How do I fix 'Parse error: syntax error, unexpected' in WordPress?

The message names a file and a line number. Open that file with your host's file manager or SFTP (the WordPress admin is down too), download a copy, and look at that line and the one above it. If you just pasted a code snippet, remove it and save; the site comes back at once. Then add it again with straight quotes and a semicolon at the end of each line, or through a snippets plugin that checks code before running it.

Why does the error point to a line I did not change?

PHP reports the line where it gave up, not where the mistake is. A missing semicolon or closing bracket at the end of one line is reported on the next line, and a missing closing brace is often reported at the very end of the file as 'unexpected end of file'.

Can curly quotes break a WordPress site?

Yes. PHP only accepts straight quotes. Code copied from a blog post or a word processor often has curly quotes, which PHP reads as part of a word, so it stops with 'syntax error, unexpected identifier' and refuses the whole file. Retype the quotes as straight ones.

I got a syntax error right after updating a plugin. What happened?

If the error points inside that plugin's folder and mentions characters such as '?', '=>' or '|', the new version was written for a newer PHP than your server runs. Rename the plugin's folder in wp-content/plugins to switch it off and get the site back, then raise the site's PHP version in your host panel after a backup, or install the plugin version that matches your PHP.

More fixes

"Parse error: syntax error, unexpected ..." on a WordPress site

PHP, the language WordPress is written in, reads a whole file before it runs any of it. One wrong character - a missing semicolon, an extra brace, a curly quote pasted from a blog - and it refuses the entire file. If that file is your theme's functions.php, wp-config.php or an active plugin, every page and the admin go down together. The good news: the message names the exact file and line, and nothing in your content is lost. Below is a rebuilt example (not a real client), how to read the message, and the fix for each cause.

The shop page

What the checks found

First: read the message, then open the file outside WordPress

Find the full message. Depending on your host's settings you see either the raw line - Parse error: syntax error, unexpected ... in /home/.../functions.php on line 42 - or WordPress's own "There has been a critical error on this website" page. In the second case the full line is in your host's error log (cPanel: Metrics > Errors, or error_log in the site's folder), and the site's admin email usually has a message titled "Your Site is Experiencing a Technical Issue" that names it too.
Note the file and the line. The path tells you whose code it is: wp-content/themes/... is the theme, wp-content/plugins/name/... is that plugin, wp-config.php is the site's settings file. The line number is where PHP gave up, so the mistake is on that line or just above it - a missing ; or ) at the end of the previous line is reported on the next one.
Open the file with the host's file manager or SFTP, not the WordPress editor. The admin is down too, and the WordPress theme editor would not let you save the broken code anyway (since 2017 it tests a PHP change and rolls it back if it breaks the site). Download a copy of the file before you change anything.

The causes, most common first

A code snippet pasted with a mistake. A tutorial says "add this to your functions.php", and something got lost on the way: the last line, a closing brace, or the straight quotes, which a blog or a word processor turned into curly ones (‘ ’ “ ”). PHP only accepts straight quotes. Remove the block you pasted and save - the site comes back at once. Then add it again with straight quotes and every line ending in ;, or better, through the free Code Snippets plugin, which checks the code before it runs and switches off a snippet that breaks.
An edit made through the host's file manager or FTP. These save whatever you type, with no check. That is often how a snippet the WordPress editor refused still reached the site. Same fix: restore the copy you downloaded, or undo the last change.
A second <?php or some HTML pasted inside PHP. The message says unexpected '<' or unexpected token "<". A snippet that starts with <?php was pasted into a file that is already PHP. Delete the extra opening tag.
A plugin or theme that needs a newer PHP than your server runs. Right after updating or uploading one, the error points inside that plugin's own folder and says something like unexpected '?', unexpected '=>' or unexpected '|'. The plugin is written for PHP 8 and the host still runs 7.x. Rename the plugin's folder in wp-content/plugins to switch it off, then either move the site's PHP version up in the host panel (after a backup, and after checking your other plugins support it) or install the plugin version that matches your PHP.
A file only half uploaded. unexpected end of file in a plugin or theme file nobody edited usually means an FTP upload or an update was cut off. Delete that plugin's folder and install a fresh copy; your settings live in the database and stay.
An edit to wp-config.php. Adding a line such as a memory limit or debug setting with a curly quote or no semicolon takes the whole site down, including the recovery email. Restore the copy, or retype the new line with straight quotes and a ; at the end.

What you see, what it means, what it needs

What the message says	Usual cause	Usual fix
`unexpected identifier` or `unexpected variable` at the start of a line	Missing `;` or `)` at the end of the line before	Add it on the previous line
`unexpected identifier` next to words in quotes, or a curly quote in the message	Curly quotes from a blog or a document	Retype the quotes as straight `'` or `"`
`unexpected '}'` or `unexpected end of file` in a file you edited	A brace missing or one too many	Remove the pasted block, or match every `{` with a `}`
`unexpected '<'`	A second `<?php` or HTML inside PHP	Delete the extra opening tag
`unexpected '?'`, `'=>'` or `'\|'` inside a plugin you just updated	Plugin needs a newer PHP	Rename its folder; raise PHP or use the matching version
`unexpected end of file` in a file nobody touched	Upload or update cut off	Fresh copy of that plugin or theme

What not to do

Do not reinstall WordPress or restore last month's backup. The broken line is in one theme, plugin or settings file; a reinstall does not touch it, and a restore throws away this month's orders and posts.
Do not delete the whole functions.php to make the error go away. The theme needs the rest of that file; remove only what was added.
Do not paste snippets into the parent theme's functions.php at all. The next theme update wipes them out. Use a child theme or a snippets plugin.

Once you have the file and the line, the fix is usually one character or one pasted block. If you would rather hand it over, or you cannot get into the host's file manager, that is what the box below is for. Related: "There has been a critical error", a blank white screen, 500 Internal Server Error and a plugin conflict.