Pattern

Regex for Hong Kong HKID

Hong Kong identity card — 1-2 letters + 6 digits + check.

The pattern

^[A-Z]{1,2}\d{6}$[\dA]$$

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What it matches

A123456(7)
AB123456(A)
Z999999(0)

What it doesn't match

A1234567
A123456-7
a123456(7)

Notes & gotchas

HKID format: 1-2 letters + 6 digits + check digit in parentheses (digit 0-9 or A for value 10). Letters before 1949 use 1 char, after use 2. Check char from modulus-11 algorithm.

Code in your language

Use the explainer's Code tab to generate ready-to-paste snippets in JavaScript, Python, Java, .NET, Go, Ruby, and PHP for this pattern.

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About this pattern

Country-specific identifier formats vary widely. The pattern below validates structure; many real IDs include checksums that regex can't verify. For high-stakes use, validate against the issuing authority.

Quick usage in different languages

Once you've validated a candidate value matches this pattern, you'll typically use it inside your application code. Each language has its own regex syntax:

JavaScript: new RegExp(pattern).test(value) or /pattern/.test(value)
Python: re.match(pattern, value) with raw strings: r"pattern"
Java: Pattern.compile(pattern).matcher(value).matches()
C# / .NET: Regex.IsMatch(value, pattern)
Go: regexp.MustCompile(pattern).MatchString(value) — Go uses RE2 so some advanced features aren't available
Ruby: value =~ /pattern/ or pattern.match?(value)
PHP: preg_match('/pattern/', $value)

The explainer's Code tab generates these for any pattern you paste — including the right escaping and idioms for each language.

Common pitfalls

Anchors matter. The pattern starts with ^ and ends with $ — it expects the entire input to match. To find this pattern inside a longer text, remove the anchors and use the /g flag for multiple matches.
Case sensitivity. Letter ranges like [A-Z] only match uppercase. Use the i flag or [A-Za-z] for case-insensitive matching.
Escape user input. If you're building a regex from a string variable, escape regex metacharacters first to avoid bugs or injection — use RegExp.escape-equivalents in your language.
Performance. For this specific pattern the risk is low, but be cautious of nested quantifiers when adapting it — they can cause exponential backtracking on adversarial input.