Having trouble logging into ChatGPT with the error “Unexpected token ‘<‘, ‘<!DOCTYPE’… is not valid JSON”? Learn how to fix “unexpected token error in ChatGPT login issue easily!
If you’re trying to log in to ChatGPT and receive the error message:
“Unexpected token ‘<‘, ‘<!DOCTYPE’… is not valid JSON”
you may feel confused or frustrated. This message appears technical, but it usually points to a very fixable issue. It doesn’t mean there’s a problem with ChatGPT itself or your account. Instead, this error is most commonly caused by a network-related problem that interrupts proper communication between your device and the ChatGPT servers.
This guide explains why the error appears, what it means, and how to solve it step by step using simple methods that work across devices.
ChatGPT Login Error: “<!DOCTYPE… is Not Valid JSON” Error on ChatGPT
The error you’re encountering occurs when your browser or device is expecting a response in JSON format—typically a lightweight data format used by APIs like ChatGPT’s backend. However, instead of receiving the expected JSON data, your device receives HTML code, often beginning with <!DOCTYPE html>. That first character (<) causes the browser or script to crash with an “unexpected token” error because it’s interpreting an HTML document as JSON.
This issue doesn’t happen randomly. It typically occurs during login or while ChatGPT is initializing authentication processes—when network communication must be smooth and consistent.
This problem has been seen across various platforms, but especially with web-based access via browsers or mobile networks. Fortunately, you can resolve it by addressing the root cause: network interference or misrouting.
What “Unexpected Token ‘<‘, <!DOCTYPE… Is Not Valid JSON” Meaning
When applications like ChatGPT connect to their backend services, they expect structured responses in JSON format. These are necessary for operations like login validation, session creation, and user authentication. A successful login would typically involve multiple background JSON requests that establish your session.
However, if a network issue causes the server response to return something other than JSON—most often HTML, which is formatted for web browsers—the browser attempts to parse it as JSON and fails. HTML content typically starts with <!DOCTYPE html>, which immediately causes the parser to reject the input.
So the error message:
“Unexpected token ‘<‘, <!DOCTYPE… is not valid JSON”
means your browser received a webpage or HTML document when it was expecting structured JSON data. This mismatch is interpreted as a critical error in parsing, and the login process halts.
Why This Error Appears During ChatGPT Login
This error is especially common during login attempts for several reasons:
- Authentication Requires Real-Time Data Exchange:
Logging into ChatGPT involves several steps behind the scenes, including exchanging secure tokens, verifying your credentials, and initializing your user session. These steps all rely on uninterrupted and accurate data exchanges. - APIs Expect Clean JSON Responses:
If even one of these steps receives an unexpected HTML response—possibly due to network redirection or a faulty response—it will crash and produce the error in question. - Redirection by ISP or Network Interruption:
If your network redirects you to a login page, throttles content, or injects headers, it may send you HTML content. ChatGPT cannot interpret that in the login pipeline and throws the error. - VPNs, DNS Services, and Proxies:
If you are connected through a VPN or using a custom DNS service, there’s a chance that your requests are being routed incorrectly, leading to invalid or altered server responses.
The bottom line: this error appears because your login request is either not reaching the correct server or not receiving the expected format due to network-related interference.
Why ChatGPT Shows ‘Unexpected Token’ JSON Error
Let’s look at the most frequent reasons why your browser or device is receiving HTML instead of JSON:
Mobile Networks and Hotspots
Many users who connect through mobile data report this issue. Some mobile ISPs modify content, compress traffic, or redirect requests to filter content or manage bandwidth. This can break JSON requests and return fallback HTML error pages instead.
Faulty or Overprotective VPNs
Virtual Private Networks (VPNs) can alter or block requests to ChatGPT’s servers. While they protect your privacy, they can also reroute traffic through misconfigured servers that disrupt how your browser communicates with ChatGPT.
DNS or Network Redirects
DNS servers play a vital role in routing traffic. If you’re using a DNS server that is redirecting you improperly, or if your ISP uses internal redirects for blocked or unreachable domains, you might receive an error page in HTML format.
Cached HTML Responses
In some cases, your browser may have cached a failed or redirected HTML response from an earlier session. This cached content may be incorrectly served instead of a new, fresh response from the server.
Fix ChatGPT Login Error: “Unexpected Token ‘<‘, <!DOCTYPE… is Not Valid JSON”
Now that you understand the root cause, here are the solutions you can apply. These fixes work for both desktop and mobile users.
Switch from Mobile Data to Wi-Fi
Mobile networks are often the root of this issue due to how they handle traffic. Switching to a reliable Wi-Fi network usually clears the error immediately.
If you’re using a hotspot or mobile data plan, switch to your home or office Wi-Fi and reload ChatGPT. Avoid public Wi-Fi if possible, as these often have firewalls that interfere with secure data transmission.
Try a Different Internet Connection
Sometimes the issue lies with a specific Wi-Fi network. Switching to another network—such as a friend’s Wi-Fi or a different hotspot—can help. You may even consider connecting through a wired Ethernet cable if you’re on a PC or laptop for added stability.
Additionally, restarting your router can flush DNS settings and resolve temporary connectivity issues.
Disable or Enable VPN
If you are currently using a VPN, try disabling it. The VPN might be rerouting your traffic through servers incompatible with OpenAI’s login service.
Conversely, if you’re not using a VPN, enabling one may help you bypass network restrictions imposed by your ISP. In both cases, switching server regions within your VPN client can help improve compatibility.
Clear Browser Cache and Use Private Mode
Browsers often cache content—including failed login attempts or misrouted pages. If you’re seeing the same error repeatedly, it may be pulling the same broken HTML response from your cache.
Clear your browser’s cache, cookies, and local storage related to chat.openai.com. Alternatively, open ChatGPT in incognito or private mode for a fresh session with no cached files.
Try a Different Browser or Device
Occasionally, browser extensions or configurations can interfere with the login process. Switching to a different browser (like Firefox, Chrome, or Edge) or trying from another device (like a smartphone or tablet) can rule this out quickly.
If the Error Persists: Additional Steps and When to Seek Support
In rare cases, this issue may persist despite trying all the above methods. If so, consider the following:
- Wait and Retry Later: ChatGPT’s backend servers might be under heavy load or undergoing maintenance. Give it 15–30 minutes and try again.
- Check OpenAI Status Page: Visit status.openai.com to confirm there’s no active outage.
- Test on a New Device/Network: Logging in from another device or network can help confirm whether the issue is on your side or with the service.
- Contact OpenAI Support: If nothing works, submit a support request at help.openai.com, describing your issue and including a screenshot of the error.
Final Thoughts
The error message “Unexpected token ‘<‘, ‘<!DOCTYPE’… is not valid JSON” may sound alarming, but it’s one of the most common login-related issues users encounter on ChatGPT. It’s not a bug or a flaw in the app. It’s almost always related to how your device communicates over the internet.
Thankfully, it’s easily fixed by changing your network, tweaking VPN settings, or clearing your browser cache. By following the steps in this guide, you should be able to restore access to your ChatGPT account quickly and continue using the service without interruption.
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