A Claude upload can fail before transfer, after transfer, or during document analysis. Test a small text file first. If that succeeds, the account and browser can upload files, so the original document needs inspection.

Anthropic can change supported formats, file sizes, page handling, and plan allowances. Check the official guide for the current limits.

Separate the Failure Stage#

What happensCheck first
File is rejected immediatelyType, size, account feature, and browser
Upload stops or reports a network issueService status, browser, VPN, proxy, and file copy
Upload completes but analysis failsPage count, token length, corruption, encryption, or content
Spreadsheet cannot be attachedSupported type and code execution or file creation setting
Images inside a document are ignoredDocument type and Claude’s visual-processing rules

Create a Controlled Test#

  1. Start a new Claude chat.
  2. Create a small .txt file containing one sentence.
  3. Upload it.
  4. Ask Claude to repeat the sentence.

If the test fails, move to the browser and account checks. If it works, save a fresh copy of the original file and continue below.

Repair the Original File#

Open the file in its normal application and confirm that it is readable.

  • Save a new copy with a short filename.
  • Remove password protection only when authorized.
  • Export cloud-native documents to PDF or DOCX.
  • Split large documents by chapter.
  • Flatten complex PDFs only when searchable text is preserved.
  • Remove corrupted embedded media.
  • For spreadsheets, remove unused sheets, empty formatted rows, and oversized images.

For a PDF, use the page numbers shown by the PDF viewer when asking Claude about a page. Printed page labels inside the document may differ.

Check PDF Visual Analysis#

Claude can handle text and visual elements differently depending on the model, file length, and current product rules. If charts or images are important:

  1. Open the PDF and confirm the chart is sharp.
  2. Keep the relevant section within the official page guidance.
  3. Upload the relevant pages as a smaller PDF when possible.
  4. Ask Claude to describe the chart before asking for a conclusion.
  5. Compare the description with the source.

For non-PDF documents, embedded images may not be interpreted like PDF visuals. Export the relevant page to PDF or upload the source image separately.

Check Account Features and Settings#

Some file types can depend on features such as code execution and file creation. If an XLSX or similar file cannot be attached:

  1. Open Claude settings.
  2. Confirm that the required analysis feature is enabled.
  3. Start a new chat.
  4. Upload a small spreadsheet.
  5. Ask for one cell value.

For an organization account, the workspace administrator may control features.

Rule Out a Browser or Network Conflict#

  1. Check Anthropic’s status page.
  2. Refresh Claude.
  3. Try a private window.
  4. Disable privacy extensions, script blockers, and download managers.
  5. Turn off VPN or proxy software for one test.
  6. Try another supported browser.
  7. Try another network.

If only one browser fails, clear site data for Claude or re-enable extensions one at a time.

Reduce Analysis Load#

A file can be within the byte limit but still contain too much extracted text for the current conversation.

  • Upload fewer files.
  • Start a fresh chat.
  • Split the document by task.
  • Remove appendices that are not needed.
  • Ask a specific question about one section.
  • Summarize each section separately, then combine the verified summaries.

Do not ask Claude to “read everything” when you need one table or clause. Name the section and the output you need.

Verify the Fix#

  1. Upload the small test file.
  2. Upload the repaired original file.
  3. Ask Claude to identify a known heading, page, or cell.
  4. Ask one narrow question with a manually verifiable answer.
  5. Repeat in a new chat if the current conversation is unusually large.

The upload is fixed when the file attaches, Claude can retrieve a known detail, and the answer matches the source. If it still fails, contact Anthropic Support with the timestamp, account type, browser, operating system, file type, approximate size, and a sanitized screenshot.