To debug a WordPress failure without exposing it to visitors, edit wp-config.php and add WP_DEBUG, WP_DEBUG_LOG, and WP_DEBUG_DISPLAY before the stop-editing line. The safest diagnostic combination for a site that people can visit is:
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define( 'WP_DEBUG', true );
define( 'WP_DEBUG_LOG', true );
define( 'WP_DEBUG_DISPLAY', false );
@ini_set( 'display_errors', 0 );Reproduce the problem, then inspect the newest entries in wp-content/debug.log (or the custom path you configured). Start with the first plugin, theme, file, function, and line named in the trace. Confirm the cause on staging, repair the component, and turn debugging off when finished.
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What each WordPress debug setting actually does
WP_DEBUG is the master switch. WordPress raises PHP error reporting to E_ALL when it is enabled, allowing notices, warnings, deprecations, and fatal errors to be captured. The other two constants have no effect unless this switch is true.
| Setting | Purpose | Normal diagnostic value | Important limitation |
|---|---|---|---|
WP_DEBUG |
Turns on WordPress debugging and broad PHP error reporting. | true while investigating on development or staging. |
Do not leave it enabled on a public production site after diagnosis. |
WP_DEBUG_LOG |
Writes errors, warnings, notices, deprecations, and messages sent through PHP error_log() to a file. |
true for the default wp-content/debug.log, or a valid file path. |
It does nothing when WP_DEBUG is false. |
WP_DEBUG_DISPLAY |
Controls whether messages are inserted into generated HTML. | false when visitors must not see diagnostic output. |
It does nothing when WP_DEBUG is false; PHP display settings can also affect output. |
display_errors |
PHP-level switch that can print errors directly in the response. | Set to 0 while collecting logs on a live-facing site. |
It is separate from the WordPress constants, so disable both layers. |
Use real PHP booleans. Write true and false without quotation marks. A value such as 'false' is a non-empty string, which PHP treats as truthy and can produce the opposite behavior from what you intended.
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Choose the right environment before editing configuration
Debugging changes the way PHP reports problems and can create a file containing paths, queries, request data, and stack traces. A local copy or staging site is the preferred place to trigger failures. If the problem exists only on production, take a backup and use the least revealing settings: log to a protected location, keep display output disabled, reproduce once, and remove the diagnostic material immediately afterward.
Back up the files and database
Save a known-good copy of wp-config.php before changing it. A syntax mistake in this file can prevent WordPress from loading. A current database and file backup gives you a recovery path if a plugin, theme, or configuration change causes a second failure.
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Plan how you will read the log before enabling it. SSH, SFTP, or a hosting control-panel file manager are appropriate authenticated methods. Do not assume that a browser should be able to open debug.log; a web-accessible log can disclose information to anyone who finds its URL.
Enable WP_DEBUG and file logging
Open the WordPress root directory and edit wp-config.php. Insert the following block before the line that says /* That's all, stop editing! Happy blogging. */:
define( 'WP_DEBUG', true );
define( 'WP_DEBUG_LOG', true );
define( 'WP_DEBUG_DISPLAY', false );
@ini_set( 'display_errors', 0 );- Save the file without changing its PHP opening tag or adding characters before it.
- Load the site once to check that WordPress still responds.
- Trigger the specific failure instead of clicking around randomly. Use the same page, form submission, Ajax action, REST request, or scheduled task that originally failed.
- Record the approximate time and request you made. This makes the corresponding log entries easier to identify.
With this configuration, WordPress records diagnostic messages but keeps them out of normal page HTML. The final ini_set() line explicitly turns off PHP’s direct error display, which is an additional safeguard when server-level settings would otherwise print messages.
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Find the debug.log file or set a custom path
When WP_DEBUG_LOG is true, WordPress uses wp-content/debug.log by default. The path is relative to the WordPress installation, not necessarily the server’s document root. Multisite, relocated content directories, and unusual hosting layouts can therefore make the file appear somewhere other than the directory you first expect.
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Use a custom file path
You may replace true with a valid path:
define( 'WP_DEBUG_LOG', '/protected/path/wordpress-debug.log' );Use a location that the PHP process can write to and that the web server cannot serve as a public download. An absolute path outside the public document root is preferable when your host permits it. If the file never appears, check the directory’s ownership and permissions, available disk space, and the PHP user that runs the request. A path that looks valid to you may be unwritable to that process.
When no log is created
- Confirm that
WP_DEBUGis exactlytrue; the companion constants are inert without it. - Check that the edited
wp-config.phpis the one used by this installation. Some hosts place it one directory above the web root. - Verify that the configured directory exists and is writable by PHP.
- Look for a hosting-level PHP error log if WordPress cannot write its own file.
- Make a harmless test request after saving, then inspect the file’s modification time rather than relying on an old entry.
Reproduce the failure in a controlled way
A log is useful only when you can connect an entry to a request. Clear or archive an old log on staging, enable the settings, and perform one reproducible action at a time. For a front-end problem, load the exact URL and repeat the click that triggers it. For an editor problem, open the affected post type and perform the failing save. For an integration, send the same webhook or REST request with the same authentication and payload. For a background task, wait for the relevant WP-Cron event or run it through the site’s normal scheduler.
Include off-screen requests
Ajax calls, REST requests, and WP-Cron jobs often fail without placing an error in the HTML you can see. A blank Ajax response, a failed block-editor request, or a task that silently stops can still write a useful entry to the log. Note the request time, endpoint, user action, and—when available—the HTTP status shown by your browser’s network panel or task monitor.
Avoid changing several variables at once
Do not update a plugin, switch themes, edit PHP, and alter server settings in one pass. Each change destroys your ability to tell which component fixed or caused the problem. Capture the original error first, then make one controlled change and reproduce the same request.
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Read the newest entries first
Open the log through SSH, SFTP, or your hosting file manager and start at the bottom, where the newest entries normally appear. For each relevant entry, record five details:
- Timestamp: match it to the request you just reproduced. Server and site time zones may differ.
- Severity: distinguish a
PHP Fatal errorfrom a warning, notice, deprecation, or informational message. - Message: identify the missing class, undefined function, type mismatch, database error, or other immediate symptom.
- File and line: note the exact PHP file and line reported by the engine.
- First application component in the trace: find the first plugin, theme, or custom-code function called in the stack, not merely the WordPress core function that eventually stopped.
The last line is not always the root cause. A plugin can pass invalid data into a core function, so the fatal line may be in core while the first application-specific caller identifies the component that supplied the bad value. Read upward through the trace until you find that boundary.
Interpret common severities
- Fatal error: execution stopped for that request. Look for an incompatible function, missing class, parse error, exhausted memory, or uncaught exception.
- Warning: execution may continue, but a file, value, or operation was not handled as expected. Repeated warnings can precede a later fatal error.
- Notice: code accessed something questionable, such as an undefined index. Notices may reveal a compatibility problem even when the page still loads.
- Deprecated: code uses an API that a current PHP or WordPress version plans to remove. Treat recurring deprecations as upgrade work, not harmless noise.
Read a cluster of entries around the same timestamp together. One underlying failure can produce several follow-on warnings; fixing the earliest meaningful application error is usually more productive than chasing every consequence.
Trace a critical error back to a plugin, theme, or custom code
Once you have the file, line, and first application function, map it to the request that failed. A file under a plugin directory points to that plugin’s code; a file under the active theme points to the theme or custom snippets; a file in a must-use plugin or hosting integration may not appear in the normal Plugins screen.
Confirm the suspect on staging
- Clone or restore the site to staging, preserving the same WordPress, PHP, plugin, theme, and database versions if possible.
- Enable logging there and reproduce the same request.
- Deactivate only the suspected plugin or switch temporarily to a bundled theme.
- Repeat the request and compare the new log.
- Reactivate or restore the component, then test the next suspect if the error remains.
Confirmation means the same failure disappears when one component is isolated and returns when that component is restored. If disabling a plugin merely hides the symptom, inspect dependencies, hooks, and the data passed into the failing function before declaring the cause solved.
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Handle a locked-out administrator
If a fatal plugin or theme error prevents normal access, use your host’s file manager or database tools to deactivate the offending component, then restore access and investigate on staging. Renaming a plugin directory is a temporary emergency measure, not a repair; WordPress will treat the plugin as missing until the directory name is restored.
Understand Recovery Mode and fatal-error handling
WordPress 5.2 introduced Recovery Mode to intercept a fatal error from a plugin or theme and give an administrator a protected session in which to deactivate the failing component. It is designed to keep one extension failure from permanently locking every user out.
Recovery Mode can make a public failure appear less severe than it is because the administrator’s session receives a special recovery flow while ordinary visitors may see a generic error. Check the log and the recovery notice rather than assuming the issue has disappeared.
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For development diagnosis, the WordPress configuration handbook documents:
define( 'WP_DISABLE_FATAL_ERROR_HANDLER', true );This disables the fatal-error handler so the underlying fatal can remain visible to developers. Use it only in a controlled development environment while you need the complete failure. Do not add it casually to a public production site, where it can remove the protection Recovery Mode provides.
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Separate display debugging from log-only debugging
| Approach | What the requester sees | Where evidence goes | Best use | Main risk |
|---|---|---|---|---|
WP_DEBUG=true, WP_DEBUG_DISPLAY=true |
Messages may be printed in generated HTML. | Possibly the response, and a log if logging is enabled. | Local development when the developer controls the browser. | Paths, queries, credentials, and stack details can leak to visitors or be cached. |
WP_DEBUG=true, WP_DEBUG_LOG=true, WP_DEBUG_DISPLAY=false |
Normal pages stay free of diagnostic output. | wp-content/debug.log or the configured custom path. |
Staging and carefully controlled production diagnosis. | The file is sensitive and must be protected and removed after use. |
WP_DEBUG=false |
No WordPress debug output is enabled by these constants. | No WordPress debug log from this configuration. | Normal production operation after the issue is understood. | You lose the extra evidence if you turn it off before reproducing the problem. |
Even with WP_DEBUG_DISPLAY false, a server-level PHP configuration can print errors. Keep @ini_set( 'display_errors', 0 ); in the temporary diagnostic block when you need to guarantee that generated pages do not expose messages.
Investigate database, scripts, and deeper code paths
The basic log identifies many PHP failures, but not every WordPress problem is a single fatal line. Once the immediate cause is isolated, the official WordPress debugging workflow also includes specialized options:
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1Repair Windows errors before they cause bigger problems2Scan for outdated or missing drivers - takes under a minute3Clear out junk files and repair common Windows errorsSCRIPT_DEBUG: loads development versions of core JavaScript and CSS instead of minified assets, which helps when an editor or interface fails in the browser.SAVEQUERIES: records database queries and timing for query analysis. Enable it only in a controlled environment because it consumes memory and can expose query data.- Debugging plugins: can add request, hook, and query inspection, but treat their output as sensitive and remove them after diagnosis.
- Automated tests: reproduce a regression repeatedly without relying on manual clicks.
- Step debugging: a debugger can pause execution and inspect variables when a log line is too general to explain the bad input.
These tools complement, rather than replace, the first reproduction and log review. Add one diagnostic layer at a time so its output remains attributable to the request you are testing.
Production security and cleanup
Debug logs and visitor-visible errors can disclose absolute server paths, database structure, usernames, request payloads, plugin details, and values passed to third-party services. WordPress Site Health treats visitor-visible errors and potentially public logs as security risks for that reason.
While collecting diagnostics
- Keep
WP_DEBUG_DISPLAYfalse and PHPdisplay_errorsoff. - Use an authenticated file method to read the log.
- Prefer a non-public custom path when your host supports one.
- Limit the diagnostic window and avoid publishing screenshots that contain paths, tokens, or user data.
- Restrict access to staging and production administration accounts that need the evidence.
After the cause is understood
- Apply and test the repair on staging first.
- Deploy the smallest confirmed change to production.
- Set
WP_DEBUGtofalseand remove temporary overrides such asWP_DISABLE_FATAL_ERROR_HANDLER. - Remove or securely archive
debug.logand any custom log file. Do not leave old logs publicly reachable. - Repeat the original request and verify both that the feature works and that no new diagnostic output is exposed.
Do not simply truncate a log and leave debugging enabled indefinitely. A quiet day does not prove the configuration is safe; a later request can write sensitive data without anyone noticing.
Quick diagnosis table
| Symptom | First check | Likely next action |
|---|---|---|
| Visitors see PHP paths or warnings | WP_DEBUG_DISPLAY and display_errors. |
Set both display controls off, keep logging only if needed, and invalidate cached error pages. |
No wp-content/debug.log |
Master switch, edited config file, path permissions, and disk space. | Correct the path or permissions and reproduce a request. |
| Page loads but an Ajax action fails | Newest entries at the time of the network request. | Use the log and request endpoint together; the error may never appear in page HTML. |
| Critical error after an update | Fatal entry’s file, line, and first plugin/theme caller. | Use Recovery Mode or temporarily deactivate the component, then test version compatibility on staging. |
| Many warnings obscure the failure | Timestamp and earliest meaningful application error. | Group entries by request and fix the first component-specific cause before follow-on messages. |
| Developer needs the full fatal locally | Whether Recovery Mode is intercepting it. | On development only, consider WP_DISABLE_FATAL_ERROR_HANDLER true; restore the default afterward. |
A repeatable WordPress debugging checklist
- Back up the site or switch to a representative staging copy.
- Insert the four-line log-only configuration before the stop-editing comment in
wp-config.php. - Use unquoted boolean values and verify that the file remains valid PHP.
- Reproduce one known failure and note its time, URL, action, or scheduled event.
- Open the newest log entry through SSH, SFTP, or an authenticated file manager.
- Record severity, message, file, line, and the first plugin, theme, or custom function in the trace.
- Isolate one component at a time on staging and reproduce the same request.
- Use specialized tools only if ordinary log evidence cannot distinguish the cause.
- Repair and retest the confirmed cause.
- Turn
WP_DEBUGoff, remove temporary fatal-handler overrides, and delete or protect the log.
This sequence gives you the useful part of WordPress debugging—precise evidence tied to a reproducible request—without turning diagnostic output into a data leak or leaving a temporary development setting on the production site.
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