About File Extension Info
File Extension Info looks up what a file extension stands for and returns a short plain-English description. Type pdf, docx or mp3, and it tells you what kind of file that extension names - the fastest way to settle what an unfamiliar suffix in a file name actually means.
The lookup is forgiving about how you type. The input is trimmed of surrounding whitespace, lowercased, and any leading dot is stripped, so PDF, .pdf and pdf all resolve to the same entry. A known extension returns a line of the form .ext: Description, such as .pdf: Portable Document Format (Adobe), while anything outside the list returns a no-info message instead.
The scope is a fixed dictionary of about thirty-five common extensions - documents, images, archives, audio and video - rather than a full registry. It maps an extension to a description only: it does not read the file, does not detect a type from its bytes, and does not show a MIME type or a default application. For a suffix outside the list, or an empty input, the tool reports No info rather than guessing.
How to use File Extension Info
- 1 Type or paste the file extension you want to look up.
- 2 Read the description, which is returned with the leading dot restored.
- 3 Enter it without the dot if you prefer - the tool strips a leading dot on its own.
Frequently asked questions
How should I type the extension?
Any common form works. The input is trimmed, lowercased and has a leading dot stripped, so pdf, PDF and .pdf all resolve to the same entry.
Does it read my file to detect the type?
No. It only maps an extension string to a short description. It does not open a file, does not inspect its bytes, and cannot tell apart two files that merely share the same extension.
Why did I get a no-info message?
The dictionary holds about thirty-five common extensions, so anything outside that set returns No info. An empty input does the same, reporting No info for "." rather than prompting for a value.
Does it show the MIME type?
No. Only a short plain-English description is shown, with no MIME type, vendor or default application. For MIME types specifically there is a separate reference tool.
Free, online, and private
Free to use
File Extension Info is completely free. There is no account to create, no login, and no hidden charge or usage limit.
Runs online in your browser
It is a free online tool that runs entirely in your browser. Nothing to download or install — open the page and start using it right away.
Your data stays private
All processing happens locally on your device. Your input is never uploaded, stored, or tracked, so it never leaves your browser.
How File Extension Info behaves in detail
These are the specifics of this implementation — the exact ranges, defaults and fixed settings you are working with.
| Parameter | Value |
|---|---|
| Input | one text panel, recalculated live on every keystroke; the sample reads pdf |
| Normalisation | the input is trimmed, lowercased and has any leading dot stripped before the lookup |
| Output | a known extension returns a line of the form .ext: Description, and an unknown one returns No info for ".ext" |
| Coverage | about thirty-five common extensions, from documents and images to archives, audio and video |
| Sample | pdf reads .pdf: Portable Document Format (Adobe) |
| Case | PDF and pdf resolve to the same entry because the input is lowercased first |
Compiled from the implementation of this tool and checked against it by itoolnet.
What File Extension Info does not do
Knowing the edges of a tool saves more time than another list of its features. These are the cases where it will not do what you might expect.
- The dictionary is a fixed set of about thirty-five entries, not a full registry. No MIME type, no vendor, no default application and no category are shown, and any extension outside the list returns the generic no-info message.
- The lookup only maps an extension to a short description. It does not read a file, does not detect a type from bytes, and cannot distinguish two files that merely share the same extension.
- An empty or blank input produces No info for "." with no prompt, and there is no search or browse mode - you must know the extension you want to look up and type it in full.
Tested and documented by itoolnet, the team that builds and maintains this site.