Pattern

Regex for Hex number with 0x prefix

C/JS style hex literal: 0xABC123.

The Hex number with 0x prefix regex is ^0[xX][0-9a-fA-F]+$ — copy it below, or open it in the explainer for a token-by-token breakdown.

The pattern

^0[xX][0-9a-fA-F]+$

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What it matches

0x1A
0xDEADBEEF
0X42
0xff

What it doesn't match

1A
0xGHI
0x

Notes & gotchas

Hex literal as used in C, JavaScript, Python. Must have at least one hex digit after the 0x/0X prefix.

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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Token-by-token breakdown

Every part of the pattern, left to right:

Token	Meaning
`^`	start of string (or line in multiline mode)
`0`	literal text “0”
`[xX]`	any of: “x”, “X”
`[0-9a-fA-F]+`	one or more: any of: digits, a–f, A–F
`$`	end of string (or line in multiline mode)

About this pattern

Number patterns appear constantly in form validation, log parsing, and data extraction. Regex is great for matching the shape but limited for semantic checks (range validation, mathematical constraints).

Quick usage in different languages

This exact pattern — with the correct escaping and idioms for each language:

JavaScript: /^0[xX][0-9a-fA-F]+$/.test(value)
Python: re.match(r"^0[xX][0-9a-fA-F]+$", value)
Java: Pattern.compile("^0[xX][0-9a-fA-F]+$").matcher(value).matches()
C# / .NET: Regex.IsMatch(value, @"^0[xX][0-9a-fA-F]+$")
Go: regexp.MustCompile(`^0[xX][0-9a-fA-F]+$`).MatchString(value)
Ruby: /^0[xX][0-9a-fA-F]+$/.match?(value)
PHP: preg_match('~^0[xX][0-9a-fA-F]+$~', $value)

The explainer’s Code tab regenerates these for any pattern you paste, and the downloadable cheat sheet bundles the breakdown, all seven snippets, and the pitfalls below onto one printable page.

Common pitfalls

Anchored to the whole string. This pattern uses ^ and $, so it requires the entire input to match. To find it inside a longer text, drop the anchors and use the global (g) flag.
Case sensitivity. Letter ranges are case-sensitive — use the i flag if the input case can vary.
Validate beyond format. Matching the format doesn't guarantee the value is real. Confirm the hex number with 0x prefix against a source of truth (database, API, or checksum) where it matters.

Standards & sources

This pattern is based on the following authoritative specification(s) and issuing authorities. Formats can change — always confirm against the primary source.

W3C CSS Color Module Level 4

Related patterns

More patterns in the Numbers & text category: