CORS Preflight Request Failing
Frontend makes a complex request (POST with JSON body) to API, preflight OPTIONS request fails with 403 or 405 error. Actual request never sent because browser stops at preflight check. Simple GET requests work but POST/PUT/DELETE fail.
CORS configuration exists but doesn't handle preflight requests correctly.
Error Messages You Might See
Common Causes
- OPTIONS method not allowed in CORS configuration
- CORS headers missing or misconfigured: Access-Control-Allow-Methods
- Custom headers not whitelisted: Access-Control-Allow-Headers
- Credentials not allowed: Access-Control-Allow-Credentials missing
- Origin not in allowed list for preflight
How to Fix It
Ensure OPTIONS requests are handled and return 200 with CORS headers. Configure: Access-Control-Allow-Methods: GET, POST, PUT, DELETE, OPTIONS. Access-Control-Allow-Headers: Content-Type, Authorization. Access-Control-Allow-Origin: * (or specific domain). Access-Control-Allow-Credentials: true (only if credentials needed). Test preflight: curl -i -X OPTIONS http://api.example.com/endpoint
Real developers can help you.
Alvin Voo
I’ve watched the tech landscape evolve over the last decade—from the structured days of Java Server Pages to the current "wild west" of Agentic-driven development. While AI can "vibe" a frontend into existence, I specialize in the architecture that keeps it from collapsing.
My expertise lies in the critical backend infrastructure: the parts that must be fast, secure, and scalable. I thrive on high-pressure environments, such as when I had only three weeks to architect and launch an Ethereum redemption system with minimal prior crypto knowledge, turning it into a major revenue stream.
What I bring to your project:
Forensic Debugging: I don't just "patch" bugs; I use tools like Datadog and Explain Analyzers to map out bottlenecks and resolve root causes—like significantly reducing memory usage by optimizing complex DB joins.
Full-Stack Context: Deep experience in Node.js and React, ensuring backends play perfectly with mobile and web teams.
Sanity in the Age of AI: I bridge the gap between "best practices" and modern speed, ensuring your project isn't just built fast, but built to last.
Daniel Vázquez
Software Engineer with over 10 years of experience on Startups, Government, big tech industry & consulting.
Rudra Bhikadiya
I build and fix web apps across Next.js, Node.js, and DBs.
Comfortable jumping into messy code, broken APIs, and mysterious bugs.
If your project works in theory but not in reality, I help close that gap.
Jaime Orts-Caroff
I'm a Senior Android developer, open to work in various fields
Costea Adrian
Embedded Engineer specilizing in perception systems. Latest project was a adas camera calibration system.
Victor Denisov
Developer
Dor Yaloz
SW engineer with 6+ years of experience,
I worked with React/Node/Python
did projects with React+Capacitor.js for ios
Supabase expert
Antriksh Narang
5 years+ Experienced Dev (Specially in Web Development), can help in python, javascript, react, next.js and full stack web dev technologies.
Yovel Cohen
I got a lot of experience in building Long-horizon AI Agents in production, Backend apps that scale to millions of users and frontend knowledge as well.
Jen Jacobsen
I’m a Full-Stack Developer with over 10 years of experience building modern web and mobile applications. I enjoy working across the full product lifecycle — turning ideas into real, well-built products that are intuitive for users and scalable for businesses.
I particularly enjoy building mobile apps, modern web platforms, and solving complex technical problems in a way that keeps systems clean, reliable, and easy to maintain.
You don't need to be technical. Just describe what's wrong and a verified developer will handle the rest.
Get HelpFrequently Asked Questions
What is CORS preflight?
For non-simple requests (POST with JSON, custom headers), browser sends OPTIONS first to check if request allowed. If OPTIONS fails, actual request never sent.
How to allow all origins?
Access-Control-Allow-Origin: * allows all. For credentials, use specific domain: Access-Control-Allow-Origin: https://example.com
What headers must be allowed?
At minimum: Content-Type. Also: Authorization if using tokens. Declare with: Access-Control-Allow-Headers: Content-Type, Authorization