FastAPI for AI Engineers - Part 8: Uploading Files with FastAPI

In the previous article, we learned how to secure our APIs using JWT Authentication and protect routes from unauthorized access. Now let's explore another feature used in almost every AI application— file uploads . If you've built applications like ChatGPT, document Q&A systems, resume analyzers, legal contract reviewers, or medical report analyzers, one thing is common across all of them: The user uploads a file. Without file uploads, there is nothing for the AI model to process. If you haven't read the previous article, check it out first to continue the series: Protecting routes with JWT Tokens Why Do We Need File Uploads? Consider some popular AI applications: ChatGPT allows you to upload PDFs and images. Resume analyzers require your resume. Legal AI assistants analyze contracts. Medical AI systems analyze lab reports. RAG applications build knowledge bases from documents. The workflow usually looks like this: User │ ▼ Upload File │ ▼ FastAPI │ ▼ Save / Read File │ ▼ Process using AI FastAPI makes uploading files extremely simple. Installing Required Package FastAPI uses python-multipart to process uploaded files. Install it using: pip install python-multipart Your First File Upload API FastAPI provides two important classes: File UploadFile Let's import them. from fastapi import FastAPI , File , UploadFile app = FastAPI () Creating the Upload Endpoint @app.post ( " /upload " ) def upload_file ( file : UploadFile ): return { " filename " : file . filename } Run the application. Open Swagger UI. Click POST /upload . You'll notice FastAPI automatically provides a file picker. Upload a file. Response: { "filename" : "resume.pdf" } Our API successfully received the uploaded file. Understanding UploadFile You might wonder: Why didn't we simply use a string or bytes? FastAPI provides the UploadFile class because it contains useful information about the uploaded file. Some commonly used attributes are: file . filename Returns: resume.pdf file . content_type Returns: a