File Extension Checker Online
Check a file's extension, detected category, MIME type and size instantly with ZeroKB's free File Extension Checker. Files are checked in your browser and are not uploaded for this check.
Your selected file's details will appear below.
File Information
What Is a File Extension?
A file extension is the part of a filename that usually appears after the final dot. It helps people and software recognize the kind of file they are working with. Examples include .pdf for PDF documents, .jpg and .png for images, .docx for Word documents, .xlsx for spreadsheets, .mp4 for video and .zip for compressed archives. An extension is a useful clue, but it does not by itself guarantee that a file's contents match the name.
How to Check a File Extension Online
Using the ZeroKB File Extension Checker is simple. Select Browse Files or drag a file into the upload area. The tool reads basic information provided by your browser and displays the filename, extension, file category, MIME type and size. No account or software installation is needed. When you want to check another file, select it in the same upload area; the details update to show the newly selected file.
Step 1: Choose a File
Pick a file from your computer, tablet or phone. The checker accepts files through your device's standard file picker, so you can inspect many common formats.
Step 2: Review the Details
Check the extension and category shown in the results. If your browser provides a MIME type, it will also be displayed. File size is shown in a readable unit such as Bytes, KB, MB or GB.
Step 3: Use the Information Carefully
Use these details to help organize files or decide which application may open them. If a file looks suspicious or its extension seems misleading, do not open it simply because the checker displays a familiar type.
What Is a MIME Type?
A MIME type is a technical label used by browsers and applications to describe a file's media format. Examples include image/jpeg, image/png, application/pdf and text/plain. A browser may not provide a MIME type for every file, so the result can say “Not available.” The MIME type shown by this tool comes from the browser's file information; it is not a deep security scan or a guarantee of the file's true contents.
Common File Extensions and Their Uses
PDF files are often used for documents intended to look consistent across devices. JPG, PNG, WEBP and GIF are common image formats. DOC and DOCX are associated with word-processing documents, while XLS and XLSX are spreadsheet formats. PPT and PPTX are presentation formats. ZIP, RAR and 7Z are archive formats; MP3 and WAV are audio formats; MP4, MOV and WEBM are video formats. Some file types can use different extensions, and a single extension may be associated with more than one application.
Does the File Extension Prove a File Is Safe?
No. A filename extension is easy to change, and a file can be renamed to look like another format. This checker reports basic file details; it does not scan for malware, verify a digital signature or inspect every part of the file. Be cautious with unexpected attachments, double extensions and files from unknown senders. Keep your operating system and security software updated, and only open files from sources you trust.
Privacy and Browser-Based Checking
The checker uses the file selected in your browser to read its name, size, extension and browser-reported MIME type. This page's checker does not need to send the file to a ZeroKB server for these details. As always, avoid selecting sensitive files on a device or browser you do not trust, and remember that browser extensions or other software installed on your device may have their own permissions.
Explore More Free ZeroKB Tools
Once you know the file format, you can choose a tool for the next task. Use the File Size Converter to understand or convert KB, MB and GB values. Reduce an image with the Image Compressor, or make a PDF smaller with Compress PDF. If you need to turn pictures into a document, try Images to PDF. These related utilities help with common file tasks directly from your browser.
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Frequently Asked Questions
What is a file extension?
A file extension is the suffix after the final dot in a filename, such as .pdf, .jpg or .docx. It commonly indicates the format associated with the file.
How do I check a file extension online?
Select a file in the upload area. The checker displays its filename, extension, detected category, browser-reported MIME type and size.
Can I check different types of files?
Yes. You can select many file types. The category is identified from a list of common extensions and, when available, the MIME type reported by the browser. Some uncommon formats may appear as “Unknown / Other.”
What does “No Extension” mean?
It means the selected filename has no dot followed by an extension, or the dot is the first character in the name. The checker uses the filename rather than opening or analyzing the file's contents.
What is a MIME type?
A MIME type is a technical label such as image/jpeg or application/pdf that helps software identify a media format. It may be unavailable for some files.
Does this tool show file size?
Yes. It displays the selected file's size in Bytes, KB, MB, GB or TB as appropriate.
Are my files uploaded to ZeroKB?
This checker reads basic file properties in your browser and does not need to upload the selected file to a ZeroKB server. It does not perform a malware scan.
Can this tool tell me if a file is safe?
No. File extensions and MIME types can be misleading and are not a security verdict. Only open files from trusted sources and use appropriate security software.