A .tex file is a LaTeX document: plain text with commands such as \section and \begin{equation} that say how it is to be laid out. LaTeX, through pdflatex, xelatex, lualatex or an editor such as Overleaf, TeXstudio or TeXworks that runs them, turns it into a PDF. On the way it writes a crowd of other files with the same name: main.aux, main.log, main.toc, main.out and, with a bibliography, main.bbl and main.blg. They are its notes to itself between runs, which is why a folder holding one paper soon holds a dozen files nobody asked for.
This page reads all of them. A .tex file is shown as its source with comments greyed out and an outline of its parts, chapters, sections and slides that jumps to each one, and every formula in it drawn as it would look, from the inline $x^2$ to aligned equations, with a link that opens it in the Equation Editor. An .aux file, the most puzzling of the helpers, is set out as the labels with their numbers, pages and titles, the sources cited, the contents entries and the bibliography settings. A .bib file becomes a table you can search, copy from and save as CSV, and a .log file puts its errors and warnings first, each with its line number. It is free to use, with no account and no upload limit, and it runs entirely in your browser: nothing is uploaded, and while the page stays open, a feature you have already used keeps working offline.
It reads LaTeX's files; it is not LaTeX. It does not compile a document or make its PDF, run BibTeX or Biber, or follow \input to other files, and formulas are drawn with MathJax, which knows LaTeX's maths, the AMS packages and chemistry written with mhchem's \ce and \pu, but not drawings (TikZ), tables, or other packages it does not have. For a PDF, build the document in Overleaf or in a TeX system such as TeX Live or MiKTeX.
The first five, .tex to .bib, are files you write or install; the rest are made again by the next build, so they can be deleted whenever the folder needs tidying.
- What is an .aux file?
- An .aux (auxiliary) file is a helper file LaTeX writes each time it builds a document, named like the document (thesis.aux beside thesis.tex). LaTeX can only know the number and page of a section, figure or equation once it has set it, so on each run it writes them to the .aux file and reads them back on the next, which is how \ref and \cite turn into numbers. It also records the sources cited, for BibTeX, and the table of contents entries. Drop one here to see all of that set out.
- Can I delete .aux, .log and the other LaTeX files?
- Yes, all except the ones you wrote: keep the .tex, the .bib, and any .sty, .cls or pictures the document uses. The .aux, .log, .toc, .out, .bbl, .blg and the rest are written again the next time the document is built, which may then need two or three runs (or one with latexmk) to get every reference right. Most editors have a menu item for it, such as Clean auxiliary files in TeXstudio, and latexmk -c does it from the command line. Keep the .bbl when you send the source to a journal or to arXiv.
- How do I open a .tex file?
- A .tex file is plain text, so Notepad, TextEdit or any code editor opens it, and this page shows it with its outline and formulas. To edit it and make the PDF you need LaTeX: Overleaf in a browser, or a TeX system (TeX Live, MiKTeX, or MacTeX on a Mac) with an editor such as TeXstudio or TeXworks.
- Can this page turn my .tex file into a PDF?
- No. Making the PDF takes LaTeX itself, with the packages and fonts the document asks for, and this page does not run it. It reads the file and draws its formulas so you can see what is in it; build the PDF in Overleaf or a TeX system.
- Why does my PDF show ?? where a number should be?
- The numbers come from the .aux file, which is only up to date after a second run of LaTeX. Build the document again; if the ?? stays, the \label it points to is missing or misspelled. Drop the .log here: an undefined reference is listed with the line it is on, and the log says when LaTeX wants another run. The .aux file's label list shows which labels exist.
- Why is a formula shown in red, or not as it is in my PDF?
- Formulas are drawn by MathJax, one at a time and without the rest of the document. It knows LaTeX's maths and the AMS packages, and commands the document defines itself with \newcommand or \DeclareMathOperator are filled in first, but a command defined in another file or a package it does not have is shown in red. Spacing, fonts and equation numbers can also differ from the PDF.
- How do I turn a .bib file into a spreadsheet?
- Drop it here and click Download CSV: you get one row for each entry, with its key, type, authors, title, year, journal, book title, publisher, volume, number, pages, DOI, URL and ISBN, which Excel, Google Sheets or Numbers open. Search first to save only the entries that match.
- Why does my .log or .toc file say it is not a LaTeX file?
- Other programs use the same names: most .log files are logs of other programs, a World of Warcraft add-on keeps a .toc file, a DVD subtitle index is an .idx, and a Visual Basic class module is a .cls. This page only opens those when their contents are LaTeX's, and otherwise says so; the File Opener works out from its contents what such a file is.
- Is my paper or thesis uploaded anywhere?
- No. The file is read by your browser on your own device, so an unpublished paper or thesis stays on it. The formulas are drawn by a copy of MathJax served from this site, with nothing sent back.