File Extension Lookup

Look up common file extensions, MIME types and descriptions. The tool runs in your browser and is designed for quick developer workflows without sending input to a server.

Extension or MIME

Output

.json — application/json — JSON data

Runs fully in your browser. Input is not sent to a server, logged, stored, or transmitted.

How to use this tool

Enter the required values in the labeled fields. Results update in your browser and are announced for assistive technologies. Use realistic measurements and verify important outcomes before acting on them.

Formula or logic

Input is processed locally in the browser. The tool does not execute remote requests, call backend APIs, store pasted data, or transmit secrets.

Example calculation

Example: paste input, choose options, and copy the generated output.

Practical use and limits

This page is built for small developer workflow checks that should not require an account, API call or pasted data upload. The calculation is intentionally visible and described above so you can sanity-check the result instead of treating it as a black box.

Limit: the output is a helper for inspection and formatting, not a security audit or production validation guarantee. For important decisions, use this result as a planning aid and verify it against the relevant source of truth.

Last reviewed: May 29, 2026.

File Extension Lookup: practical guide

File extensions are small clues, not guarantees. They help identify likely format, app association and risk, but the real file content can still differ.

Use lookup as a first pass before opening unknown files, cleaning uploads or explaining file types to non-technical users.

Real examples

Archive file

Input: .zip

Result: compressed archive, inspect before extracting

Data file

Input: .csv

Result: comma-separated values, often spreadsheet-compatible

Practical notes

Extensions can be renamed or spoofed.
MIME type and file signature are stronger signals.
Unknown executable extensions deserve extra caution.

Common mistakes

Trusting extension alone for security.
Opening unknown attachments casually.
Confusing similar extensions from different ecosystems.

Frequently asked questions

Is my input sent to a server?

No. This developer tool runs fully in your browser and does not upload, log, store, or transmit pasted data.

Does this execute code or network requests?

No. It only transforms, formats, validates, or generates text locally unless the page explicitly says otherwise.

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