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rob--w/cors-anywhere

★ 9,369JavaScriptAudience · developerComplexity · 2/5Setup · easy

TLDR

A small Node.js proxy server that adds the CORS headers browsers need, so your web page can fetch data from any domain, self-host your own locked-down instance instead of using the public demo.

Mindmap

mindmap
  root((CORS Anywhere))
    What it does
      Proxy requests
      Add CORS headers
      Forward responses
    Config options
      Allowed origins
      Rate limits
      Strip cookies
    Use cases
      Local dev proxy
      Third-party API access
      Locked-down instance
    Caution
      Public demo restricted
      Self-host recommended
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Things people build with this

USE CASE 1

Route browser requests to a third-party API that does not send CORS headers so your web page can read the response.

USE CASE 2

Lock down a proxy instance to only allow requests from your own domain and set per-IP rate limits.

USE CASE 3

Use as a local development proxy so your frontend can reach external APIs without browser security blocks.

Tech stack

JavaScriptNode.js

Getting it running

Difficulty · easy Time to first run · 5min

Lock down allowedOrigins before deploying publicly or anyone can route traffic through your instance.

License terms not stated in the explanation.

In plain English

CORS Anywhere is a small Node.js server that acts as a middleman between a web browser and another website. It exists to solve a specific browser security restriction: by default, a web page is not allowed to make requests to a different domain. This restriction is called the same-origin policy, and it prevents, for example, a page at example.com from directly fetching data from api.otherdomain.com. CORS (Cross-Origin Resource Sharing) is the mechanism that websites use to explicitly permit such requests. The way CORS Anywhere works is simple. You start the server on your own machine or hosting provider, and then prefix any URL you want to reach with the server's address. The proxy forwards your request to the target URL and adds the necessary CORS permission headers to the response before passing it back. This makes the browser treat the response as if it came from your own domain, allowing the page to read it. You can configure the server in several ways. You can restrict which origins are allowed to use it, which prevents strangers from routing their own requests through your instance. You can require specific request headers to block direct browser visits. You can also strip cookies from outgoing requests, set rate limits, and customize most other aspects of how the proxy behaves. There is a public demo server available, but as of early 2021 it requires an opt-in and has strict rate limits. The author recommends running your own instance if you have any real traffic, and locking it down to only the origins you control so it does not become an open proxy accessible to anyone on the internet. The project is written in JavaScript for Node.js and is straightforward to deploy. It can be run locally or on platforms like Heroku with minimal configuration.

Copy-paste prompts

Prompt 1
I want to run my own CORS Anywhere server restricted to only my frontend domain. Show me the Node.js startup code that sets allowedOrigins and blocks all other callers.
Prompt 2
My React app needs to call a REST API that rejects CORS. Show me how to prefix the API URL with my CORS Anywhere instance and handle the response in a fetch call.
Prompt 3
Deploy a rate-limited CORS Anywhere instance to Heroku that allows only my frontend origin with a cap of 200 requests per hour per IP.
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