Debug Bar plugin review and common issues

Debug Bar’s SQL query panel requires SAVEQUERIES to be enabled in wp-config.php. Add the following to wp-config.php before the “That’s all” comment: define(“SAVEQUERIES”, true); This constant tells WordPress to store all database queries for debugging. Also ensure WP_DEBUG is set to true for full error reporting. Note that SAVEQUERIES adds overhead to every database query — only enable it during active debugging sessions and disable it afterwards.

Debug Bar only displays when: (1) the user is logged in as an administrator; (2) WP_DEBUG is set to true in wp-config.php. If either condition is false, the Debug Bar menu does not appear. Verify WP_DEBUG = true in wp-config.php. Also check if a CSS conflict with your admin theme is hiding the Debug Bar button — use browser DevTools to inspect the admin bar area for a hidden Debug Bar element.

Debug Bar Console provides an in-browser JavaScript console for executing code in the WordPress context. Conflicts can occur with JavaScript debugger extensions or other admin plugins that modify the browser console. Try: (1) disabling browser extensions (particularly developer tools extensions); (2) testing in a different browser; (3) checking browser DevTools Console for the specific error message — JavaScript syntax errors in the eval’d console code are user error; JavaScript errors from Debug Bar Console itself indicate a plugin conflict or browser compatibility issue.

Create a class that extends Debug_Bar_Panel. Implement the init() method (called on each page load for setup), the prerender() method (called before render, good for data collection), and the render() method (outputs the panel HTML). Add the panel to Debug Bar via add_filter(“debug_bar_panels”, function($panels) { $panels[] = new My_Custom_Panel(); return $panels; }); This pattern allows plugin developers to surface plugin-specific debug data alongside Debug Bar’s standard panels.

The most valuable Debug Bar add-ons: (1) Debug Bar Console — execute PHP/jQuery code in the browser against WordPress context; (2) Debug Bar Actions and Filters — shows hooks fired on the current page (similar to Query Monitor’s hooks panel); (3) Debug Bar Cron — displays scheduled WP-Cron events and their next run times; (4) Debug Bar Transients — shows stored transients with expiration times; (5) Debug Bar Constants — lists all defined PHP constants active during the request. Install only the add-ons relevant to your current debugging task to minimize admin overhead.

Query Monitor is the recommended choice for most WordPress developers in 2025. It provides all the functionality of Debug Bar plus database query caller attribution, hook tracing, HTTP API logging, REST API inspection, and block editor data — without requiring WP_DEBUG or SAVEQUERIES to be enabled in wp-config.php. Debug Bar is a simpler alternative for developers who want a focused tool with lower information density, or who need the specific capabilities of Debug Bar add-ons not available in Query Monitor.

Debug Bar itself adds minimal overhead to the page response — it collects data during the request and displays it in the admin bar. The most significant performance impact comes from enabling SAVEQUERIES (required for SQL query display), which stores all database queries in PHP memory throughout the request. On pages with many queries, this can add measurable memory and time overhead. Disable SAVEQUERIES when not actively using Debug Bar’s query panel.

Yes, that can happen, especially on older sites with many plugins. This usually happens when the plugin, theme, and add-ons are updated out of sequence. In most cases, testing on staging catches the issue before it reaches the live site. From experience, backups and changelog reviews save a lot of cleanup time.

Start by checking whether another plugin already does the same job. In most cases, overlap is what creates avoidable conflicts and performance issues. A common issue is installing a plugin because it looks convenient without checking the stack first. From experience, a short compatibility review avoids most of the pain later.