The Filesystem MCP server only performs local file I/O. It has the simplest policy.
What it needs
| Resource | Access | Details |
|---|
| Filesystem | Read | Only the directories it should serve |
| Network | None | No internet access |
| Env | None | No variables |
Complete Policy
command: ["node", "@modelcontextprotocol/server-filesystem"]
filesystem:
read:
- "./my-files" # Only this directory is served
write: [] # Write nothing (read-only)
network:
allow: [] # No network
env:
allow: [] # No env vars
limits:
memory_mb: 128
timeout_s: 60
How to run
# Step 1: Install the server
npm install -g @modelcontextprotocol/server-filesystem
# Step 2: Run sandboxed
warden run --policy policy-filesystem.yaml
Tips
- Grant only the directories you actually need
- Use
write: [] if you only need to read
- If it needs write access, give it a separate directory (the output dir)
- This is the most secure server, no network, no env
Variations
Read + Write access
filesystem:
read:
- "./data"
write:
- "./output" # Output files go here
Multiple directories
filesystem:
read:
- "./documents"
- "./images"
- "./config"
write: []
Troubleshooting
| Error | Fix |
|---|
permission denied | Check that the directory is listed in filesystem.read |
| File not found | The path is relative to the policy file's folder |
| Write failed | Add the directory to filesystem.write |
Resources
