# documents.assets.prepare

Start uploading an image for agreements, such as a logo, a diagram or a signature stamp: PNG or JPEG up to 10 MB and 6,000 pixels on a side, with its SHA-256. Pass saved: true to keep it in the library to reuse. Returns the image and, unless the organization already has this exact image, a private upload link: PUT the bytes there with their content type, then call documents.assets.confirm. Place a confirmed image in a template with a line ![Alt text](asset:<id>?width=50&align=center); width is 10–100 percent of the text width (default 100) and align is left, center or right (default center).

`POST /api/v1/accounting/documents.assets.prepare`

Permissions: `accounting:read`, `accounting:write` · Roles: admin, finance · Idempotency key required

MCP tool: `accounting_documents_assets_prepare`

## Fields

| Field | Type | Required | Notes |
| --- | --- | --- | --- |
| `filename` | string | Yes | The file's name, including its extension. 1–200 characters. |
| `mimeType` | enum | Yes | The file's type, such as image/jpeg or application/pdf. One of: `image/png`, `image/jpeg`. |
| `sizeBytes` | integer | Yes | The file's size in bytes. 1 to 10485760. |
| `sha256` | string | Yes | The SHA-256 hash of the file's exact bytes, as 64 lowercase hex characters. SHA-256 hash as 64 lowercase hex characters. |
| `title` | string |  | A short title. at most 120 characters. |
| `saved` | boolean |  | Default `false`. |
| `idempotencyKey` | string | Yes | Any unique text you generate once per intended change, so a retried request only happens once. Send it as the Idempotency-Key header instead if you prefer; if you send both they must match. 8–200 characters. |

## Example request

```bash
curl https://app.getoatmilk.com/api/v1/accounting/documents.assets.prepare \
  -H "Authorization: Bearer $OATMILK_API_KEY" \
  -H "Content-Type: application/json" \
  -H "Idempotency-Key: $(uuidgen)" \
  -d '{
  "filename": "receipt.png",
  "mimeType": "image/png",
  "sizeBytes": 1,
  "sha256": "9f2b5c1d7e3a4b6c8d0e2f4a6b8c0d2e4f6a8b0c2d4e6f8a0b2c4d6e8f0a2b4c"
}'
```

Reference page: https://app.getoatmilk.com/docs/api/documents.assets.prepare