How to use File Type Checker
- Choose the source files or enter the requested value.
- Review detected facts, settings, and safety limits before processing.
- Download or copy only the result you have reviewed.
File Type Checker
Identify a file type from bounded magic bytes, container evidence, browser MIME, and filename extension instead of trusting the name alone.
You can also drop files anywhere in this panel.
Private by design. Only a bounded prefix is normally read; bounded ZIP inspection is used for Office container subtypes.
Choose any file to inspect its prefix.
Compare a filename extension with evidence found inside the file rather than trusting its name alone.
How OpenFileTools processes it
Local processing, explicit choices.
OpenFileTools performs this workflow locally after an explicit action. File bytes, paths, passwords, and results are not uploaded, persisted, logged, or added to URLs.
Quick technical summary
What this tool changes.
| Property | Behavior |
|---|---|
| Processing | Browser only; no image upload |
| Original | Never changed |
| Evidence | Extension, browser MIME, magic bytes, bounded container structure |
| Typical direct read | Initial 4 KB |
| Malware scan | No |
Check the bytes, not only the filename
A filename extension can be changed easily, and a browser MIME value can be generic or inferred from that extension. This checker reads bounded signature evidence and compares it with the filename and MIME declaration so mismatches are visible.
- Direct signature checks normally use only the initial 4 KB.
- Office files receive bounded ZIP-package inspection for DOCX, XLSX, and PPTX evidence.
- Shared ISO media containers can remain container-level or subtype-level evidence depending on what is exposed.
Identification is evidence, not a security verdict
Recognizing a valid PDF, image, ZIP, Office document, or executable does not prove the file is safe. The tool does not execute the file, scan it for malware, or validate every byte in a large container.
- Unknown is preferable to inventing a type from weak evidence.
- Renaming a file extension does not convert the content.
- Unexpected executable or active document types deserve separate security review.
Questions, answered.
What are magic bytes?
They are characteristic byte sequences or structural markers near the beginning of many file formats.
Can a file have the wrong extension?
Yes. The tool reports the mismatch rather than trusting the filename.
Why can some results be ambiguous?
Some formats share containers or do not expose enough identifying evidence in a bounded read.
Is the file uploaded?
No. The bounded inspection stays in your browser.
Related guide
Read the related guide