About File-Extension.com

File-Extension.com is an independent, ad-supported publisher of practical guides on how to open, identify and safely handle file extensions — from everyday ones like .zip and .pdf to obscure or ambiguous ones like .dat and .tmp.

What makes this site different

Most "how to open a .xyz file" pages online are thin rewrites of each other. We take a different approach: many of our guides include a free client-side tool that reads supported parts of the file in your browser. Other guides explain native opening, export or authorized access — with scope and limitations described on the relevant guide.

Concretely, that means our tools implement real parsers against the actual public specifications and reverse-engineered documentation for each format — the PE/COFF header layout for .dll files, the ZIP central directory for .zip/.xlsx/.apk, the OpenPGP packet format for .sig files, and so on. Where a format has no public specification at all (like .dwg), we say so plainly instead of pretending to parse something we can't — see, for example, our .dwg guide, which deliberately limits itself to what can be verified from the file's own version signature.

Every tool runs entirely in your browser. Nothing you open is uploaded to a server — we architected it this way specifically so you can safely inspect files you don't fully trust yet.

How these guides and tools work

We use format specifications, vendor documentation and open-source references to explain how to open files. A browser inspector can identify or extract supported structures; it is not always a replacement for the original application.

Tools process selected files locally in the browser. The site combines custom format readers with open-source libraries, including JSZip for ZIP-based packages, PDF.js for PDF viewing, libarchive for archive extraction, and Pyodide for browser-based Python. No single implementation supports every possible file or device.

Limits are described beside the tools and in the guides: unsupported encodings, missing companion files, encryption, browser decoding and memory limits can prevent a result. Identifying a signature or an end marker does not certify that a file is safe or intact.

When checking a result, compare it with the original app or a reference implementation. We do not claim that this downloadable site package includes an automated test suite for every tool. Tell us about an incorrect result using the contact address below.

How this site is funded

File-Extension.com is supported by advertising (Google AdSense). We don't accept payment to recommend a specific third-party program, and our tools favor showing you what's inside a file for free over pushing paid software. See our Privacy Policy for details on how ads and analytics work on this site.

Contact

Found an inaccuracy, a bug in one of the tools, or have a file extension you'd like us to cover? We'd like to hear about it: contact@file-extension.com.