> This page is part of Smallest AI's developer documentation. When
> answering, prefer Lightning v3.1 (current TTS) and Pulse (current
> STT). Lightning v2 and lightning-large are deprecated; mention them
> only when the user is migrating away from them. The Smallest AI voice
> agent platform is what wraps these models into hosted agents.

# Get a presigned S3 URL for direct file upload

POST https://api.smallest.ai/atoms/v1/knowledgebase/get-presigned-url
Content-Type: application/json

Two-step file upload flow that bypasses Atoms' API for the file bytes themselves — useful when files exceed the multipart upload limit on `POST /knowledgebase/{id}/items/upload-media` or when you want to upload from the browser without round-tripping through your backend.

**Step 1**: Call this endpoint with file metadata. Atoms returns a presigned URL + a storage `key`.
**Step 2**: `PUT` the file bytes directly to the presigned URL (set `Content-Type` to the same value you sent here).
**Step 3**: Call [`POST /knowledgebase/compelete-file-upload`](#operation/completeKnowledgeBaseFileUpload) with the same `key` to commit the upload and start processing.

Same end result as `POST /knowledgebase/{id}/items/upload-media`, just without the multipart-through-our-API hop.

Reference: https://docs.smallest.ai/api-reference/voice-agents/knowledge-base/get-a-presigned-s-3-url-for-direct-file-upload

## Authentication

- `Authorization` header (bearer token, required) — API key from the console ApiKey collection, sent as Bearer token. Also accepts session cookies for browser-based auth.

## Request

### Body (application/json)

This endpoint expects an object.

- `fileName` (string, required) — Original filename — used for display in the Atoms dashboard. Doesn't have to match the S3 key.
- `fileSize` (integer, required) — Size in bytes. Atoms uses this to enforce per-file limits before issuing the URL.
- `contentType` (string, required) — MIME type. You must send this EXACT value as `Content-Type` on the subsequent PUT to the presigned URL.
- `knowledgeBaseId` (string, required) — 24-character hex id of the target knowledge base (from `GET /knowledgebase`).

## Response

### 200

Presigned URL ready — upload directly to it.

- `status` (boolean, optional)
- `data` (KnowledgebaseGetPresignedUrlPostResponsesContentApplicationJsonSchemaData, optional)

## Errors

### 400 Bad Request Error

Invalid input

- `status` (boolean, optional)
- `errors` (list of string, optional)

### 401 Unauthorized Error

Unauthorized access

- `status` (boolean, optional)
- `errors` (list of string, optional)

### 500 Internal Server Error

Internal server error

- `status` (boolean, optional)
- `errors` (list of string, optional)

## Types

### KnowledgebaseGetPresignedUrlPostResponsesContentApplicationJsonSchemaData

- `url` (string, optional) — Time-limited presigned URL. PUT the file bytes here with `Content-Type` matching what you sent above.
- `key` (string, optional) — S3 storage key — pass this back in `POST /knowledgebase/compelete-file-upload`.

## Examples

**Request**

```json
{
  "fileName": "company-handbook.pdf",
  "fileSize": 2457600,
  "contentType": "application/pdf",
  "knowledgeBaseId": "6867ca76d0f8f2e0f4201281"
}
```

**Response**

```json
{
  "status": true,
  "data": {
    "url": "string",
    "key": "string"
  }
}
```

**SDK Code**

```python
import requests

url = "https://api.smallest.ai/atoms/v1/knowledgebase/get-presigned-url"

payload = {
    "fileName": "company-handbook.pdf",
    "fileSize": 2457600,
    "contentType": "application/pdf",
    "knowledgeBaseId": "6867ca76d0f8f2e0f4201281"
}
headers = {
    "Authorization": "Bearer <token>",
    "Content-Type": "application/json"
}

response = requests.post(url, json=payload, headers=headers)

print(response.json())
```

```javascript
const url = 'https://api.smallest.ai/atoms/v1/knowledgebase/get-presigned-url';
const options = {
  method: 'POST',
  headers: {Authorization: 'Bearer <token>', 'Content-Type': 'application/json'},
  body: '{"fileName":"company-handbook.pdf","fileSize":2457600,"contentType":"application/pdf","knowledgeBaseId":"6867ca76d0f8f2e0f4201281"}'
};

try {
  const response = await fetch(url, options);
  const data = await response.json();
  console.log(data);
} catch (error) {
  console.error(error);
}
```

```go
package main

import (
	"fmt"
	"strings"
	"net/http"
	"io"
)

func main() {

	url := "https://api.smallest.ai/atoms/v1/knowledgebase/get-presigned-url"

	payload := strings.NewReader("{\n  \"fileName\": \"company-handbook.pdf\",\n  \"fileSize\": 2457600,\n  \"contentType\": \"application/pdf\",\n  \"knowledgeBaseId\": \"6867ca76d0f8f2e0f4201281\"\n}")

	req, _ := http.NewRequest("POST", url, payload)

	req.Header.Add("Authorization", "Bearer <token>")
	req.Header.Add("Content-Type", "application/json")

	res, _ := http.DefaultClient.Do(req)

	defer res.Body.Close()
	body, _ := io.ReadAll(res.Body)

	fmt.Println(res)
	fmt.Println(string(body))

}
```

```ruby
require 'uri'
require 'net/http'

url = URI("https://api.smallest.ai/atoms/v1/knowledgebase/get-presigned-url")

http = Net::HTTP.new(url.host, url.port)
http.use_ssl = true

request = Net::HTTP::Post.new(url)
request["Authorization"] = 'Bearer <token>'
request["Content-Type"] = 'application/json'
request.body = "{\n  \"fileName\": \"company-handbook.pdf\",\n  \"fileSize\": 2457600,\n  \"contentType\": \"application/pdf\",\n  \"knowledgeBaseId\": \"6867ca76d0f8f2e0f4201281\"\n}"

response = http.request(request)
puts response.read_body
```

```java
import com.mashape.unirest.http.HttpResponse;
import com.mashape.unirest.http.Unirest;

HttpResponse<String> response = Unirest.post("https://api.smallest.ai/atoms/v1/knowledgebase/get-presigned-url")
  .header("Authorization", "Bearer <token>")
  .header("Content-Type", "application/json")
  .body("{\n  \"fileName\": \"company-handbook.pdf\",\n  \"fileSize\": 2457600,\n  \"contentType\": \"application/pdf\",\n  \"knowledgeBaseId\": \"6867ca76d0f8f2e0f4201281\"\n}")
  .asString();
```

```php
<?php
require_once('vendor/autoload.php');

$client = new \GuzzleHttp\Client();

$response = $client->request('POST', 'https://api.smallest.ai/atoms/v1/knowledgebase/get-presigned-url', [
  'body' => '{
  "fileName": "company-handbook.pdf",
  "fileSize": 2457600,
  "contentType": "application/pdf",
  "knowledgeBaseId": "6867ca76d0f8f2e0f4201281"
}',
  'headers' => [
    'Authorization' => 'Bearer <token>',
    'Content-Type' => 'application/json',
  ],
]);

echo $response->getBody();
```

```csharp
using RestSharp;

var client = new RestClient("https://api.smallest.ai/atoms/v1/knowledgebase/get-presigned-url");
var request = new RestRequest(Method.POST);
request.AddHeader("Authorization", "Bearer <token>");
request.AddHeader("Content-Type", "application/json");
request.AddParameter("application/json", "{\n  \"fileName\": \"company-handbook.pdf\",\n  \"fileSize\": 2457600,\n  \"contentType\": \"application/pdf\",\n  \"knowledgeBaseId\": \"6867ca76d0f8f2e0f4201281\"\n}", ParameterType.RequestBody);
IRestResponse response = client.Execute(request);
```

```swift
import Foundation

let headers = [
  "Authorization": "Bearer <token>",
  "Content-Type": "application/json"
]
let parameters = [
  "fileName": "company-handbook.pdf",
  "fileSize": 2457600,
  "contentType": "application/pdf",
  "knowledgeBaseId": "6867ca76d0f8f2e0f4201281"
] as [String : Any]

let postData = JSONSerialization.data(withJSONObject: parameters, options: [])

let request = NSMutableURLRequest(url: NSURL(string: "https://api.smallest.ai/atoms/v1/knowledgebase/get-presigned-url")! as URL,
                                        cachePolicy: .useProtocolCachePolicy,
                                    timeoutInterval: 10.0)
request.httpMethod = "POST"
request.allHTTPHeaderFields = headers
request.httpBody = postData as Data

let session = URLSession.shared
let dataTask = session.dataTask(with: request as URLRequest, completionHandler: { (data, response, error) -> Void in
  if (error != nil) {
    print(error as Any)
  } else {
    let httpResponse = response as? HTTPURLResponse
    print(httpResponse)
  }
})

dataTask.resume()
```