Accurate MIME Type Checker Online

MIME Type Checker

What a MIME type is

A MIME type is a label that tells software what kind of data a file contains. A browser may report image/jpeg for a photo, application/pdf for a document or text/html for a web page. The label is written as a type and a subtype, separated by a slash. Software uses these labels to choose an icon, a preview handler or an application. The MIME type is not the same thing as the file extension, even though the two often match in everyday use.

What this checker shows

This page reads one file that you choose and displays the browser-reported MIME type, the file name, the size and the last-modified date. It also shows a short description for common types and a file icon. Everything happens in the browser, so the file is not uploaded. The result is a quick inspection of what the browser believes the file is. It is useful for debugging an upload, checking a download or understanding why a file opens in an unexpected application.

How the browser decides the type

Browsers usually derive the type from the file extension and the operating system's file association table. Some browsers add a guess based on the content for a few formats, but that behaviour is not consistent. A file named photo.jpg will normally be reported as image/jpeg even if its bytes are something else. A file with no extension may come back as an empty type or application/octet-stream. This is why the result describes the browser's view, not a forensic examination of the file.

How to check a file

Press the choose-file button, select one file and wait for the details panel. Read the MIME type first, then check the size and date. If you are preparing an upload, compare the reported type with the list of accepted types on the destination site. If the site expects image/png and your file reports image/jpeg, converting the image is safer than renaming it. Use the clear or choose-another control to test a second file.

Reading the result

A value such as image/png is a good sign that the browser associates the file with PNG. A value such as application/octet-stream usually means the browser does not know the format. An empty value can happen when the file has no extension or the operating system has no association. None of these results proves that the file is safe. A malicious file can be given a harmless extension, and a valid image can contain hidden data. Treat the label as a hint, not a security certificate.

Common MIME types

Why a MIME type can be wrong

A file extension is easy to change. Renaming report.exe to report.jpg does not turn it into an image, but some browsers will still report image/jpeg because they trust the name. Server-side validation should read the file signature, inspect the decoded contents and enforce an allow-list. This client-side checker does not read magic bytes, does not scan for malware and does not verify that the internal structure matches the label. That limitation matters when you are building an upload form or checking an untrusted download.

When this checker is useful

Use it to confirm why a file is rejected by a website, to see whether a download has an unexpected association, or to explain the difference between an extension and a media type to a colleague. It is also handy when preparing assets for a CMS that lists accepted MIME types. For a quick check on a personal computer, it is faster than opening a terminal. For a production upload pipeline, it is only the first, weakest layer of validation.

Privacy and local processing

The selected file is read by the browser so that it can show the name, size and date. The tool does not send the file to Newisty and does not store it. Your browser and operating system still see the file, and any preview or download you open is handled by your own software. Avoid testing confidential documents on a shared computer, and remember that clearing the page does not remove the original file from your disk.

Common problems

If the choose-file dialog will not open, try clicking the visible button rather than the label. If the type is blank, add the correct extension and test again, but do not assume the content is now valid. If the browser reports a generic type for a file that opens normally, the operating system may simply lack an association. If the size looks wrong, check whether the file is still downloading or whether you selected a shortcut rather than the file itself.

What not to do

Do not use this page as a malware scanner. Do not conclude that a file is safe because it reports image/png. Do not rename a file to bypass a server's upload rules. Do not rely on the browser's MIME guess for access control, billing or legal evidence. Do not upload a confidential file to a third-party checker when a local inspection is enough. The right place for strict validation is the server that receives the file, using content inspection and an allow-list.

A practical validation checklist

For a website upload, check the extension, the declared MIME type, the file signature and the decoded structure. Enforce a maximum size, generate a new file name, store files outside the web root and serve them with a safe Content-Type. If images are allowed, re-encode them rather than serving the original bytes. Log rejections and rate-limit repeated attempts. This checker can help you debug the first two steps, but it cannot replace the rest of that checklist.

Frequently Asked Questions