The Detector404 website does not draw independent conclusions about the presence of failures; it only collects and analyzes publicly available information — user complaints and network telemetry. The information posted on Detector404 is not an official confirmation of a malfunction (defect, damage, failure, outage).

The «Analytics» tool of the Detector404 website includes:

• A database of historical data on the quality of operation of web resources (popular and well-known companies) covering a period of 1 year;
• Tools for visualizing historical data in the form of graphs.

In other words, the user is provided with an interactive chart where they can independently select applications, websites, and a time interval, as well as cities and providers, to create a graph of service quality.

If you have an account, you can compare the operational quality of your website with that of a competitor's website using the «Analytics» tool.

Visit Detector404 and click on the "tile" of your website, or enter its name/address into the search field and select one of the suggested options.

You will be redirected to the website page, where the current status of accessibility and user complaints about its operation will be displayed.

If you have an account, you have access to three notification technologies:

• Notification via Telegram bot;
• Email notifications;
• API integration.

Notification settings, including thresholds, filters, and blacklists, are accessible in your profile on the website.

Response time of a resource is the duration required to send a request and receive the initial meaningful data from the queried resource.

Each resource has its own digital footprint — including header sizes and contents, content type, connection protocol, and other factors — all of which influence delay measurement. For example, the response time of a simple business card website will be significantly less than that of a complex online store, which additionally requires redirection to a regional mirror and passes through complex JavaScript checks and protections.

The response time itself is not an indicator of a service failure; however, a sudden change in it may indicate potential issues.

A resource is considered unavailable over the network if three out of five consecutive connection attempts to the resource fail from different cities.

Connection attempts are considered unsuccessful if:

• HTTP response code is 4XX or 5XX;
• Response not received within 15 seconds;
• Connection error occur, for example, due to DNS issues.

A fault is a general term that refers to the loss of operability, i.e., a violation of the acceptable thresholds of the main parameters of IT operation.

Faults can be classified into four types:

• Defect (bug, problem) — a flaw in an IT component that can lead to a failure or outage. For example, software released without proper quality checks of the code;
• Damage — an event resulting in a violation of the integrity of an object while its operability is preserved. For example, an attack that disables an IT system;
• Failure — a disruption of operability that is resolved by operator intervention. For example, CPU load on a firewall increases, and a reboot resolves the issue;
• Outage — the main parameters of an IT system's operation do not show anomalies, but the system is not fully functional. For example, a bank's website operates, but the function to view transaction history is inaccessible in the personal account.

In colloquial speech, a single term — "failure" — is often used to refer to various issues, such as "network failure," "logical failure," "hardware failure," "software failure," etc.

Our geographically distributed monitoring servers (crawlers) perform the following checks on websites:

• HTTP/HTTPS page load codes.
  Connects to the website and records the obtained HTTP code. If the code is "200 OK" — the page loaded successfully; if "500 Internal Server Error" — an internal server error; if "404 Not Found" — the page was not found.
• Availability via ICMP protocol (PING).
  Must have;
• Correct DNS resolution of the domain name to an IP address.
  We check whether the domain example.com correctly resolves to an IP address via DNS servers. An incorrect DNS-to-IP conversion can cause resource inaccessibility;
• Checks of TCP port accessibility.
  Connect to TCP ports 80, 443, and others (upon request) and verify that TCP sessions are established;
• SSL certificate validity.
  Checks include: validity of the certificate, expiration date, domain name matching the certificate, and the trust chain;
• Domain name registration period checks.
  We verify the registration expiry date of site domain name and notify if the registration period is nearing its end.

The primary notification method is a public Telegram channel, where outage messages are posted with a 5-minute delay.

If you have an account, you can customize notification settings — such as companies, brands, URLs, thresholds, etc. — and use the following:

• Notification via Telegram bot;
• Email notifications;
• API integration.

• LLM-based classification of complaint text (hidden advertising, aggression, flash mobs, political statements, etc.)
• Attribution of complaints using GeoIP databases + browser User-Agent + TLS JA3/JA4, etc.
• Session management, for example, HTTP cookies, etc.

We do not disclose the operating principles of each anti-fraud mechanism.

We do not ask users to provide personal data in complaints and comments. For the purposes of the project — identifying outages and building statistics — we do not need full names, phone numbers, addresses, passport data, banking details, or other information that can identify a user.

At the same time, technical data, cookie identifiers, information about the device, browser, and actions on the site may be processed for the operation of the website.

Such processing is carried out in accordance with the Privacy Policy.

Public outage statistics are generated on the basis of anonymized or aggregated data. If a user independently posts personal data in the text of a complaint or comment, we take measures to detect, mask, or remove it.