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Supabase CORS Settings Complete Guide 2025

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What In The World Is CORS?

Cross origin resource sharing (yes, the mouthful) lets a browser ask a server for permission before moving data across a different domain. That tiny dance keeps malicious websites from grabbing the requested resource without a nod of approval.

If you need a step-by-step walkthrough with updated screenshots, our in-house Supabase CORS Settings Complete Guide 2025 covers every dashboard screen and CLI flag in even greater detail. For a concise alternative walkthrough, the community-driven guide on how to configure CORS in Supabase explains each flag with copy-paste snippets.

Why Should Developers Care?

If your frontend runs on https://myapp.com and your Supabase api sits on https://db.techventures.org, the browser sees two origin values. Without tidy cors headers, you’ll stare at a big, red error message that claims, “This request has been blocked by CORS policy.”

Considering whether to stick with Supabase or evaluate other options like Xano for your 2025 stack? The detailed comparison Xano vs Supabase – Which No-Code Backend Is Best in 2025? weighs performance, pricing, and CORS handling side by side.

To understand the broader ecosystem behind that techventures.org namespace, you can visit the TechVentures homepage for additional context.

Meet The Star: supabase cors settings

One switch inside the supabase dashboard controls the first layer. Yet the real magic happens in code, where you craft custom cors headers for edge functions and regular REST calls.

Key Vocabulary In Plain English

• access control allow origin: says which domains get through
• access control allow headers: lists which custom headers ride along
• access control allow methods: whitelists each HTTP method like GET or DELETE
• access control allow: the family term folks use for all three lines above
• cors policy: the whole rulebook
• preflight request: an OPTIONS request the browser sends to double-check safety

Opening The Supabase Dashboard

Click Settings → API → CORS. Add your allowed origins such as https://myapp.com, http://localhost:3000, and a wildcard if you dare. Hit Save; then double check the list. That simple screen stops many cors issues before you write a single line of code. If you’re wondering exactly what happens under the hood, the official Supabase Functions CORS documentation breaks down the header logic used by the platform.

When Edge Power Beats Dashboard Clicks

Supabase edge functions give you super-fine knobs. Every function runs close to users, so response time stays zippy. You can insert custom access control allow lines, rate-limit, or even tailor rules per authorization role.

Sample Function For Fast Readers

// ./functions/hello-cors/index.ts
import { serve } from 'https://edge.com/foo/mod.ts'
import { corsHeaders } from 'https://edge.com/foo/cors.ts'

serve(async (req) => {
  const origin = req.headers.get('origin')  // watch origin http value
  const allowed = ['https://myapp.com', 'http://localhost:3000']

  let headers = { ...corsHeaders }          // base cors headers
  if (allowed.includes(origin)) {
    headers['access-control-allow-origin'] = origin
  }

  const data = { hello: 'world' }           // const data payload
  return new Response(JSON.stringify(data), {
    headers,
    status: 200
  })
})

That snippet shows access control allow origin, the content type set to application/json, and a clean new response object.

Breaking Down The Headers

  1. content-type: application/json tells the browser what’s coming.
  2. x-client-info and x-requested-with are extra headers folks add for auth or tracing.
  3. Every new response should echo the origin when you allow it.

The Famous Preflight

The browser console reveals the silent OPTIONS request. If your function does not return headers like access-control-allow-methods: POST, GET, the error pops. So answer the preflight request with the same access control allow lines.

Watching The Network Tab

Open browser developer tools, hop to the network tab, click any row, and peek at Headers. You’ll see access-control-allow-headers, access-control-allow-origin, content-type. Missing one? Cors error.

A Tiny Next.js Twist

Next.js API routes live under another origin during local development (http://localhost:3000). Add that to your allowed origins list and mirror the same cors headers in your supabase edge functions. No magic, just symmetry.

Netlify, Vercel, And Friends

Netlify’s proxy or Vercel’s rewrites can inject their own origin http value. Again, add their preview URL to allowed origins or you’ll get a blocked message.

Flutter Web, Too!

For supabase flutter web cors, set fetchMode: 'cors' in the client options and trust the same access control allow lines on the server side.

Handling Auth Tokens

Send authorization: Bearer ... and apikey: ... along. Make sure authorization appears in access control allow headers and content type stays application/json. Forget that, and the error log will howl.

When You Really Must Handle CORS Manually

Sometimes you have to handle cors manually — maybe a partner server that returns static XML. Pipe the call through your own edge functions with the access control allow origin you trust.

Common Error Messages

“Request header field x-client-info is not allowed.”
“No ‘access-control-allow-origin’ header present.”

Each error message points to a missing word in the headers. Add it, redeploy, and watch the new response.

Quick Curl Test

curl -I -H "Origin: https://myapp.com" 
     -H "X-Client-Info: demo" 
     https://db.techventures.org/functions/v1/hello-cors

Look for a status 200 and the trio of access control allow lines in the response.

Checklist Before Shipping

  • Allowed origins include prod, staging, and localhost.
  • All content type values match (application/json).
  • Access control allow headers lists authorization, content-type, x-client-info.
  • Access control allow methods covers every method you plan to use.
  • Edge functions send the same headers on every new response.

Security Nudge

Too many * wildcards open doors. Limit to trusted domains; that’s real control. Rotate auth keys. Log every suspicious request for later study.

Small Digression On JSON Bugs

If you forget JSON.stringify(data), the browser might treat your response as plain text. That sneaky error can mimic a cors error. The content type flag matters.

Local Development Pitfalls

People often swap https for http during tests. The origin string changes, so the server might reject it. Keep both origin http and https addresses on your allowed origins list.

Deleting Old Rules

A stale rule can stay in cache. After you delete a domain, clear CDN cache or you’ll see mixed status codes. Another silent mistake.

A Mini FAQ

Q: Can I wildcard sub-domains?
A: Yes, https://*.myapp.com under access control allow origin works, but tread carefully.

Q: Where do I put x-client-info?
A: Add it to access control allow headers and send it from the client.

Final Thought

Caring for cors feels like watering plants — small, steady, and sometimes messy. Yet once the settings are correct, your frontend talks to the server with no drama, and users never see an ugly error again. Happy coding, and may every new response carry the perfect headers.

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