Detect internationalized domain name (IDN) homograph attacks using confusable Unicode characters that mimic ASCII domains.
IDN Homograph Attack Detector examines a domain name for Unicode characters that can be mistaken for ordinary ASCII letters or digits. It checks character identities instead of trusting how the hostname looks on screen, calling attention to substitutions that can make a phishing domain resemble a familiar name. The key surprise is that visual similarity does not mean textual equality: two labels may look nearly identical while containing different Unicode code points and naming entirely separate domains. Its result is a spelling-risk signal, not proof that a domain is malicious.
The detector examines the code points in each domain label and looks for non-ASCII characters that resemble familiar ASCII characters. A Cyrillic or Greek letter, for example, can appear close to a Latin letter in some fonts while remaining a different character. Identifying that distinction helps expose hostnames designed to survive a quick visual inspection.
Internationalized labels can appear as readable Unicode or in an ASCII-compatible form whose label begins with xn--. Homograph analysis concerns the Unicode characters represented by that label, because those are the characters a browser may show to a reader. Each dot-separated label must be considered independently; an ordinary suffix does not make a deceptive preceding label trustworthy.
No. The xn-- prefix marks an ASCII-compatible representation of an internationalized domain label, and many legitimate domains use it to support non-ASCII writing systems. Concern arises when the represented Unicode characters create a misleading resemblance or other suspicious spelling. Registration context and the independently verified official domain still matter.
No. It can identify character-level features associated with IDN homograph attacks, but those features do not establish ownership, activity, or intent. Confirm the expected domain through a trusted source and investigate registration, hosting, certificates, redirects, and observed content separately. Avoid visiting a suspicious hostname merely to validate the detector's warning.
The behavioral notes were checked against the browser implementation. Standards and primary references below define the relevant format, formula, or platform behavior.
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