Pattern

Regex for Port number

TCP/UDP port — 0 to 65535.

The Port number regex is ^(6553[0-5]|655[0-2]\d|65[0-4]\d{2}|6[0-4]\d{3}|[1-5]\d{4}|[1-9]\d{0,3}|0)$ — copy it below, or open it in the explainer for a token-by-token breakdown.

The pattern

^(6553[0-5]|655[0-2]\d|65[0-4]\d{2}|6[0-4]\d{3}|[1-5]\d{4}|[1-9]\d{0,3}|0)$

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What it matches

0
80
443
8080
65535

What it doesn't match

65536
-1
99999
abc

Notes & gotchas

Strict range 0–65535. For loose validation, ^\d{1,5}$ works but accepts invalid ranges.

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)
`(`	start of a capturing group
`6553`	literal text “6553”
`[0-5]`	any of: 0–5
`\|`	OR — try the alternative
`655`	literal text “655”
`[0-2]`	any of: 0–2
`\d`	any digit (0–9)
`\|`	OR — try the alternative
`65`	literal text “65”
`[0-4]`	any of: 0–4
`\d{2}`	exactly 2 times: digit (0–9)
`\|`	OR — try the alternative
`6`	literal text “6”
`[0-4]`	any of: 0–4
`\d{3}`	exactly 3 times: digit (0–9)
`\|`	OR — try the alternative
`[1-5]`	any of: 1–5
`\d{4}`	exactly 4 times: digit (0–9)
`\|`	OR — try the alternative
`[1-9]`	any of: 1–9
`\d{0,3}`	between 0 and 3 times: digit (0–9)
`\|`	OR — try the alternative
`0`	literal text “0”
`)`	end of group
`$`	end of string (or line in multiline mode)

About this pattern

Developer-oriented patterns help with code analysis, log parsing, and data transformation. Use these in build scripts, CI tools, and code review utilities.

Quick usage in different languages

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

JavaScript: /^(6553[0-5]|655[0-2]\d|65[0-4]\d{2}|6[0-4]\d{3}|[1-5]\d{4}|[1-9]\d{0,3}|0)$/.test(value)
Python: re.match(r"^(6553[0-5]|655[0-2]\d|65[0-4]\d{2}|6[0-4]\d{3}|[1-5]\d{4}|[1-9]\d{0,3}|0)$", value)
Java: Pattern.compile("^(6553[0-5]|655[0-2]\\d|65[0-4]\\d{2}|6[0-4]\\d{3}|[1-5]\\d{4}|[1-9]\\d{0,3}|0)$").matcher(value).matches()
C# / .NET: Regex.IsMatch(value, @"^(6553[0-5]|655[0-2]\d|65[0-4]\d{2}|6[0-4]\d{3}|[1-5]\d{4}|[1-9]\d{0,3}|0)$")
Go: regexp.MustCompile(`^(6553[0-5]|655[0-2]\d|65[0-4]\d{2}|6[0-4]\d{3}|[1-5]\d{4}|[1-9]\d{0,3}|0)$`).MatchString(value)
Ruby: /^(6553[0-5]|655[0-2]\d|65[0-4]\d{2}|6[0-4]\d{3}|[1-5]\d{4}|[1-9]\d{0,3}|0)$/.match?(value)
PHP: preg_match('~^(6553[0-5]|655[0-2]\d|65[0-4]\d{2}|6[0-4]\d{3}|[1-5]\d{4}|[1-9]\d{0,3}|0)$~', $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.
Escape it correctly per language. In Java and JavaScript strings each backslash must be doubled (\\d); in Python, Go, and C# use raw/verbatim strings so the backslashes survive.
Validate beyond format. Matching the format doesn't guarantee the value is real. Confirm the port number 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.

RFC 6335 — IANA Service Name and Port Number Procedures

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