File Extension Lookup
Lookup file extension details — find the full format name, MIME type, associated programs, and category for any file extension.
File Extension Lookup
What is a file extension lookup?
A file extension is the suffix at the end of a filename, separated from the name by a dot — for example the .pdf in report.pdf. Operating systems and applications use that suffix as a hint about what kind of data the file contains and which program should open it. A file extension lookup tool lets you type an extension and instantly see its full format name, description, MIME type, category, and the programs that can open it.
This is useful whenever you receive a file you do not recognise. Instead of guessing or risk opening something in the wrong application, you can look up what the extension actually means. It is also handy for developers building upload validators, designing icons for file lists, or documenting accepted formats.
This tool searches a built-in database of more than one hundred common file extensions covering documents, images, audio, video, archives, web files, source code, fonts, CAD, 3D models, and system files. Matching happens live in your browser as you type, so results appear immediately without any page reload or server round trip.
Key Information a Lookup Provides
- Format name — the full, human-readable name of the file format, such as "Portable Document Format".
- Description — a short explanation of what the format is used for and how it behaves.
- MIME type — the standard media type identifier browsers and servers use, for example
application/pdf. - Category — a grouping such as Image, Audio, Video, Document, Archive, Data, Web, or System.
- Compatible programs — a list of common applications that can open the file.
- Related matches — variants and similar extensions shown together so you can compare them.
- Type an extension — Start typing any file extension, with or without the leading dot. Results update live as you type.
- View the details — See the format name, description, MIME type, category, and compatible programs for each match.
- Browse multiple matches — If several extensions match, all are listed so you can compare the variants side by side.
- Refine your search — Keep typing to narrow the list, then clear the field with the Clear button to start again.
Common File Extensions Reference
| Extension | Category | MIME Type |
|---|---|---|
| .txt | Text | text/plain |
| .html | Web | text/html |
| Document | application/pdf | |
| .docx | Document | application/vnd.openxmlformats-officedocument.wordprocessingml.document |
| .jpg | Image | image/jpeg |
| .png | Image | image/png |
| .mp3 | Audio | audio/mpeg |
| .mp4 | Video | video/mp4 |
| .zip | Archive | application/zip |
| .json | Data | application/json |
| .woff2 | Font | font/woff2 |
| .exe | System | application/x-msdownload |
Worked Examples
- Looking up .pdf — Shows "Portable Document Format", MIME
application/pdf, category Document, and readers such as Adobe Acrobat, Chrome, and Preview. - Looking up .jpg — Shows "JPEG Image", MIME
image/jpeg, category Image, and editors such as Photoshop, GIMP, and Preview. - Partial match with jp — Typing "jp" surfaces both .jpg and .jpeg so you can compare the two JPEG variants at once.
- Looking up .woff2 — Shows "Web Open Font Format 2", MIME
font/woff2, category Font, and modern browser support. - Typing with the dot — Entering ".svg" works exactly the same as entering "svg", because the leading dot is stripped automatically.
Tips and Common Mistakes
- Extensions are not proof of content — A file can be renamed to any extension. To be certain of a format, check the actual file signature or "magic bytes" rather than trusting the name alone.
- Case does not matter here — The lookup lowercases your input, so ".PDF" and ".pdf" return the same result.
- No dot required — Type the extension with or without the leading dot; both forms are handled automatically.
- Partial typing works — You do not need the full extension. Typing the first few letters lists every match that starts with them.
- Not every extension is listed — The database covers the most common formats. Very rare or proprietary extensions may not appear.
- MIME types can vary — Some formats have several accepted MIME types, and servers may report the generic
application/octet-streamwhen the type is unknown.
Common Use Cases
A quick extension lookup answers a surprising number of everyday questions. Here are some of the most common situations where it helps:
- Identifying an unknown file — When you receive a file with an unfamiliar suffix, look it up to confirm the format and which application opens it.
- Choosing the right program — See a list of compatible applications before deciding what to install or open.
- Building upload validators — Developers can confirm the correct MIME type to check against when accepting or rejecting file uploads.
- Documenting accepted formats — Reference the exact MIME types and names when writing help pages or API documentation.
- Understanding file categories — Group extensions by category — image, audio, archive and so on — when organising assets or building file managers.
- Verifying safety — Recognising that an unexpected executable such as .exe or .bat deserves caution before it is opened.
How many file extensions are in the database?
The database currently includes 100+ of the most common file extensions across all categories — documents, images, audio, video, archives, web development, programming, 3D, CAD, fonts, and more.
What is a MIME type?
A MIME type (Multipurpose Internet Mail Extensions) is a standard identifier used by browsers and applications to indicate the type of data contained in a file. For example, text/html for HTML files.
Can I look up extensions without the dot?
Yes. You can type "pdf" or ".pdf" — the lookup handles both formats automatically.
Does a file extension guarantee the file contents?
No. An extension is only a name-based hint. A file can be renamed to any extension, so it may not match its real contents. For certainty, inspect the file signature or magic bytes.
Is the lookup case-sensitive?
No. Your input is converted to lowercase before matching, so ".PDF", ".Pdf", and ".pdf" all return the same results.
Can I search by typing only part of an extension?
Yes. The lookup matches exact extensions, extensions that start with your text, and extensions your text starts with. Typing "do" lists .doc and .docx among others.
Why is my extension not found?
The database focuses on the most common formats. Very rare, proprietary, or newly created extensions may be missing, in which case the tool reports that no results were found.
Does looking up an extension open or upload my file?
No. This tool looks up the extension only and runs entirely in your browser. You never upload a file, and no data leaves your device.