MIME Types

MIME (Multipurpose Internet Mail Extensions) types tell the client (browser) what kind of content is being sent, so the client knows how to handle or render it.

Format: type/subtype

Examples

MIME Type	Meaning
text/html	HTML page
text/css	CSS
application/javascript	JavaScript
image/png	PNG image
application/pdf	PDF file

Why MIME Types Matter in NGINX

Correct MIME types ensure:

• Proper rendering in browsers
• Correct file downloads
• Security (avoid content sniffing)
• Compatibility with clients and APIs

Wrong MIME types can cause:

• ❌ Files downloading instead of rendering
• ❌ Broken web pages
• ❌ Security warnings

How NGINX Determines MIME Types

NGINX determines the Content-Type header using this order:

1. Explicit types mapping
2. Included mime.types file
3. default_type fallback

Core Directives for MIME Types

Directive	Context	Purpose
types	http, server, location	Map extensions → MIME types
include mime.types	http	Load standard mappings
default_type	http, server, location	Fallback MIME type

Standard MIME Configuration (Recommended)

http {
    include mime.types;
    default_type application/octet-stream;
}

• mime.types contains hundreds of standard mappings
• application/octet-stream forces download for unknown files

The mime.types File Explained

Typical Location

/etc/nginx/mime.types

Example Content

types {
    text/html html;
    text/css css;
    application/javascript js;
    image/jpeg jpg jpeg;
    image/png png;
    application/json json;
}

• Multiple extensions can map to one MIME type
• NGINX matches by file extension

MIME Type Resolution Example

Config

root /var/www/html;

Files

/var/www/html/
├── index.html
├── style.css
├── app.js
├── logo.png
├── data.json

Client Receives

File	Content-Type
index.html	text/html
style.css	text/css
app.js	application/javascript
logo.png	image/png
data.json	application/json

default_type Directive

Syntax

default_type mime-type;

Example

default_type text/plain;

• Used when no MIME match exists
• Overrides default behavior if defined in lower context

Overriding MIME Types (Custom Mapping)

Example: Force .log Files to Download

types {
    text/plain log;
}

Example: Force File Download

location /downloads/ {
    default_type application/octet-stream;
}

MIME Types Per Location

location /media/ {
    types {
        video/mp4 mp4;
    }
}

• Overrides MIME handling only for /media/

Disabling MIME Type Detection

types { }
default_type application/octet-stream;

• All files downloaded
• Useful for secure file servers

Security Best Practices

Prevent MIME Sniffing

add_header X-Content-Type-Options nosniff;

Prevents browsers from guessing content type.

Correct JavaScript MIME Type

application/javascript js;

Avoids browser console warnings.

Common MIME-Related Issues

Problem	Cause
CSS not loading	Wrong MIME type
JS blocked	text/plain instead of JS
Images download	Incorrect mapping
Browser warnings	Missing nosniff

Debugging MIME Types

Check Headers

curl -I http://example.com/style.css

Expected:

Content-Type: text/css

Real-World Production Example

http {
    include mime.types;
    default_type application/octet-stream;

    server {
        listen 80;
        root /var/www/app;

        location / {
            try_files $uri $uri/ =404;
        }

        add_header X-Content-Type-Options nosniff;
    }
}

Common Mistakes

• Not including mime.types
• Wrong JS MIME (text/javascript in strict setups)
• Overriding default_type globally
• Relying on browser sniffing