Code Review: What We Look For VIP platform specific

This document is for sites running on VIP.

Learn more


Overview #

Every line of code that is committed to VIP is reviewed by the VIP Team. We don’t do in-depth code reviews to add more time to or delay your launch schedules. We do these lengthy code reviews to help you launch successfully.

The goal of our reviews is to make sure that on launch, your site will be:

  • Secure, because pushing a site live with insecure code presents a liability to you and your whole userbase;
  • Performant, because going live and finding out that your code can’t handle the traffic levels that your site expects puts most of your launch efforts to waste.

We also review for development best practices to make sure that your site will continue to live on without significant maintenance costs or major issues when WordPress is upgraded.

Before submitting any code for review, please be sure to look through our Code Review Guidelines and Best Practices Documentation. The following is a checklist of items our VIP engineers look for when reviewing. Please note that this is a living list and we are adding and modifying it as we continue to refine our processes and platform.

We also have more documentation on topics that come up often such as:

We hope that by sharing this document, you will be able to better prepare your code for peer review.

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Blockers #

Blockers are items that need to be fixed before being committed to Here’s a partial list of what can be a blocker:

Direct Database Queries #

Thanks to WordPress’ extensive API, you should almost never need to query database tables directly. Using WordPress APIs rather than rolling your own functions saves you time and assures compatibility with past and future versions of WordPress and PHP. It also makes code reviews go more smoothly because we know we can trust the APIs. More information.

Additionally, direct database queries bypass our internal caching. If absolutely necessary, you should evaluate the potential performance of these queries and add caching if needed.

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Database alteration #

The WordPress schema and API’s are robust enough to handle almost any requirements. The core API’s are easy to use and add a performance layer to ensure that your site will run smoothly.

Creating or deleting tables, and schema modifications are not allowed. Themes and plugins should use the existing database tables and structure. Plugins which create custom database tables during installation cannot be used. We recommend finding an alternative that doesn’t use custom database tables or rewriting the plugin to use Custom Post Types, Custom Taxonomies, post meta, etc. — all of which are incredibly flexible as an alternative to custom database tables.

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Filesystem writes #

Make sure that your code and plugins do not write to the filesystem. Since the network is distributed across many servers in multiple data centers, file system writes won’t work how they would in a single server environment. The core WordPress upload functions can handle any uploads you need to do.

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Validation, Sanitization, and Escaping #

Your code works, but is it safe? When writing code for the VIP environment, you’ll need to be extra cautious of how you handle data coming into WordPress and how it’s presented to the end user. Please review our documentation on validating, sanitizing, and escaping.

$_GET, $_POST, $_REQUEST, $_SERVER and other data from untrusted sources (including values from the database such as post meta and options) need to be validated and sanitized as early as possible (for example when assigning a $_POST value to a local variable) and escaped as late as possible on output.

Nonces should be used to validate all form submissions. This includes parts in the code such as a save_post where the user’s intent has ostensibly already been verified since this code can be run in unexpected contexts, for example on the jobs servers, as a WP CLI command, as a syndication task or other task. In these cases it’s often a protection for the code to only be run when it was intended to run.

Capability checks using current_user_can() need to validate that users can take the requested actions.

It’s best to do the output escaping as late as possible, ideally as it’s being outputted, as opposed to further up in your script. This way you can always be sure that your data is properly escaped and you don’t need to remember if the variable has been previously validated.

Here are two examples. In order to keep this straight forward, we’ve kept them simple. Imagine a scenario with much more code between the place where $title is defined and where it’s used. The first example is more clear that $title is escaped.

$title = $instance['title'];

// Logic that sets up the widget

echo $before_title . esc_html( $title ) . $after_title;


$title = esc_html( $instance['title'] );

// Logic that sets up the widget

echo $before_title . $title . $after_title;

More information.

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Arbitrary JavaScript and CSS stored in options or meta #

To limit attack vectors via malicious users or compromised accounts, arbitrary JavaScript cannot be stored in options or meta and then output as-is.

CSS should also generally be avoided, but if absolutely necessary, it’s a good idea to properly sanitize it. See art-direction-redux, for an example.

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Uncached Functions #

WordPress provides a variety of functions that interact with the database, not all of which are cacheable. To ensure high performance and stability, please avoid using any of the functions listed on our Uncached Functions list.

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Whitelisting values for input/output validation #

When working with user-submitted data, try where possible to accept data only from a finite list of known and trusted values. For example:

$possible_values = array( 'a', 1, 'good' );
if ( ! in_array( $untrusted, $possible_values, true ) )
die( "Don't do that!" );

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Encoding values used when creating a url or passed to add_query_arg() #

Add_query_arg() is a really useful function, but it might not work as intended.
The values passed to it are not encoded meaning that passing

$my_url = 'admin.php?action=delete&post_id=321';
$my_url = add_query_arg( 'my_arg', 'somevalue&post_id=123', $my_url );

You would expect the url to be: admin.php?action=delete&post_id=321&somevalue%26post_id%3D123
But in fact it becomes: admin.php?action=delete&post_id=321&somevalue&post_id=123

Using rawurlencode() on the values passed to it prevents this.

Using rawurlencode on any variable used as part a the query string, either by using add_query_arg() or directly by string concatenation will also prevent parameter hijacking.

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Prefixing functions, constants, classes, and slugs #

Per the well-known WordPress adage: prefix all the things.

This applies to things obvious things such as names of function, constants, and classes, and also less obvious ones like post_type and taxonomy slugs, cron event names, etc.

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Using Theme Constants #

On, there are a few circumstances where services and plugins will load your theme’s functions.php even if your theme isn’t directly accessed (such as our Post-by-email service, our jobs servers, the wp-api etc)

This means constants such as TEMPLATEPATH and STYLESHEETPATH will not be defined or available, and using them in your theme will likely result in fatal errors.


Instead of TEMPLATEPATH, use get_template_directory()
Instead of STYLESHEETPATH, use get_stylesheet_directory()

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Creating a session writes a file to the server and is unreliable in a multi-server environment.

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Not checking return values #

When defining a variable through a function call, you should always check the function’s return value before calling additional functions or methods using that variable.

function wpcom_vip_meta_desc() {
   $text = wpcom_vip_get_meta_desc();
      if ( !empty( $text ) && ! is_wp_error( $text ) {
         echo "n<meta name="description" content="$text" />n";

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Order By Rand #

MySQL queries that use ORDER BY RAND() can be pretty challenging and slow on large datasets. You can either retrieve 100 posts and pick one at random or use this helper function:

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Manipulating the timezone server-side #

Using date_default_timezone_set() and similar isn’t allowed because it conflicts with stats and other systems. Developers instead should use WordPress’s internal timezone support. More information.

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Removing the admin bar #

The admin bar cannot be removed as it’s integral to the user experience on

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Working with wp_users and user_meta #

As a large multisite install, has a global users database.

Note that this means that you cannot create, edit, or delete users. For greater level of control, use Guest Authors.

This table is huge on and queries on it can easily cause performance issues. This includes doing any JOIN or meta operations against this set of tables. For parsing through a list of users, use get_users() and iterate in PHP.

For storing user additional user metadata, you should look at User Attributes.

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Caching large values in options #

This cache object (and any object in wp_cache in general) must not exceed 1MB. On, options are cached in memory to avoid database lookups, which speed things up. This is only effective if the cached object is kept small. Once the object reaches 1MB, it will no longer cache and requests are sent to the database servers, which, depending on the traffic of the site, can cause a flood of requests and have a severe impact on performance. More information. This 1MB limit is the total limit of all options in the options table. This behaviour is different from the core WordPress implementation, having autoload set to false will not impact this 1MB limitation. One option for getting around this problem is to use the wp_large_options plugin for large option values.

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Skipping Batcache #

Requests that prevent Batcache from caching the page like using $_GET params (e.g. ?abc=def) are not allowed, as they will likely make your site go down. You can use one of the whitelisted params that do not bypass batcache from this list: ‘hpt’, ‘eref’, ‘iref’, ‘fbid’, ‘om_rid’, ‘utm’, ‘utm_source’, ‘utm_content’, ‘utm_medium’, ‘utm_campaign’, ‘utm_term’, ‘utm_affiliate’, ‘utm_subid’, ‘utm_keyword’, ‘fb_xd_bust’, ‘fb_xd_fragment’, ‘npt’, ‘module’, ‘iid’, ‘cid’, ‘icid’, ‘ncid’, ‘snapid’, ‘_’, ‘fb_ref’, ‘fb_source’, ‘_ga’,’hootPostID’ if you want to handle the query data in Javascript. More information.

You should try and implement your URLs using rewrite rules. If you’re having trouble, get in touch and we’ll help 🙂

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Ajax calls on every pageload #

Making calls to admin-ajax.php on every pageload, or on any pageload without user input, will cause performance issues and need to be rethought. If you have questions, we would be happy to help work through an alternate implementation.

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Front-end db writes #

Functions used on the front-end that write to the database are not allowed. This is due to scaling concerns and can easily bring down a site.

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*_meta as a hit counters #

Please don’t use meta (post_meta, comment_meta, etc.) to track counts of things (e.g. votes, pageviews, etc.). First of all, it won’t work properly because of caching and due to race conditions on high volume sites. It’s also just a recipe for disaster and easy way to break your site. In general you should not try to count/track user events within WordPress; consider using a Javascript-based solution paired with a dedicated analytics service (such as Google Analytics) instead.

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eval() and create_function() #

Both these functions can execute arbitrary code that’s constructed at run time, which can be created through difficult-to-follow execution flows. These methods can make your site fragile because unforeseen conditions can cause syntax errors in the executed code, which becomes dynamic. A much better alternative is an Anonymous Function, which is hardcoded into the file and can never change during execution.

If there are no other options than to use this construct, pay special attention not to pass any user provided data into it without properly validating it beforehand.

We strongly recommend using Anonymous Functions, which are much cleaner and more secure.

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switch_to_blog() #

Not something you should ever need to do in a VIP theme context. Use an API (XML-RPC, REST) to interact with other sites if needed.

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get_site_*() #

Not something you should ever need to do in a VIP context. Because is a multisite these are shared between all our sites. this means you cannot use functions like get_site_transient(), set_site_transient() or get_site_option() set_site_option()

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No LIMIT queries #

Using posts_per_page (or numberposts) with the value set to -1 or an unreasonably high number or setting nopaging to true opens up the potential for scaling issues if the query ends up querying thousands of posts.

You should always fetch the lowest number possible that still gives you the number of results you find acceptable. Imagine that your site grows over time to include 10,000 posts. If you specify -1 for posts_per_page, you’ll query with no limit and fetch all 10,000 posts every time the query runs, which is going to destroy your site’s performance. If you know you’ll never have more than 15 posts, then set posts_per_page to 15. If you think you might have more than 15 that you’d want to display but doubt it’d hit more than 100 ever, set the limit to 100. If it gets much higher than that, you might need to rethink the page architecture a bit.

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A bit on Cron-jobs #

Please keep in mind that overly frequent cron events (anything less than 15 minutes) can significantly impact the performance of the site, as can cron events that are expensive. This is because cron-jobs run on the same webservers as the site, and use the same database-servers.

Also, for any cron-jobs that perform sensitive functions (e.g., send emails, alter data in the database), or for jobs that run for more than a minute, we recommend two key actions to be performed. They, in combination, will help getting your cron-job to run smoothly.

First, let us know that you want the cron-job to be executed on our jobs-system. This will not require any change to your code, and only impacts how the cron-jobs are launched. Second, implement locking. The aim of the lock is to make sure no other process is executing the same cron-job simultaneously. The lock is needed, because the WordPress cron-system will schedule a job, even if a previous one is still running, and so two or more can be running at once.

Below there is an example locking-code that you can use, but keep in mind that it will require alterations to fit your theme and the interval your cron-job runs at.

function some_cron_job( ) {
    // Throttle so to guarantee only one process executing this code at once  
    if ( false === get_transient( 'some_cron_job_lock' ) ) {
        // set for 50 minutes
        set_transient( 'some_cron_job_lock', 1, ( 50 * 60 ) );  
    } else { 
        // stop running if locked  

    // Code that should get executed below   
    // .....

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Flash (.swf) files #

Flash (.swf) files are not permitted on as they often present a security threat (largely due to poor development practices or due to bugs in the Flash Player) and vulnerabilities are hard to find/detect/secure. Plus, who needs Flash? 🙂

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Correct licenses #

All plugin and theme code on must be compatible with the GNU Public License v2 (GPL2) license, the same license used for WordPress. Custom code written in-house is fine as long as it complies with the license.

The reasoning for this is that the GPL is the foundation of the WordPress open source project; we want to respect all of the developers who choose to honor this license, and who contribute to the community by building fully GPL compatible themes/plugins.

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Ignore development only files #

If it’s feasible within your development workflow, we ask that you .svnignore any files that are use exclusively in local development of your theme, these include but are not limited to .git, .gitignore, config.rb, sass-cache, grunt files, PHPUnit tests, etc.

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Plugin Registration Hooks #

register_activation_hook() and register_deactivation_hook() are not supported because of the way plugins are loaded on WordPress VIP using wpcom_vip_load_plugin(). Read more here

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VIP Requirements #

Every theme must include a VIP attribution link and wp_head() and wp_footer() calls.

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Unprefixed Functions, Classes, Constants, Slugs #

Long-standing WordPress best practice. Always namespace things in code to avoid potential conflicts. See Prefix Everything.

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Commented out code, Debug code or output #

VIP themes should not contain debug code and should not output debugging information. That includes the use of functions that provide backtrace information, such as “wp_debug_backtrace_summary()” or “debug_backtrace()”. If you’re encountering an issue that can’t be debugged in your development environment, we’ll be glad to help troubleshoot it with you. The use of commented out code should be avoided. Having code that is not ready for production on production is bad practice and could easily lead to mistakes while reviewing (since the commented out code might not have been reviewed and the removing on a comment might slip in accidentally).

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Generating email #

To prevent issues with spam, abuse or other unwanted communications, your code should not generate, or allow users to generate, email messages to site users or user-supplied email addresses beyond the core “subscribe” features offered on That includes mailing list functionality, invitations to view or share content, notifications of site activity, or other messages generated in bulk. Where needed, you can integrate third-party services that allow sharing of content by email, as long as they don’t depend on infrastructure for message delivery.

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Custom wp_mail headers #

The PHP Mailer is properly escaping headers for you only in case you’re using appropriate filters inside WordPress. Every time you want to create custom headers using user supplied data (eg.: “FROM” header), make sure you’re using filters provided by WordPress for you. See and

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Serializing data #

Unserialize has known vulnerability problems with Object Injection. JSON is generally a better approach for serializing data.

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Including files with untrusted paths or filenames #

locate_template(), get_template_part() and sometimes include() or require() are typically used to include templates. If your template name, file name or path contains any non-static data or can be filtered, you must validate it against directory traversal using validate_file() or by detecting the string “..”

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Settings alteration #

Using ini_set() for alternating PHP settings, as well as other functions with ability to change configuration at runtime of your scripts, such as error_reporting(), is prohibited on the VIP platform. Allowed error reporting in production can lead to Full Path Disclosure.

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pre_option_* #

Since the theme is being loaded even in non-standard situations (api, jobs system) you should always check if current blog_id matches the real blog_id of the site running the theme.

Here’s how to do it:

$real_current_blog_id = get_current_blog_id();
//foreach( ... )
add_filter( "pre_option_{$option_name}", function( $value ) use ( $real_current_blog_id, $real_value ) {
    if ( get_current_blog_id() === $real_current_blog_id ) {
        return $real_value;
    } else {
        return $value;

The pre_option_ hooks you should be extra careful with are:

  • pre_option_blogname
  • pre_option_blogurl
  • pre_option_post_count

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Minified Javascript files #

Javascript files that are minified should also be committed with changes to their unminified counterparts.  Minified files cannot be read for review, and are much harder to work with when debugging issues.

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Inserting HTML directly into DOM with Javascript #

To avoid XSS, inserting HTML directly into the document should be avoided.  Instead, DOM nodes should be programmatically created and appended to the DOM.  This means avoiding .html(), .innerHTML(), and other related functions, and instead using .append(), .prepend(),.before(), .after(), and so on.  More information.

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reCaptcha for Share by Email #

To protect against abuse of Jetpack’s share by e-mail feature (aka Sharedaddy) it must be implemented along with reCaptcha. This helps protect against the risk of the network being seen as a source of e-mail spam, which would adversely affect VIP sites. This blog post explains how to implement reCaptcha.

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Querying on meta_value #

WordPress’ postmeta and termmeta tables have an index on meta_key but no index on meta_value. Using WP_Query to perform a meta_value lookup will likely not scale and should be avoided. See Querying on meta_value for more detailed information on how to achieve the desired results.

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flush_rewrite_rules #

Your theme’s rewrite rules are flushed automatically on every deploy (and when you switch themes).
There is no need to ever call flush_rewrite_rules() on WordPress VIP. For more information read our documentation on rewrite rules

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Implicit File Includes #

All files should be included explicitly. For example don’t use glob() or another such function to include all the PHP files in a folder. Patterns such as this:

foreach ( glob( __DIR__ . 'sub_dir/*.php' ) as $file ) {
        require_once( $file );

Make it harder to debug as it’s not explicit when each file is loaded. It also can cause problem with load ordering and might cause unexpected behaviours in the future as some files may be unexpectedly loaded.

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Relative File Includes #

Including files with relative paths may lead to unintended results. All files should be included with an absolute path.

You can use one of the many functions available to compose the file path, such as __DIR__ or dirname( __FILE__ ) or plugin_dir_path( __FILE__ ) or get_template_directory()

// Don't do this:
require_once 'file.php';

// Do this instead:
require_once __DIR__ . '/file.php';

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Error Control Operators #

The at sign (@) used for ignoring any error messages that might be generated by an expression are often hiding bugs and make the debugging hard. Any expression which might generate errors or warnings should be sanitized properly by performing related checks. For instance:

@include( __dir__ . '/file-which-does-not-exist.php' ); //__doing_it_wrong();

if ( true === file_exists( __dir__ . '/file-which-does-not-exist.php' ) ) {
include( __dir__ . '/file-which-does-not-exist.php' );

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Proceed with Caution #

The following approaches should be considered carefully when including them in your VIP theme or plugin.

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Remote calls #

Remote calls such as fetching information from external APIs or resources should rely on the WordPress HTTP API (no cURL) and should be cached. Example of remote calls that should be cached are wp_remote_get(), wp_safe_remote_get() and wp_oembed_get(). More information.

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Using __FILE__ for page registration #

When adding menus or registering your plugins, make sure that you use an unique handle or slug other than __FILE__ to ensure that you are not revealing system paths.

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Functions that use JOINS, taxonomy relation queries, -cat, -tax queries, subselects or API calls #

Close evaluation of the queries is recommended as these can be expensive and lead to performance issues. Queries with known problems when working with large datasets:

  • category__and, tag__and, tax_query with AND
  • category__not_in, tag__not_in, and tax_query with NOT IN (these should never be used unless using Elasticsearch)
  • tax_query with multiple taxonomies

For Taxonomy not in queries the code can be refactored to query more than the wanted amount of posts and then skip the posts in PHP if they have the category assigned to them. You can also often refactor these categories into separate post_types so creating a post_type called breaking_news instead of a category and when appropriate joining both post_types. Elasticsearch can handle these types of query very well and if you have Elasticsearch on your account you can offload it by passing 'es' => true to the query.

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Taxonomy queries that do not specify ‘include_children’ => false #

include_children would previously default to false on but as of 4.4 defaults to true. This means that a previously simple one term query could become a very big query. These queries will often timeout on large datasets. For more information see

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Custom roles #

For best compatibility between environments and for added security, custom user roles and capabilities need to be managed via our helper functions.

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Caching constraints #

As we’re running batcache, server side based client related logic will not work. This includes things like logic based on $_SERVER['REMOTE_ADDR'] or similar. This should be switched to a js based approach or a cookie needs to be set and a batcache exception based on the cookie needs to be made.

Because Batcache caches fully rendered pages, per-user interactions on the server-side can be problematic. This means usage of objects/functions like $_COOKIE, setcookie,$_SERVER['HTTP_USER_AGENT'], and anything that’s unique to an individual user cannot be relied on as the values may be cached and cross-pollution can occur.

In most cases, any user-level interactions should be moved to client-side using javascript. More information.

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Using extract() #

extract() should never be used because it is too opaque and difficult to understand how it will behave under a variety of inputs. It makes it too easy to unknowingly introduce new variables into a function’s scope, potentially leading to unintended and difficult to debug conflicts.

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Inline resources #

Inlining images, scripts or styles has been a common work around for performance problems related to HTTP 1.x As more and more of the web is now served via newer protocols (SPDY, HTTP 2.0) these techniques are now detrimental as they cannot be cached and require to be sent every time with the parent resource. Read more about this here

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Using output buffering #

Output buffering should be used only when truly necessary and should never be used in a context where it is called conditionally or across multiple functions / classes. This sort of behaviour can easily interact with batcache and lead to problems with full page caching. It is also hard to debug and to follow what is happening. If used it should always be in the same scope and not with conditionals.

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Using $_REQUEST #

$_REQUEST should never be used because it is hard to track where the data is coming from (was it POST, or GET, or a cookie?), which makes reviewing the code more difficult. Additionally, it makes it easy to introduce sneaky and hard to find bugs, as any of the aforementioned locations can supply the data, which is hard to predict. Much better to be explicit and use either $_POST or $_GET instead.

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Using == instead of === #

PHP handles type juggling. Meaning that this:

$var = 0;
if ( $var == 'safe_string' ){
    return true;

Will return true. Unless this is the behavior you want you should always use === over ==.
Other interesting things that are equal are:

  • (bool) true == ‘string’
  • null == 0
  • 0 == ‘0SQLinjection’
  • 1 == ‘1XSS’
  • 0123 == 83 (here 0123 is parsed as an octal representation)
  • 0xF == 15 (here 0xF is parsed as an hexadecimal representation of a number)
  • 01 == ‘1string’
  • 0 == ‘test’
  • 0 == ”

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Using in_array() without strict parameter #

PHP handles type juggling. This also applies to in_array() meaning that this:

in_array( 0, ['safe_value', 'another string']);

Will return true. Unless this is the behavior you want you should always set the strict parameter to true. See Using == instead of ===

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Check for is_array(), !empty() or is_wp_error() #

Before using a function that depends on an array, always check to make sure the arguments you are passing are arrays. If not PHP will throw a warning.

For example instead of

$tags = wp_list_pluck( get_the_terms( get_the_ID(), 'post_tag') , 'name');


$tags_array = get_the_terms( get_the_ID(), 'post_tag');
//get_the_terms function returns array of term objects on success, false if there are no terms or the post does not exist, WP_Error on failure. Thus is_array is what we have to check against
if ( is_array( $tags_array ) ) {
    $tags = wp_list_pluck( $tags_array , 'name');

Here are some common functions / language constructs that are used without checking the parameters before hand:
foreach() array_merge(), array_filter(), array_map(), array_unique(), wp_list_pluck()
Always check the values passed as parameters or cast the value as an array before using them.

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Not Using the Settings API #

Instead of handling the output of settings pages and storage yourself, use the WordPress Settings API as it handles a lot of the heavy lifting for you including added security.

Make sure to also validate and sanitize submitted values from users using the sanitize callback in the register_setting call.

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Using Page Templates instead of Rewrites #

A common “hack” in the WordPress community when requiring a custom feature to live at a vanity URL (e.g. /lifestream/) is to use a Page + Page Template. This isn’t ideal for numerous reasons:

  • Requires WordPress to do multiple queries to handle the lookup for the Page and any additional loops your manually run through.
  • Impedes development workflow as it requires the Page to be manually created in each environment and new developer machines as well.

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Not defining post_status Or post_type #

By default the post_status of a query is set to publish for anonymous users on the front end. It is not set in any WP_ADMIN context including Ajax queries. Queries on the front end for logged in users will also contain an OR statement for private posts created by the logged in user, even if that user is not part of the site. This will reduce the effectiveness of MySQL indexes, specifically the type_status_date index.

The same is true for post_type, if you know that only a certain post_type will match the rest of the query (for example for a taxonomy, meta or just general query) adding the post_type as well as the post_status will help MySQL better utilize the indexes as it’s disposal.

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Use wp_json_encode() over json_encode() #

wp_json_encode() will take care of making sure the string is valid utf-8 while the regular function will return false if it encounters invalid utf-8. It also supports backwards compatibility for versions of PHP that do not accept all the parameters.

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Using closing PHP tags #

All PHP files should omit the closing PHP tag to prevent accidental output of whitespace and other characters, which can cause issues such as ‘Headers already sent‘ errors. This is part of the WordPress Coding Standards.

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Use wp_safe_redirect() instead of wp_redirect() #

Using wp_safe_redirect(), along with the allowed_redirect_hosts filter, can help avoid any chances of malicious redirects within code.  It’s also important to remember to call exit() after a redirect so that no other unwanted code is executed.

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Mobile Detection #

When targeting mobile visitors, jetpack_is_mobile() should be used instead of wp_is_mobile.  It is more robust and works better with full page caching.

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Using bloginfo() without escaping #

Keeping with the theme of Escaping All the Things, code that uses bloginfo() should use get_bloginfo() instead so that the data can be properly late escaped on output.  Since get_bloginfo() can return multiple types of data, and it can be used in multiple places, it may need escaped with many different functions depending on the context:

echo '<a href="' . esc_url( get_bloginfo( 'url' ) ) . '">' . esc_html( get_bloginfo( 'name' ) ) . '</a>';

echo '<meta property="og:description" content="' . esc_attr( get_bloginfo( 'description' ) ) . '">';

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Missing X-Frame-Options Headers #

Clickjacking is a type of vulnerability that allows an attacker to ‘hijack’ the click of an unsuspecting user, tricking them into clicking on a different element on a different site, via carefully positioned iframes and page elements.

To prevent this, sites can send the X-Frame-Options header to control how the site may be iframed. This is especially important on any site that has an authenticated experience on the frontend.

The admin and login areas of WP already send the X-Frame-Options: DENY header to prevent clickjacking.

More info on Clickjacking can be found at OWASP, and more information about X-Frame-Options can be found at MDN.

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Performance Considerations #

We want to make sure that your site runs smoothly and can handle any traffic load. As such, we check your site for performance considerations such as: are remote requests fast and cached? Does the site request more data than needed?

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Uncached Pageload #

Uncached pageloads should be optimized as much as possible. We will load different pages and templates on your theme uncached, looking for slow queries, slow or timed out remote requests, queries that are overly repeated, or function routines that are slow.

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Memcache hits/misses #

Memcache misses or over-additions/updates can be a sign of potential problems.

    • Clear your cache on a page
    • In the “Memcache” tab in the Debug Bar, check the ratio of sets/adds vs gets. You should see almost as many sets/adds as gets.
    • Reload the page (without clearing the cache)
    • In the “Memcache” tab in the Debug Bar, check the ratio of sets/adds vs gets. You should see (almost) no sets/adds.
    • Reload the page a few more times and check the set/add-to-get ratio; the former should continue to remain 0 or minimal.

If you’re still seeing sets/adds in subsequent pages, that means that something is constantly being added to the cache that shouldn’t.

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