Use Query Monitor to diagnose a slow WordPress request. It shows the SQL queries, PHP timing, HTTP API calls, errors, scripts and styles generated by one page load, then helps you trace expensive work to a plugin, theme, WordPress core or calling function. Start with its timeline, move to Queries by Component, and verify the result after each change.
What Query Monitor can tell you
Query Monitor is a free developer-tools panel for WordPress and WooCommerce. Its toolbar summary reports the current request’s page-generation time, peak memory, total SQL time and query count.
The panel can identify slow, duplicate and erroneous database queries and group them by query type, plugin, theme, WordPress core component or calling function. This makes it useful when you need to answer, “Which plugin is making this page slow?”
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| What you see | What it helps answer |
|---|---|
| Page-generation time and peak memory | Is this request expensive on the server, and is memory a concern? |
| Total SQL time, query count and individual statements | Is database work a significant part of this request? |
| Queries by Component | Which plugin, theme or core component accounts for the aggregate query time? |
| Timeline | When during the request does the work happen? |
| HTTP API Calls | Is server-side code waiting for another service? |
| PHP errors, scripts and styles | Could warnings or front-end assets explain the remaining slowdown? |
Install it and reproduce the problem safely
- In WordPress, open Plugins → Add New Plugin, search for Query Monitor, install it from WordPress.org and activate it.
- Log in with an Administrator account on a single-site installation, or a Super Admin account on Multisite. The documentation says the Query Monitor menu then appears in the admin toolbar.
- Open the same page, form submission, checkout step or AJAX-triggering action that feels slow. Reproduce the issue while logged in, rather than judging the toolbar on a different request.
- Select the Query Monitor toolbar menu. Record the page-generation time, peak memory, total SQL time and total query count before changing anything.
Output is normally access-controlled: Administrators see it on single-site installations and Super Admins on Multisite. Query Monitor also documents an authentication-cookie option for viewing output while logged out or as a non-Administrator. Do not assume ordinary visitors can see the panel.
Read the request in the right order
1. Start with the timeline
Open the timeline before chasing an individual query. It places the request’s work in sequence, helping you distinguish database activity from PHP execution and other stages. Version 4 introduced the timeline and client-side Preact panel rendering. Version 4.0.7 added database queries to the timeline even when db.php is not installed.
2. Use Queries by Component to find likely owners
Go to Queries → Queries by Component. Query Monitor aggregates queries by plugin and theme and sorts components by total query time. A component with many inexpensive queries can matter as much as one with a single slow statement, so consider total time and frequency together.
Expand the component and follow a query to its responsible code or calling function. That trace is evidence for investigation, not automatic proof that the plugin is the sole cause. Check whether the query is expected, whether it runs repeatedly, and whether another component or the database itself is involved before disabling or removing anything.
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Look for slow, duplicate or erroneous statements and note their query type and call site. A single outlier can expose a defect, but aggregate SQL time, the timeline and the number of repeated statements provide the context needed for a sound decision.
Check bottlenecks that are not SQL
HTTP API calls
Open HTTP API Calls. A plugin or theme may make server-side requests to an external service, and waiting for those requests can increase page-generation time even when SQL is fast. Examine the destination, duration, frequency and calling component before changing credentials, timeouts or integrations.
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PHP errors and warnings
Review the PHP errors and warnings panel. The Query Monitor guide notes that warnings indicate code is not operating as expected; logging and repeated error handling can add work to a request. Fix the underlying notice, warning or fatal error in the responsible code rather than hiding the diagnostic output.
Scripts and styles
If server page-generation time is acceptable but the page still feels slow to visitors, inspect scripts and styles. Large, render-blocking or unnecessary front-end assets affect browser loading separately from the PHP request. Query Monitor can show what was enqueued, but browser performance tools are still needed to measure network transfer, rendering and interaction delays.
Compare changes without mistaking Query Monitor for history
Query Monitor displays diagnostic information for the current page load. Its documentation explicitly states: “All of the information shown by Query Monitor is for the current page load.” It does not provide historical performance data.
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- Choose one URL and one reproducible action.
- Capture the same toolbar and panel values before the change.
- Make one targeted change, such as updating a plugin, removing an unnecessary query or correcting an external request.
- Repeat the identical request under comparable conditions and compare the new values yourself.
- Test logged-in and cache-hit behavior separately when both matter to your site.
This repeat-and-compare process gives you a practical before-and-after check, but it is not a historical report generated by Query Monitor. Avoid claiming a percentage improvement unless you measured it under defined, repeatable conditions.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.Use object caching when repeated database work is the problem
WordPress’s default object cache does not persist between page loads. A persistent object cache can retain eligible results across loads, reducing repeated work when the application and hosting environment support it. The Query Monitor guide names Redis and Memcached as possible drivers and recommends asking your hosting provider about setup.
Object caching is not a universal requirement. Confirm compatibility, memory limits, invalidation behavior and deployment support with your host and application before enabling it. Query Monitor can help you see the repeated queries; it does not configure a Redis or Memcached service for you.
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Interpret results without blaming the wrong component
- High total SQL time: investigate the component aggregate, repeated statements, indexes and data volume with your host or developer.
- Low SQL time but a slow request: examine the timeline, PHP work, HTTP API calls and PHP warnings.
- Fast server response but slow visual loading: inspect scripts, styles, images and browser-side behavior.
- One slow query: treat it as a lead. Confirm its frequency, call site and contribution to total request time before changing the associated plugin.
- Different results for logged-in and public users: account for authentication, page caching and conditional plugin behavior.
Query Monitor itself collects diagnostic data during requests. A WordPress.org support report describes memory exhaustion on one site with many queries; that is an individual report, not a measured rate for WordPress sites generally. On constrained or unusually busy development requests, watch the memory figures in the toolbar and avoid treating the diagnostic panel as free of overhead in every environment.
Choosing a monitoring tool
The official WordPress.org tag page lists Query Monitor and alternatives or add-ons such as DebugPress: https://wordpress.org/plugins/tags/query-monitor/. The available evidence does not establish a reliable head-to-head performance test, so compare tools by the questions your team needs answered:
- Can it show individual SQL statements and flag slow, duplicate or erroneous queries?
- Can it attribute work to a plugin, theme, core component and calling function?
- Does it expose non-database bottlenecks such as HTTP requests and front-end assets?
- Does it support your WordPress and PHP versions?
- Does it retain historical data, or only describe the current request?
Query Monitor’s verified scope is detailed, current-request diagnostics; it should be paired with external logs, real-user monitoring or browser tooling when you need long-term trends.
Quick Recap
Official references
- Query Monitor on WordPress.org
- Query Monitor: How to use Query Monitor
- WordPress.org Query Monitor tag results
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