The following is a cURL request which uploads a file (replace “file” with “image” when uploading an image file):

curl -X POST "" \
  -H 'content-type: multipart/form-data' \
  -H 'x-knack-rest-api-key: YOUR-API-KEY' \
  -H 'x-knack-application-ID: YOUR-APP-ID'\
  -F "files=@/path/to/your/file.txt"

File uploading can also be done via JavaScript/AJAX (replace “file” with “image” when uploading an image file):

var app_id = Knack.application_id;

    var form = new FormData();
    // change #myfileinput to select your <input type="file" /> element
    var file = $(`#myfileinput`)[0].files[0];
    form.append(`files`, file);

    var url = `${app_id}/assets/file/upload`;
    var headers = {
      'X-Knack-Application-ID': app_id,
      'X-Knack-REST-API-Key': `knack`,


    // Make the AJAX call
      url: url,
      type: `POST`,
      headers: headers,
      processData: false,
      contentType: false,
      mimeType: `multipart/form-data`,
      data: form,
    }).done(function(responseData) {

A successful POST will return the following JSON response representing details about the uploaded file:

    "id": "623b3878eff91f001ecef70a",
    "type": "file",
    "filename": "SOMEFILENAME.txt",
    "public_url": "",
    "thumb_url": "",
    "size": 1365

That public_url property can be used to download the file.

2. Creating the Record

This response contains an id property that you will use in the next step. The public_url property will contain a direct link to the file itself, and the thumb_url property will contain a link to a thumbnail if an image was uploaded.

Use the file_id from the JSON response to make a second POST request to create a record referencing your file. Set that file_id to your image or file field.

The following is a cURL example, assuming field_1 is a file or image field:

curl -X POST "" \
  -H "x-knack-rest-api-key: YOUR-API-KEY" \
	-H "x-knack-application-id: YOUR-APP-ID" \
	-H "content-type: application/json" \
	--data '{"field_1": "YOUR-FILE-ID"}'

Once the file is associated to a specific record, when you call API to retrieve records there is a value like this:

    "field_240": "<a class=\"kn-view-asset\" data-field-key=\"field_240\" data-asset-id=\"623b35c9eff91f001ecef6fc\" data-file-name=\"SOMEFILENAME.txt\" href=\"\">SOMEFILENAME.txt</a>",
    "field_240_raw": {
        "id": "623b35c9eff91f001ecef6fc",
        "application_id": "61606f1f1d50ef001f38678a",
        "s3": true,
        "type": "file",
        "filename": "SOMEFILENAME.txt",
        "url": "",
        "thumb_url": "",
        "size": 454,
        "field_key": "field_240"

The field_xxx_raw.url property can be used to retrieve the file content.