What is the INC file format?
An .inc file in the web context is an HTML fragment designed to be inserted into other pages by a web server using Server Side Includes (SSI). SSI originated around 1994 with the NCSA HTTPd server; Apache's mod_include module later became the dominant implementation and remains maintained in Apache 2.4.x.
The web server processes SSI directives written in HTML comment syntax - for example <!--#include virtual="/header.inc" --> - and substitutes the fragment into the assembled response before sending it to the browser. The browser never receives the .inc file directly; it only sees the merged HTML output.
Typical uses are site-wide reusable elements such as page headers, footers, and navigation bars. Because any change to the .inc file propagates instantly to every page that includes it, SSI offered a primitive form of server-side templating before PHP and other scripting languages became standard.
The .inc extension is a convention with no enforced format: the same extension is also used by PHP include files, assembler include files, and Delphi/Pascal source fragments. An .inc file intended for SSI is plain UTF-8 or ASCII text - an HTML fragment without <html>, <head>, or <body> wrappers. SSI is largely obsolete for new projects, replaced by PHP include/require, template engines such as Jinja2 and Twig, and static site generators such as Jekyll or Hugo.
Security & safety
RISK: LOWAn .inc file is plain text - it contains no executable binary code and is not a malware vector by itself. However, an .inc file containing PHP or SSI code processed by a server does execute on the server; a maliciously crafted .inc with server-side code could cause harm if uploaded to a server and included. As a file you download and open in a text editor: safe. The main risk is a web server misconfigured to serve .inc files directly (exposing database credentials in a config.inc, for example).
Format details
in a nutshell- PHP Include File - PHP developers commonly name included PHP code fragments with .inc extension (e.g. config.inc, db.inc); processed server-side by PHP, never served directly to browsers.
- Assembler/Pascal/Delphi Include File - Many programming languages (x86 assembler NASM/MASM, Pascal/Delphi, Fortran) use .inc for include files containing constants, macros, or shared declarations.
- Game/Engine Data Include - Game engines including GZDoom (DECORATE/ZScript), Quake/Source engine, and AutoHotkey use .inc for data or script fragments included into larger scripts.
Programs that open INC files
Windows4 apps
Microsoft Visual Studio
Freemium Open directly; supports .inc as HTML or code include depending on project context. 
Visual Studio Code
Open-source Open folder or drag file into VS Code. Associate .inc with HTML or PHP syntax for highlighting. 
macOS3 apps
Visual Studio Code
Open-source Open the .inc file; set language mode to HTML or PHP for syntax highlighting. 
Linux2 apps
Vim
Open-source vim file.inc - set ft=html or ft=php for syntax. Widely used in server-side contexts. Technical details
deep spec| File type | Plain text - HTML fragment (partial page content without structural wrappers) |
| MIME type | text/html (primary); text/plain (alternate) |
| Encoding | UTF-8 or ASCII - matches the encoding of the including page |
| Compression | None - uncompressed plain text |
| Encryption | None - access controlled at the web server level, not the file |
| Typical size | Under 10 KB (reusable HTML fragment such as a site header or footer) |
| Magic bytes | None - plain text file with no binary signature |
| SSI directive syntax | HTML comment syntax: <!--#include virtual="/path/file" --> or <!--#include file="relative/path" --> |
| Server processing | Apache mod_include or Nginx ngx_http_ssi_module processes directives and injects the fragment before sending the response to the browser |
| Browser visibility | Browser never receives the .inc file directly - receives only the fully assembled HTML response |
| IIS support | Supported via the IIS Server Side Includes (SSINC) module on Windows |
| Associated OS | Linux, Windows, macOS (any OS hosting Apache, Nginx, or IIS) |
| Common uses | Site-wide headers, footers, and navigation bars - HTML fragments reused across multiple pages |
| Superseded by | PHP include/require, Jinja2, Twig, and static site generators (Jekyll, Hugo, Next.js) for new development |
| Released | ~1994 (NCSA HTTPd server includes); Apache adopted and extended |
| Latest version | N/A - SSI is a static web technology; Apache mod_include still maintained in Apache 2.4.x |
| Open standard | Yes · royalty-free |
| Specification | httpd.apache.org |
INC conversions
Community Q&A
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