Detect File Type - Local
Local-only, offline file type detection. Uses an embedded ML model (Google Magika) to identify 214 file types by content — no network calls, no API keys, no data leaves the machine. All inference runs on-device via ONNX Runtime.
When to Use
- Identify unknown files by their content (not just extension) — locally, without sending data anywhere
- Verify that a file's extension matches its actual content
- Check MIME types before processing uploads or downloads
- Triage files in a directory by type
- Detect extension mismatches and masquerading (e.g.,
.pdf.exe,.xlsx.lnk) - Flag suspicious polyglot-style payloads (for example PDF/ZIP or PDF/HTA-style chains)
- When privacy matters — file bytes never leave the local machine
Installation
pip install detect-file-type-local
From source:
pip install -e /path/to/detect-file-type-skill
Usage
Single file
detect_file_type path/to/file
Multiple files
detect_file_type file1.pdf file2.png file3.zip
Recursive directory scan
detect_file_type --recursive ./uploads/
From stdin
cat mystery_file | detect_file_type -
# Optional best-effort fast path (head only)
cat mystery_file | detect_file_type --stdin-mode head --stdin-max-bytes 1048576 -
Output formats
detect_file_type --json file.pdf # JSON (default)
detect_file_type --human file.pdf # Human-readable
detect_file_type --mime file.pdf # Bare MIME type
Programmatic (Python)
python -m detect_file_type path/to/file
Output Schema (JSON)
Single file returns an object; multiple files return an array.
{
"path": "document.pdf",
"label": "pdf",
"mime_type": "application/pdf",
"score": 0.99,
"group": "document",
"description": "PDF document",
"is_text": false
}
Fields
| Field | Type | Description |
|---|---|---|
path |
string | Input path (or - for stdin) |
label |
string | Detected file type label (e.g., pdf, png, python) |
mime_type |
string | MIME type (e.g., application/pdf) |
score |
float | Confidence score (0.0–1.0) |
group |
string | Category (e.g., document, image, code) |
description |
string | Human-readable description |
is_text |
bool | Whether the file is text-based |
Exit Codes
| Code | Meaning |
|---|---|
| 0 | All files detected successfully |
| 1 | Fatal error (no results produced) |
| 2 | Partial failure (some files failed, some succeeded) |
Error Handling
Errors are printed to stderr. Common cases:
- File not found:
error: path/to/file: No such file or directory - Permission denied:
error: path/to/file: Permission denied - Not a regular file:
error: path/to/dir: Not a regular file
When processing multiple files, detection continues for remaining files even if some fail.
Limitations
- Default stdin mode (
spool) writes stdin to a temporary file and uses Magika path detection. --stdin-mode headis best effort and may miss trailing-byte signatures.- Very small files (< ~16 bytes) may produce low-confidence results
- Empty files are detected as
empty - Detection is content-based — file extensions are ignored