Citadel is built on state of the art technology

When we set out to build Citadel, we had simple parameters. It had to block what it's told to block, it can't block things it shouldn't, and it needed to be a hands-off experience because frankly, filters that put you to work are just making you do a job they can't.

As simple as these parameters are, they demand a great deal in the way of technology. We knew that the only way to truly hit this mark was to reach to the very limits of what we know can be done, and then push that line a little further.

We have packed Citadel with technology refined over years of research and developement. Below, we cover how each of those technologies is put to work for you.

A trial is worth a thousand words

You can run a free, no-commitment trial of Citadel without even having to register an account. Limited to a single trial per device.

Image Filtering
Citadel has learned to see so you don't have to

Citadel's image filter uses state-of-the-art neural networks to scan images before they reach your browser and determine if they contain adult content.

Citadel is able to obtain, in our own internal testing, a staggering 98.18% overall accuracy at classifying images.

Citadel scans every single compatible image coming across your network at blistering speeds. On a modern computer, Citadel can classify approximately 175 images per second. That's fast enough to classify every frame of 7 cinematic videos simultaneously, in real-time.

Adult Image Detection Accuracy
Adult Art Detection Accuracy
Provocative Imagery Detection Accuracy
Neutral Content Detection Accuracy
Overall Accuracy
Video Filtering
Citadel watches videos just moments ahead of you in time

Relying partly on the image filtering technology, Citadel is able to watch video as it is streamed to your browser just moments ahead of you in time. When Citadel detects any adult content in the video stream, the stream is abruptly terminated.

This technology is the latest addition to Citadel. We wish we could tell this works on every video stream, but it simply cannot. Video content is a patent minefield and the number of video formats being used is mind-boggling. It's not possible to ever cover them all, though we always strive to improve all of Citadel's systems in our continuous development.

Fortunately, many of the biggest providers of streamed video typically ship content we can inspect and for every compatible video format that Citadel enounters, Citadel will observe videos in real time just ahead of your point in the stream and terminate it immediately should it see something untoward.

This component is designed to work in tandem with Citadel's other components as an additional layer of security. When video streams are terminated due to the detection of adult content, it's entirely possible for at least a few bad frames to make it to your screen before the stream is killed, due to the complex asynchronous and parallel nature of network communications.

Citadel's video filter is a "last line of defense" in the event that raw video is somehow being obtained from a source that has no text content to classify and originating from a seemingly innocuous link.

Examples of this include content posted on social media that violate community standards, but have not yet been removed. The site itself may be perfectly innocent, but some nefarious person has uploaded a video of adult content, with no description, and the only way for a filter to know this is to actually watch the video.

Where other filters would be entirely unable to detect such a scenario, Citadel could, and though a few frames might make it to the screen before Citadel is able to terminate it, the rest of the video would fail to play, greatly mitigating the intrusion by the unwanted content. It is recommended to use the video filter in conjunction with all other forms of filtering for maximum protection.

Text Filtering
Citadel can read

44 Languages

Citadel can read in 44 languages.


141 Categories

While reading, Citadel can classify what it's seeing into 141 categories, in all 44 languages.


Compositional Classification

Citadel doesn't make a binary choice when classifying text. Instead, it will identify all topics in the text and rate their importance individually.


Keyphrase Filter

In addition, Citadel can also rapidly identify keywords or key phrases in text content.

We trained Citadel's text subsystem on more text and in more languages than a human could hope to read in a lifetime. Using another form of machine learning, Citadel is able to identify the language of text that it sees and, if the language is one of the 44 that Citadel knows, it will perform a compositional classification of the text.

What is "compositional" classification?

This is crucial because it's how we humans understand things. Typical text classification technology is trained to identify the most prevelant topic in text. Imagine reading a whole page out of any book and being told you can only pick one word to describe what you just saw. Common sense tells you that would be very inaccurate. We all know the page could be equally about any number of topics. Or, perhaps there's one topic that, while briefly mentioned, is powerfully stated and therefore highly relevant.

Simply put, Citadel reads like you do, not like a bad robot.

What is keyword/keyphrase filtering?

You can configure lists in Citadel that identify keywords or keyphrases in text and block the content when they're found. This supplementary subsystem is separate from the A.I. driven classification described above, but still part of overall text filtering.

Additionally, keywords and keyphrases are not just applied to web content, but web addresses as well, so you don't need to duplicate these rules into separate URL rules. This is done automatically.

Chat Filtering
Citadel recognizes sexually suggestive and explicit chat messages and alerts you

Citadel is trained to analyze compatible chat messages to determine if they contain sexually suggestive or explicit language. Chat messages that are deemed to be sexually suggestive or explicit are automatically logged and, based on your preference, permitted or blocked entirely when this subsystem is enabled.

This is a subsystem that strikes a balance between privacy and protection. We don't want to create tools that force you to conduct total surveillance, which sadly has become the norm in this industry. Rather, we'd simply like to log events that may require your attention in this case and give you the option to block them entirely.

We believe that the trend toward total surveillance is a result of laziness or ineptitude on the part of other companies, being incapable or unwilling to make scientific advances in content classification. With Citadel, there's no rift or implicit distrust between parent and child or employer and employee. A neutral, unbiased machine is observing and only making things known that it believes pose a potential risk, permitting privacy everywhere else.

This system is enabled by default and operates in all 44 languages that Citadel knows.

URL Filtering
Citadel powerfully reinvents this time-tested technology

Website Blocking

Block rules are second only to exemption rules and override all of Citadel's technology stack and simply never let anything from a matching website through.


Powerful Filter Syntax

Citadel implements an extremely fast regular-expression-style URL filtering syntax. Want to see example.com but not load any images? Perfect, ||example.com$image will do it.


Website Exempting

Exemption rules preceed and override all of Citadel's technology stack, letting anything from a matching website through without inspection.

With Citadel's various A.I. systems for classification, this feature would have been redundant to include if not for the powerful syntax packed into it.

With this system, as you probably know, you can always just punch in example.com to an allow list or block list and be done with it. You can even plug in mint and block any URL that has "mint" in it.

But what if you think "mint" is fine, so long as it's not added to chocolate? Well, with Citadel's powerful syntax, you use a chocolate*mint rule to block any URL that has the word mint anywhere after the word chocolate. Of course we know this is an outlandish example, nobody hates mint chocolate, but you get the idea.

On a more practical note, if you're interested in using this feature, you don't need to become a wizard in this mini-filter language. There are a multitude of open source lists* containing rules for many different purposes such as blocking ads, blocking trackers for the sake of privacy, etc, that can be dropped right into Citadel. The best part is, with Citadel for PC, these rules get applied to every single application, not just your web browser.

*We're not affiliated with, nor responsible for, any external resource we link to, nor do we endorse the use of or warranty anything third-party.
Keyword Censor
Citadel can "bleep" out the words you don't want to see

Based on the keyword/keyphrase subsystem described in the text filtering section, Citadel can take the action of replacing keywords or keyphrases with asterisks, rather than blocking the resource entirely.

Citadel ships with a "bad word" list built-in and enabled by default, and this is the subsystem that powers it. You can edit this list or add your own lists.

Dark Web Neutralization


Dark Web Disabled

Citadel completely disables the Dark Web at Ring-0, which is the inner-most core of the operating system.


Proxy Protocols Forbidden

Citadel completely disables network protocols that are used to hide traffic you want to filter.


Nowhere To Hide

Citadel will find traffic trying to hide by using alternate ports and terminate those connections.

In our view, a content filter is useless if it can be trivially bypassed. Did you know, that the TOR browser* can easily defeat most content filters? We can assure you that people who want to bypass content filters know this.

These kinds of bypasses are downplayed or not discussed much and for good reason: imagine an industry where "trusted" names sell you assurances that can evaporate with the click of a button, or by copy and pasting a simple command.

This is why Citadel has a custom network driver we've built in-house. This driver lives in the heart of your operating system, well beyond even user privilege. It's within this highly protected sphere that we deploy complex network code that does real-time analysis on absolutely every connection your computer makes, specifically to detect the things we've detailed above.

Because of this design, you can rest assured that your rules are not being trivially thwarted.

App Internet Control

Citadel also enables you to choose which software to filter, which software to exempt from filter, as well as deny specific software access to websites, effectively cutting that software off from having any website access while leaving other apps uninterrupted.

*We're not affiliated with, nor responsible for, any external resource we link to, nor do we endorse the use of or warranty anything third-party.
Power & Performance
Citadel's core technology is engineered in-house for maximum speed and accuracy

Citadel's driver does not degrade down-stream network performance at all. In our internal testing on gigabit internet, Citadel's highly optimized driver causes no impact on downstream transfer speed.

Aside from the driver, Citadel's other technologies are engineered with the same goals in mind. We aim for the highest achievable accuracy and then optimize to provide you with state-of-the-art functionality that enhances your experience, rather than detract from it.

On Device Filtering

Citadel also operates entirely on your device. Some content filters use data centers and server clusters to provide you services. This means your private data is going out into the hands of a third-party which greatly increases the attack surface that could potentially cause you harm.

In addition to this, these data centers and server clusters come at extreme cost, financially and otherwise. They are a massive draw on the electrical grid and generate extreme heat. The cost is passed on to you.

Since Citadel does all of it's work on your device, there is no increased risk to your privacy, nor is the power grid being unecessarily taxed on your behalf.