Pattern

Regex for JWT token

JSON Web Token — three base64url segments.

The JWT token regex is ^[A-Za-z0-9_-]+\.[A-Za-z0-9_-]+\.[A-Za-z0-9_-]*$ — copy it below, or open it in the explainer for a token-by-token breakdown.

The pattern

^[A-Za-z0-9_-]+\.[A-Za-z0-9_-]+\.[A-Za-z0-9_-]*$

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What it matches

eyJhbGciOiJIUzI1NiJ9.eyJzdWIiOiIxMjMifQ.SflKxwRJSMeKKF2QT4fwpMeJf36POk6yJV_adQssw5c

What it doesn't match

not.a.jwt.invalid
onlyone.segment
two.segments

Notes & gotchas

Three segments separated by dots. Each uses base64url alphabet (no padding, - and _ instead of + and /). The third segment can be empty for unsigned tokens. Doesn't verify the signature.

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)
`[A-Za-z0-9_-]+`	one or more: any of: uppercase letters, lowercase letters, digits, “_”, “-”
`\.`	literal “.”
`[A-Za-z0-9_-]+`	one or more: any of: uppercase letters, lowercase letters, digits, “_”, “-”
`\.`	literal “.”
`[A-Za-z0-9_-]*`	zero or more: any of: uppercase letters, lowercase letters, digits, “_”, “-”
`$`	end of string (or line in multiline mode)

About this pattern

Identifier formats like UUIDs, hashes, and version strings have well-defined structures that regex captures cleanly. The pattern verifies format; checksums and validity against a registry need additional checks.

Quick usage in different languages

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

JavaScript: /^[A-Za-z0-9_-]+\.[A-Za-z0-9_-]+\.[A-Za-z0-9_-]*$/.test(value)
Python: re.match(r"^[A-Za-z0-9_-]+\.[A-Za-z0-9_-]+\.[A-Za-z0-9_-]*$", value)
Java: Pattern.compile("^[A-Za-z0-9_-]+\\.[A-Za-z0-9_-]+\\.[A-Za-z0-9_-]*$").matcher(value).matches()
C# / .NET: Regex.IsMatch(value, @"^[A-Za-z0-9_-]+\.[A-Za-z0-9_-]+\.[A-Za-z0-9_-]*$")
Go: regexp.MustCompile(`^[A-Za-z0-9_-]+\.[A-Za-z0-9_-]+\.[A-Za-z0-9_-]*$`).MatchString(value)
Ruby: /^[A-Za-z0-9_-]+\.[A-Za-z0-9_-]+\.[A-Za-z0-9_-]*$/.match?(value)
PHP: preg_match('~^[A-Za-z0-9_-]+\.[A-Za-z0-9_-]+\.[A-Za-z0-9_-]*$~', $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.
ASCII letters only. [a-zA-Z] excludes accented and non-Latin letters (é, ü, ß, ñ, and non-Latin scripts). For international input use Unicode properties like \p{L} with the u 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 jwt token 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.

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