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NeatUtility

MIME Type & File Extension Lookup

Web & API100% Client-Side
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About this tool, examples & FAQ

Lookup standard IANA media types and file extensions instantly in your browser with zero remote requests. Resolve Content-Type headers, detect binary vs text encodings, filter by media category, and export structured JSON MIME dictionaries.

Key facts

Verified capabilities and limits of this utility
Registry AuthorityIANA Media Types Registry (RFC 2046, RFC 6838)
Media CategoriesApplication, Text, Image, Audio, Video, and Font
Maximum Input25 KB
Execution Deadline2 s

How to use

  1. Enter a file extension (e.g. `png`, `.json`, `wasm`) or full MIME type (e.g. `application/pdf`).
  2. Select your desired view: Detailed Lookup, Structured JSON, or Browse Category.
  3. Optionally filter by top-level category (Image, Font, Application, Text) or toggle compact mode.
  4. Click Run (or press Ctrl/Cmd + Enter) to immediately inspect media definitions and HTTP headers.
  5. Copy the verified MIME type string or Content-Type header directly into your web server config.

Example

Lookup standard PNG image MIME type and Content-Type header

Input

png

Example output

=== MIME Type & Extension Lookup (1 found) ===

MIME Type:     image/png
Extensions:    .png
Category:      image
Format Type:   Binary
Description:   Portable Network Graphics lossless compressed bitmap (W3C standard)
HTTP Header:   Content-Type: image/png

Edge cases

JavaScript MIME Type Standardization

RFC 9239 officially obsoleted historic types like `text/javascript` and `application/x-javascript` in favor of standard `text/javascript` for HTML script elements and `application/javascript` in traditional registries.

Charset Directives for Text Types

Text MIME types (`text/html`, `text/css`, `text/plain`) should include `charset=utf-8` in their HTTP Content-Type headers to prevent legacy character encoding vulnerabilities.

Dot Prefix Tolerance

The lookup engine seamlessly resolves queries whether entered with a leading dot (`.webp`) or bare extension (`webp`).

How it works

  1. Matches queries against a comprehensive client-side dictionary of standard IANA media types.
  2. Resolves bidirectional mappings between file extensions and media type strings.
  3. Provides pre-formatted HTTP Content-Type headers with canonical character set parameters.
  4. Operates entirely offline inside Web Worker threads without tracking or outbound requests.

Related workflows

Frequently asked questions

What is a MIME type (Media Type)?

A MIME (Multipurpose Internet Mail Extensions) type is a standardized two-part identifier (e.g. image/webp) transmitted in HTTP headers to inform browsers and clients how to interpret and render a file's byte stream.

Why is the correct Content-Type header critical for web performance?

If a web server serves files with incorrect Content-Types (such as serving WebAssembly as application/octet-stream or JavaScript as text/plain), modern browsers will refuse execution or fail streaming compilation due to strict MIME type sniffing protections.

What does application/octet-stream signify?

application/octet-stream is the universal binary fallback MIME type indicating arbitrary binary data. Browsers typically prompt a file download rather than attempting inline rendering.

References