> 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/voice-agents/api-reference/knowledge-base/get-a-presigned-s-3-url-for-direct-file-upload ## OpenAPI Specification ```yaml openapi: 3.1.0 info: title: atoms version: 1.0.0 paths: /knowledgebase/get-presigned-url: post: operationId: get-a-presigned-s-3-url-for-direct-file-upload summary: Get a presigned S3 URL for direct file upload description: > 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. tags: - knowledgeBase parameters: - name: Authorization in: header description: >- API key from the console ApiKey collection, sent as Bearer token. Also accepts session cookies for browser-based auth. required: true schema: type: string responses: '200': description: Presigned URL ready — upload directly to it. content: application/json: schema: $ref: >- #/components/schemas/Knowledge Base_getAPresignedS3UrlForDirectFileUpload_Response_200 '400': description: Invalid input content: application/json: schema: $ref: '#/components/schemas/BadRequestErrorResponse' '401': description: Unauthorized access content: application/json: schema: $ref: '#/components/schemas/UnauthorizedErrorResponse' '500': description: Internal server error content: application/json: schema: $ref: '#/components/schemas/InternalServerErrorResponse' requestBody: content: application/json: schema: type: object properties: fileName: type: string description: >- Original filename — used for display in the Atoms dashboard. Doesn't have to match the S3 key. fileSize: type: integer description: >- Size in bytes. Atoms uses this to enforce per-file limits before issuing the URL. contentType: type: string description: >- MIME type. You must send this EXACT value as `Content-Type` on the subsequent PUT to the presigned URL. knowledgeBaseId: type: string description: >- 24-char hex ObjectId of the target knowledge base (from `GET /knowledgebase`). required: - fileName - fileSize - contentType - knowledgeBaseId servers: - url: https://api.smallest.ai/atoms/v1 description: Production server components: schemas: KnowledgebaseGetPresignedUrlPostResponsesContentApplicationJsonSchemaData: type: object properties: url: type: string format: uri description: >- Time-limited presigned URL. PUT the file bytes here with `Content-Type` matching what you sent above. key: type: string description: >- S3 storage key — pass this back in `POST /knowledgebase/compelete-file-upload`. title: >- KnowledgebaseGetPresignedUrlPostResponsesContentApplicationJsonSchemaData Knowledge Base_getAPresignedS3UrlForDirectFileUpload_Response_200: type: object properties: status: type: boolean data: $ref: >- #/components/schemas/KnowledgebaseGetPresignedUrlPostResponsesContentApplicationJsonSchemaData title: Knowledge Base_getAPresignedS3UrlForDirectFileUpload_Response_200 BadRequestErrorResponse: type: object properties: status: type: boolean errors: type: array items: type: string title: BadRequestErrorResponse UnauthorizedErrorResponse: type: object properties: status: type: boolean errors: type: array items: type: string title: UnauthorizedErrorResponse InternalServerErrorResponse: type: object properties: status: type: boolean errors: type: array items: type: string title: InternalServerErrorResponse securitySchemes: BearerAuth: type: http scheme: bearer description: >- API key from the console ApiKey collection, sent as Bearer token. Also accepts session cookies for browser-based auth. ``` ## Examples **Request** ```json { "fileName": "marketing-presentation.pptx", "fileSize": 5242880, "contentType": "application/vnd.openxmlformats-officedocument.presentationml.presentation", "knowledgeBaseId": "5f8d04b3a1c2e45b6d7f9a12" } ``` **Response** ```json { "status": true, "data": { "url": "https://s3.amazonaws.com/atoms-uploads/5f8d04b3a1c2e45b6d7f9a12/marketing-presentation.pptx?X-Amz-Algorithm=AWS4-HMAC-SHA256&X-Amz-Credential=AKIAIOSFODNN7EXAMPLE%2F20240601%2Fus-east-1%2Fs3%2Faws4_", "key": "uploads/5f8d04b3a1c2e45b6d7f9a12/marketing-presentation.pptx" } } ``` **SDK Code** ```python import requests url = "https://api.smallest.ai/atoms/v1/knowledgebase/get-presigned-url" payload = { "fileName": "marketing-presentation.pptx", "fileSize": 5242880, "contentType": "application/vnd.openxmlformats-officedocument.presentationml.presentation", "knowledgeBaseId": "5f8d04b3a1c2e45b6d7f9a12" } headers = { "Authorization": "Bearer ", "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 ', 'Content-Type': 'application/json'}, body: '{"fileName":"marketing-presentation.pptx","fileSize":5242880,"contentType":"application/vnd.openxmlformats-officedocument.presentationml.presentation","knowledgeBaseId":"5f8d04b3a1c2e45b6d7f9a12"}' }; 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\": \"marketing-presentation.pptx\",\n \"fileSize\": 5242880,\n \"contentType\": \"application/vnd.openxmlformats-officedocument.presentationml.presentation\",\n \"knowledgeBaseId\": \"5f8d04b3a1c2e45b6d7f9a12\"\n}") req, _ := http.NewRequest("POST", url, payload) req.Header.Add("Authorization", "Bearer ") 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 ' request["Content-Type"] = 'application/json' request.body = "{\n \"fileName\": \"marketing-presentation.pptx\",\n \"fileSize\": 5242880,\n \"contentType\": \"application/vnd.openxmlformats-officedocument.presentationml.presentation\",\n \"knowledgeBaseId\": \"5f8d04b3a1c2e45b6d7f9a12\"\n}" response = http.request(request) puts response.read_body ``` ```java import com.mashape.unirest.http.HttpResponse; import com.mashape.unirest.http.Unirest; HttpResponse response = Unirest.post("https://api.smallest.ai/atoms/v1/knowledgebase/get-presigned-url") .header("Authorization", "Bearer ") .header("Content-Type", "application/json") .body("{\n \"fileName\": \"marketing-presentation.pptx\",\n \"fileSize\": 5242880,\n \"contentType\": \"application/vnd.openxmlformats-officedocument.presentationml.presentation\",\n \"knowledgeBaseId\": \"5f8d04b3a1c2e45b6d7f9a12\"\n}") .asString(); ``` ```php request('POST', 'https://api.smallest.ai/atoms/v1/knowledgebase/get-presigned-url', [ 'body' => '{ "fileName": "marketing-presentation.pptx", "fileSize": 5242880, "contentType": "application/vnd.openxmlformats-officedocument.presentationml.presentation", "knowledgeBaseId": "5f8d04b3a1c2e45b6d7f9a12" }', 'headers' => [ 'Authorization' => 'Bearer ', '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 "); request.AddHeader("Content-Type", "application/json"); request.AddParameter("application/json", "{\n \"fileName\": \"marketing-presentation.pptx\",\n \"fileSize\": 5242880,\n \"contentType\": \"application/vnd.openxmlformats-officedocument.presentationml.presentation\",\n \"knowledgeBaseId\": \"5f8d04b3a1c2e45b6d7f9a12\"\n}", ParameterType.RequestBody); IRestResponse response = client.Execute(request); ``` ```swift import Foundation let headers = [ "Authorization": "Bearer ", "Content-Type": "application/json" ] let parameters = [ "fileName": "marketing-presentation.pptx", "fileSize": 5242880, "contentType": "application/vnd.openxmlformats-officedocument.presentationml.presentation", "knowledgeBaseId": "5f8d04b3a1c2e45b6d7f9a12" ] 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() ```