What does a 500 error mean?

A symptom, not a diagnosis

The 500 code only indicates that something went wrong server-side, without saying what. The actual cause can vary widely: a fatal PHP error in the code, a database that's unreachable or overloaded, a corrupted configuration file, a memory limit exceeded, or a module or plugin left in a bad state after an update.

For a seller, a 500 error can make all or part of the site unusable, including the checkout, which directly halts sales. Finding the exact cause is therefore the priority, not just noting that the error occurred.

Where to look for the cause

The precise cause shows up in the error logs: the application's log file (PrestaShop, WordPress) and the web server's error log (Apache or Nginx). Temporarily enabling debug mode also displays the error's technical detail directly on screen for the duration of the diagnosis.

The method then depends on the platform. For a shop, follow the diagnosis for the PrestaShop 500 error or for the WordPress critical error. For a method that works whatever the CMS, see where a 500 error comes from.

The 500 error among the other 5xx codes

The 500 code belongs to the server error family, whose codes start with 5. It differs from its closest neighbours:

• 502 Bad Gateway: an intermediary in front of the site received an invalid response from the application server.
• 503 Service Unavailable: the service is unavailable, deliberately or temporarily, during maintenance for instance.
• 504 Gateway Timeout: the intermediary waited too long for a response and gave up.

Those three are covered in 502, 503 and 504 errors. A 500, by contrast, usually means the program did start, then stopped before producing a response.