Claude Attachments Not Uploading or Failing to Process? Here's the Fix

Step-by-Step Fix

1. Check the file before you upload

Before troubleshooting the browser or network, verify the file itself meets Claude's requirements:

• Size: Each file must be under 10 MB. Check your file size in Finder (Mac) or File Explorer (Windows) by right-clicking and choosing Properties/Get Info.
• Format: Stick to PDF, .docx, .txt, .md, .csv, PNG, JPG, GIF, WebP, or common code files. If you have an Excel or PowerPoint file, export it as PDF first.
• Integrity: Open the file locally to confirm it is not corrupted. A corrupted PDF, for example, will fail to process even if the file size is fine.

If the file passes those checks, move to the next step.

2. Run the two isolation tests

These two tests tell you immediately whether the problem is local or server-side:

Test A — Incognito window:

1. Open an incognito (Chrome) or private (Firefox/Safari/Edge) window.
2. Go to claude.ai and sign in.
3. Try uploading the same file.

Test B — Different network:

1. Enable your phone's mobile hotspot.
2. Connect your computer to it (turn off Wi-Fi and unplug Ethernet).
3. Retry the upload on your normal browser.

• If Test A works → your normal browser session/extensions are the issue (go to Step 3).
• If Test B works → your primary network/VPN is blocking the upload (go to Step 4).
• If both fail → likely a server-side issue or account problem (go to Step 5).

3. Clear browser session state

If incognito worked but your normal browser did not, your session data is stale:

1. In Chrome: go to Settings → Privacy and Security → Clear browsing data.
   • Check Cookies and other site data and Cached images and files.
   • In the Advanced tab, set the time range to All time.
   • Click Clear data.
2. In Firefox: go to Settings → Privacy & Security → Cookies and Site Data → Clear Data.
3. In Safari: go to Develop → Empty Caches, then Safari → Clear History.
4. Close all Claude tabs completely.
5. Reopen claude.ai and sign in fresh.
6. Retry the upload.

Disable extensions first before clearing data — do both at the same time:

• Go to your browser's extension manager and turn off ad blockers, privacy tools (uBlock Origin, Privacy Badger, Ghostery), and any cookie-management extensions.
• If the upload works with extensions off, re-enable them one at a time to find the culprit.

4. Disable VPN or proxy

If your primary network blocked uploads but your hotspot worked:

1. Disable your VPN client entirely (not just pause — disconnect and quit).
2. If you use a corporate or school network with a proxy, test on a personal network instead.
3. Check your DNS settings — some DNS providers (NextDNS, Pi-hole) block content-delivery endpoints. Switch to 1.1.1.1 or 8.8.8.8 temporarily to test.
4. Retry the upload on your main network with VPN off.

5. Check for a service incident

If the problem appears on all networks and all browsers:

1. Visit status.anthropic.com and look for any active incidents affecting uploads or file processing.
2. If an incident is posted, wait for it to resolve — no local fix will help.
3. If no incident is listed, move to escalation.

6. Try alternative input methods

While troubleshooting, you can work around the upload issue:

• Paste text directly: Copy the document content and paste it into the Claude message box. This bypasses the upload pipeline entirely.
• Use a different file format: Convert your file to plain .txt or a simple PDF and retry.
• Try the Claude iOS or Android app: Mobile apps use a different upload path and sometimes succeed when the web app is having issues.

7. Escalate with a full report

If nothing above has worked, contact Anthropic support with the following details:

• Exact error message (screenshot it)
• File type and size
• OS name and version
• Browser name and version
• Time and timezone of the failure
• Whether you already tried incognito and a different network

Go to support.anthropic.com and open a ticket. The more detail you include, the faster support can identify whether this is an account-specific issue or a broader bug.

Why This Happens

Claude's file upload pipeline sends your attachment as a multipart HTTP request to Anthropic's servers, where it is parsed and converted into tokens before the model sees it. This process can fail at three points: (1) the browser fails to send the file — caused by extensions intercepting requests, stale auth cookies, or network blocks; (2) the file reaches the server but fails validation — caused by size over 10 MB, unsupported format, or a corrupted file; or (3) the server-side processing times out or errors — caused by platform incidents or very large files that push processing time limits. Most user-facing failures happen at point one, which is why clearing session data and disabling extensions resolves the majority of cases.

Common Mistakes to Avoid

• Retrying the upload repeatedly without changing anything. If the first attempt failed, the second attempt on the same session will fail the same way. Change something — incognito, different network, different browser — before retrying.
• Assuming the file format is supported without checking. Many users try to upload .xlsx, .pptx, or .mp4 files and assume any failure is a bug. Convert to PDF or text first.
• Forgetting to disable VPN before testing incognito. Incognito clears browser state but does not bypass your VPN. Test incognito AND switch networks as separate steps.
• Clearing cookies but keeping extensions active. Ad blockers can re-block requests even after a clean session. Disable extensions at the same time you clear cookies.
• Not checking status.anthropic.com first. During platform incidents, no local fix will work. Check the status page before spending time on browser troubleshooting.
• Uploading multiple large files at once when one is causing issues. Isolate to a single small test file to confirm the upload path works, then add files back one at a time.

File Format Conversion Quick Reference

If your file type is not supported, convert it before uploading:

| Original Format | Best Conversion | How to Convert | |-----------------|-----------------|----------------| | Excel (.xlsx) | PDF or CSV | File → Export in Excel/Google Sheets | | PowerPoint (.pptx) | PDF | File → Export → PDF in PowerPoint | | Word (.docx) | PDF or .txt | File → Export, or paste content directly | | Audio (.mp3, .m4a) | Transcript text | Use a transcription tool first | | Video (.mp4) | Transcript or notes | Extract the relevant text | | ZIP/RAR archives | Extract first | Upload individual files from inside the archive | | Large PDFs | Split into parts | Use a PDF splitter to keep each part under 10 MB |

Preventing Future Upload Failures

• Keep documents under 8 MB proactively — staying below the 10 MB hard limit gives you buffer for metadata overhead.
• If you regularly work with large documents, consider splitting them into logical sections (chapters, topics) that you upload separately.
• Maintain clean browser sessions by signing out of Claude when done for the day; stale cookies are a recurring cause of silent upload failures.
• On corporate or school networks, check with your IT team whether outbound multipart HTTP requests to anthropic.com are permitted — some content filters block file upload traffic.

Related Issues

• Claude attachments stuck processing
• Claude network error / request failed
• Claude request too large
• Claude attachment count limit reached
• Claude errors & bugs hub

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