Regex for YAML key
YAML key — alphanumeric and dashes followed by colon.
The YAML key regex is ^([a-zA-Z_][\w-]*)\s*: — copy it below, or open it in the explainer for a token-by-token breakdown.
The pattern
^([a-zA-Z_][\w-]*)\s*:
What it matches
name:first_name:app-version:env :
What it doesn't match
indented:123key:-list_item
Notes & gotchas
Matches a top-level YAML key. Uses /m flag for multiline. Doesn't handle quoted keys, flow-style mappings, or deeply nested keys — use a YAML parser for those.
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.
Open in explainer →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 |
[a-zA-Z_] | any of: lowercase letters, uppercase letters, “_” |
[\w-]* | zero or more: any of: word chars (A–Z, a–z, 0–9, _), “-” |
) | end of group |
\s* | zero or more: whitespace |
: | literal text “:” |
About this pattern
Developer-oriented patterns help with code analysis, log parsing, and data transformation. Use these in build scripts, CI tools, IDE search-and-replace, and code review utilities.
Quick usage in different languages
This exact pattern — with the correct escaping and idioms for each language:
- JavaScript:
/^([a-zA-Z_][\w-]*)\s*:/.test(value) - Python:
re.match(r"^([a-zA-Z_][\w-]*)\s*:", value) - Java:
Pattern.compile("^([a-zA-Z_][\\w-]*)\\s*:").matcher(value).matches() - C# / .NET:
Regex.IsMatch(value, @"^([a-zA-Z_][\w-]*)\s*:") - Go:
regexp.MustCompile(`^([a-zA-Z_][\w-]*)\s*:`).MatchString(value) - Ruby:
/^([a-zA-Z_][\w-]*)\s*:/.match?(value) - PHP:
preg_match('~^([a-zA-Z_][\w-]*)\s*:~', $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 ^, 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 yaml key against a source of truth (database, API, or checksum) where it matters.
Related patterns
More patterns in the Developer category:
See also
Browse all 300 patterns in the library, or open this regex in the interactive explainer to see a token-by-token breakdown, test against custom input, and generate code in seven languages.