catalog / environment

/mnt/user-data/uploads/ is read-only on Claude.ai

verified

/mnt/user-data/uploads/ on Claude.ai is read-only — skills that try to write there for round-tripping uploaded files fail with a permission error. Use /mnt/user-data/outputs/.

  • Category: environment
  • Applies to: Claude.ai ✅ | Claude Code ❌ (path doesn't exist) | Claude Desktop ❌
  • Verified on: Claude.ai web, 2026-05-17
  • Verification tier: verified
  • Severity: Hard error

Symptom

A SKILL.md that edits uploaded files in place on Claude.ai errors with a read-only filesystem error.

Cause

/mnt/user-data/uploads/ is mounted read-only. Skills cannot modify uploaded files in place.

Reproduction

Reproduced 2026-05-17 on Claude.ai web: echo > /mnt/user-data/uploads/x.txt → Read-only file system.

Fix

Copy uploaded files to a writable location (/home/claude/ in the Claude.ai sandbox) before modifying.

Notes

This path doesn't exist on Code or Desktop, so the pitfall is Claude.ai-only — but a SKILL.md authored on Claude.ai and ported elsewhere will reference a path that no longer resolves.