Your files stay on your device

# File upload security policy builder

Describe your upload rules and get a policy document plus server-side enforcement snippets for Nginx, Express, or ASP.NET Core.

Describe the uploads, the allowlist, and a size cap to build the policy.

The principle behind every line: only server-side checks are security controls. The extension on a filename is a claim, the stored bytes are the evidence; that is why the snippets read the file header against a signature table instead of trusting the MIME header. Honest limits of this builder: it writes templates, not reviewed code; its signature table covers common families (PNG, JPEG, GIF, WebP, PDF, ZIP-based office files, MP4, and more) and names any extension it cannot check rather than inventing one; and it cannot scan files or re-encode them here. Those steps exist as hooks in the code for your server to run.
Options

## More config file tools

- [nginx.conf explainer](/config/nginx)
- [SSH config explainer](/config/ssh)
- [Password policy tester](/crypto/password-policy-tester)
[All config file tools](/config)

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Canonical HTML: https://nutter.tools/config/file-upload-security-policy-builder
Markdown version: https://nutter.tools/config/file-upload-security-policy-builder.md
Plain-text version: https://nutter.tools/config/file-upload-security-policy-builder.txt
Agent index: https://nutter.tools/llms.txt