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    Debugging a slow WordPress site with Query Monitor

    by Iain Thomson Project Lead

    A slow WordPress site can frustrate both site owners and visitors, leading to higher bounce rates and lower search engine rankings. Fortunately, identifying and resolving performance issues can be a manageable task with the right tools. In this blog post, we’ll guide you through the process of debugging a slow WordPress site using the Query Monitor plugin.

    Why is my WordPress site slow?

    Before diving into specific debugging steps, it’s important to understand the common factors that can slow down a WordPress site:

    • Web hosting: Poor quality hosting services can significantly affect your site’s speed.
    • WordPress configuration: Inefficient settings can cause your site to run slowly.
    • Page size: Large images and heavy content can drag down load times.
    • Bad plugins: Some plugins can be poorly coded or conflict with other plugins.
    • External scripts: These include ads, font loaders, and other third-party scripts.

    Query monitor

    Query Monitor is a powerful debugging tool for WordPress that provides detailed insights into database queries, PHP errors, hooks, and more. It’s an essential tool for identifying what’s slowing down your site.

    Features of Query Monitor

    • Database queries: See all database queries performed on the page, including the time each query takes.
    • PHP errors: View PHP errors, warnings, and notices.
    • Scripts and styles: Check which scripts and styles are being loaded.
    • HTTP API calls: Monitor outgoing HTTP requests.
    • Hooks and actions: See which hooks and actions are being triggered.

    Steps to debugging your slow WordPress site with Query Monitor

    1. Install and activate Query Monitor

    First, install the Query Monitor plugin from the WordPress repository:

    1. Go to your WordPress admin dashboard.
    2. Navigate to Plugins > Add New.
    3. Search for “Query Monitor”.
    4. Click Install Now and then Activate.

    2. Analyse performance metrics

    Once Query Monitor is activated, you’ll see a new menu item in the WordPress admin bar. Clicking this menu item will open the Query Monitor panel, where you can analyse various performance metrics.

    Database queries

    One of the most common causes of a slow WordPress site is inefficient database queries. Query Monitor displays all the database queries executed on the current page, highlighting the time each query takes.

    • Look for slow queries: Identify queries that take a long time to execute.
    • Check for duplicate queries: Multiple identical queries indicate inefficient code.

    PHP errors

    PHP errors, warnings, and notices can also slow down your site. Query Monitor lists all PHP errors occurring on the current page.

    • Fix errors: Address any errors, warnings, or notices to improve performance.

    Scripts and styles

    Heavy or unnecessary scripts and styles can affect load times. Query Monitor shows all the scripts and styles loaded on the current page.

    • Dequeue unnecessary scripts: Identify and remove scripts that are not needed.

    HTTP API Calls

    Excessive or slow HTTP API calls can delay page loading. Query Monitor provides details on all outgoing HTTP requests.

    • Optimise API calls: Reduce the number of API calls or improve their performance.

    Hooks and actions

    Query Monitor also shows which hooks and actions are running on the current page.

    • Identify heavy hooks: Look for hooks that take a long time to execute and optimise them.

    3. Identify problematic plugins and themes

    Plugins and themes can significantly impact your site’s performance. Using Query Monitor, you can pinpoint which plugins or themes are causing issues.

    • Deactivate and test: Temporarily deactivate suspected plugins and check if performance improves.
    • Review theme code: If your theme is causing issues, consider optimising its code or switching to a more efficient theme.

    4. Optimise your site

    After identifying the issues, take the following steps to optimise your site:

    • Upgrade hosting: If your hosting environment is inadequate, consider upgrading to a better plan or provider.
    • Optimise database: Regularly clean up your database using plugins like WP-Optimize.
    • Compress images: Use plugins like Smush to compress images without losing quality.
    • Enable caching: Implement caching using plugins like W3 Total Cache or WP Super Cache.
    • Use a CDN: Distribute your content via a CDN like Cloudflare to reduce load times.

    5. Monitor ongoing performance

    After making optimisations, continue to monitor your site’s performance using Query Monitor and other tools like Google PageSpeed Insights. Regular monitoring helps catch new issues early and maintain a fast site.


    Debugging a slow WordPress site requires a systematic approach to identify and resolve performance bottlenecks. Query Monitor is a powerful tool that provides detailed insights into various aspects of your site’s performance. By analysing database queries, PHP errors, scripts, styles, and more, you can pinpoint the exact causes of slowdowns and take steps to optimise your site. Regular maintenance and monitoring will ensure your WordPress site remains fast and responsive, providing a better experience for your visitors.

    Remember, a fast site is not just about good performance metrics; it’s about enhancing user experience and engagement. Happy debugging!