File uploader

What is 'Upload Failed'?

'Upload Failed' (or “Error: Upload Failed”) is an error message that appears when attempting to post or upload images on 4chan or its extensions (e.g., 4chan-X).
This message is a “generic failure notification” displayed when postings are blocked for specific reasons.
In other words, it suggests that the file transfer has not only been interrupted but that multiple factors could be involved, such as posting restrictions, authentication issues, or interference from extensions.

Initial Troubleshooting Steps

Here are the first items to check when encountering “Upload Failed”.

  • Clear browser cache and cookies, then reload
  • [Recommended] Try another browser (or private mode/ incognito mode)
  • Change your network (e.g., WiFi ↔ mobile connection, switch providers)
  • Check if your IP address is blocked (more on this later)

Many cases are resolved by these basic checks, but if not, you will need to explore deeper causes.

Common Causes and In-Depth Analysis

Interference from Extensions or User Scripts

Extensions like AdBlock, uBlock, script control extensions, and security extensions can block 4chan’s posting scripts or image upload processes. Especially among users with 4chan-X installed, there have been multiple reports stating that "posts could be made by disabling extensions." Try turning off your extensions and see if you can post.

CAPTCHA Authentication Issues / CORS Policy Restrictions

A CAPTCHA verification may be required during posting, but it can sometimes fail to load correctly in the browser or be blocked due to CORS (Cross-Origin Resource Sharing) restrictions.
Press F12 to open the developer tools and check the network for errors such as the following:

“Access to fetch at 'https://sys.4channel.org/captcha?board=vp' … has been blocked by CORS policy”
In such cases, using a different browser or disabling extensions may resolve the issue.

IP Blocking / ISP-Level Restrictions

4chan may collectively block certain IP addresses or ISPs (Internet Service Providers).
Your IP could be restricted due to the misconduct of other users using the same ISP.
In this case, the following actions can be effective:

  • Use a VPN to access from a different IP (but be aware that the VPN may already be blocked, so try multiple servers)
  • Switch to a mobile connection to post
  • Restart your router to gain a new dynamic IP if possible
  • Contact your provider to request an IP change / submit a request for unblocking

Issues with Content, File Formats, or Sizes

Occasionally, the reason might be that the file format, extension, or size you're trying to upload is not allowed.
Changing the file format, compressing the file, or using another image uploader to share the URL can help avoid this (external services are often used to post image URLs in specialized browsers).

Alternative Method: Using External Uploaders

When the posting feature on 4chan doesn't work properly, hosting images with an external uploader instead of using their upload function can be effective.
A tool I would like to recommend is the free and easy-to-use web tool **UploadF (uploadf.com)**.

Main features of UploadF:

  • Can be used on both PC and mobile
  • Easy upload via drag and drop
  • Can upload up to 100 files simultaneously
  • Storage periods from 1 month to indefinite (extendable)
  • Ability to delete files individually
  • Supports many file types, with safety considerations

The usage is simple. Upload an image to UploadF and paste the generated URL into the 4chan posting screen.
If there are issues with the 4chan posting feature itself, this method serves as a very effective backup.

(Example)

  • Send an image to UploadF → Copy the generated image URL
  • Paste the URL into the 4chan posting screen
  • Execute the post along with the text

Conclusion: Suspect Extensions and IP Restrictions First

'Upload Failed' is not just a file transfer error; it can involve multiple factors such as posting, authentication, and IP restrictions. Start by questioning browser extensions, CAPTCHA, and basic elements such as a different network or VPN. If you are still unable to post, using an external uploader like UploadF to directly paste a URL can be a very powerful workaround.

If this method does not resolve the issue, please let us know your environment (browser name / internet connection / extensions, etc.), and we can provide more specific measures.


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