aux

.aux — Auxiliary File

Various (often associated with TeX/LaTeX) · 1980s

Developer
Various (often associated with TeX/LaTeX)
Category
Documents
MIME Type
text/plain
First Released
1980s
Open Format
Yes
File Signature
N/A (plain text, no fixed signature)
At a Glance
.aux
Auxiliary File

An AUX file is a supporting file used by LaTeX and TeX to manage cross-references, tables of contents, and other navigational elements during document compilation.

Reviewed on July 15, 2026
Compression
Plain text
Transparency
No
Editability
Low (for general users)
Best for
Intermediate typesetting data

Key Features

  • Stores intermediate data for document compilation.
  • Facilitates cross-referencing and navigation.
  • Essential for generating tables of contents and indices.
  • Typically a plain text format, but structured for machine processing.

Best For

  • Storing intermediate data for LaTeX document compilation.
  • Enabling complex referencing in academic papers.
  • Supporting the generation of navigational elements in long documents.

Less Ideal For

  • Storing final document content for general viewing.
  • Sharing documents with non-technical users.
  • Replacing primary document formats like PDF or DOCX.
  • Storing images or multimedia content.

Common Use Cases

  • Compiling LaTeX documents with cross-references.
  • Generating tables of contents automatically.
  • Creating indices and glossaries.
  • Managing citations for bibliographies.

How to Open It

  1. Open with a plain text editor like Notepad (Windows), TextEdit (macOS), or gedit (Linux).
  2. LaTeX distributions (e.g., TeX Live, MiKTeX) automatically process AUX files during compilation.
  3. Avoid direct manual editing unless you are intimately familiar with TeX/LaTeX internal structures.

What is a .aux file?

An AUX file is a supplementary file that holds auxiliary information for a primary document, most commonly generated by the TeX and LaTeX typesetting systems. It stores data like table of contents entries, cross-references, index terms, and citations that are needed to generate the final output. While not directly readable by humans in a meaningful way, it's crucial for the compilation process of documents that require complex structuring and referencing. It's part of the larger ecosystem of files used to produce professional-looking documents, especially in academic and technical fields.

Programs That Open .aux Files

PlatformProgram
WindowsTeX LiveFreeOfficial
MiKTeXFreeOfficial
Notepad++Free
macOSMacTeXFreeOfficial
TextEditFreeOfficial
LinuxTeX LiveFreeOfficial
geditFreeOfficial

Common Problems with .aux Files

⚠️ Document compilation errors after modifying AUX file.
Do not manually edit AUX files unless you are an expert. Recompile your LaTeX document, and the system will typically regenerate the AUX file correctly.
⚠️ AUX file contents are unreadable.
AUX files are not meant to be read by humans directly. They contain control sequences for LaTeX. If you need to see navigation elements, focus on the output PDF or the source `.tex` file.

Frequently Asked Questions

What is an AUX file used for?▼

An AUX file is used by TeX/LaTeX to store auxiliary information needed for document compilation, such as cross-references, table of contents entries, and index data.

Can I open an AUX file directly to read its content?▼

You can open it with a text editor, but the content is primarily machine-readable control sequences for LaTeX, not easily understandable by humans.

Do I need to keep my AUX files?▼

Yes, AUX files are typically required for subsequent compilations of your LaTeX document to ensure cross-references and navigation elements are correctly updated.

Technical Details

AUX files are typically plain text files, although their internal structure is specific to the program that generated them, primarily TeX-based systems. They contain control sequences and data used by the typesetter to build indices, bibliographies, and tables of contents in the final output document. The content is machine-readable for the typesetting engine but not intended for direct human interpretation.

Did You Know?

The AUX file is a crucial component in the multi-pass compilation process of LaTeX documents.
Its contents are regenerated by the TeX engine during each compilation cycle.

Security Information

AUX files are generally safe as they are plain text files containing metadata for document compilation. However, like any file, avoid opening them from untrusted sources if they were part of a larger, potentially malicious, document package.

Related Extensions

.TEX