Fix "Runaway argument" and "Paragraph ended before" in LaTeX

These errors mean a command’s argument was opened with { but never closed with }, so LaTeX kept reading until it hit a blank line or the end of the file. You will learn how to find the missing brace.

The message

When the argument runs into a blank line:

Runaway argument?
{fig:results for the details.
./main.tex:4: Paragraph ended before \@kernel@ref was complete.

When it runs to the end of the file:

Runaway argument?
{an unclosed bold group. \par A new paragraph starts here. \end {docu\ETC.
! File ended while scanning use of \textbf .

The line after Runaway argument? shows the start of the argument that was never closed. That is the place to look.

Why it happens

A missing } at the end of an argument, for example \ref{fig:results or \textbf{word.
A } typed as ) or ] by mistake.
A blank line inside an argument that does not allow paragraphs, such as \ref, \cite or \label.

Example

\documentclass{article}
\begin{document}
See Figure~\ref{fig:results for the details.

The next paragraph starts here.
\end{document}

Fix

Close the argument where it should end:

\documentclass{article}
\begin{document}
See Figure~\ref{fig:results} for the details.

The next paragraph starts here.
\end{document}

Help from Luzbase

The code editor highlights matching brackets and closes { for you as you type, which makes a missing } easier to spot.
For “File ended while scanning use of …”, the error summary in the Output panel shows the hint “A { or an argument is never closed. Check the braces before this point.”

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Too many }’s, the opposite problem
Common LaTeX errors