AI Agent CORS Setup 2026

The frontend happily calls the Agent API, and the browser throws a CORS error. It's not the Agent's fault—it's that CORS isn't configured properly.

💡 What You Will Learn

The frontend happily calls the Agent API, and the browser throws a CORS error. It's not the Agent's fault—it's that CORS isn't configured properly.

📜 Table of Contents

• CORSWhat Is
• Summary

CORSWhat Is

from fastapi.middleware.cors import CORSMiddleware

app.add_middleware(
    CORSMiddleware,
    allow_origins=["https://app.com"],
    allow_methods=["*"],
    allow_headers=["*"],
)

Summary

origins = [
    "https://app.example.com",
    "https://admin.example.com",
]

app.add_middleware(
    CORSMiddleware,
    allow_origins=origins,  # ["*"]
    allow_credentials=True,
    allow_methods=["GET", "POST"],
    allow_headers=["Authorization", "Content-Type"],
)