Regex → tree + per-node description

When to use it

Unfolding someone else's regex to understand the meaning quickly, verifying that your pattern actually has the structure you intended, or learning regex by visually checking precedence among quantifiers, groups, and alternation.

Input → AST tree

Paste a regex (with optional flags) and it expands into an AST tree. Indentation and box-drawing characters (├ └ │) show parent-child relations, with English narrative alongside.

SEQUENCE
├─ ANCHOR ^                 — start of line / input
├─ GROUP #1
│  └─ QUANTIFIER {3}        — repeats exactly 3 times (greedy)
│     └─ ESCAPE \d          — a digit (0–9)
├─ LITERAL "-"              — the character "-"
├─ GROUP #2
│  └─ QUANTIFIER {2}        — repeats exactly 2 times (greedy)
│     └─ ESCAPE \d
├─ LITERAL "-"
├─ GROUP #3
│  └─ QUANTIFIER {4}
│     └─ ESCAPE \d
└─ ANCHOR $                 — end of line / input

How it differs from regex-tester

| Tool | Question it answers | |---|---| | regex-tester | "Where does this pattern match?" — compares text against the pattern, extracts matches and captures. | | regex-visualizer | "What does this pattern mean?" — unfolds the structure of the pattern itself. |

Debug flow: ambiguous pattern → visualize to confirm intent → send to tester to verify matches. The "→ Send to regex tester" button at the top right hands the pattern and flags off directly.

Supported syntax

• Sequence
• Alternation |
• Capturing () and non-capturing (?:) groups
• Character classes [...], negated [^...]
• Every escape (\d \D \w \W \s \S \b \B \n \t \r \f \v \0 plus arbitrary character escapes like \., \+, \()
• Anchors ^ $
• . (any single character)
• Quantifiers * + ? {n} {n,} {n,m} (both greedy and lazy ?)

Not supported (V1)

These are preserved as UNSUPPORTED nodes — flagged red in the tree:

• Lookahead (?=), lookbehind (?<=), negative (?!) (?<!)
• Named groups (?<name>)
• Backreferences \1, \k<name>
• Inline flags (?i)

Candidates for V2 deeper expansion. Surrounding structure parses correctly even when an unsupported pattern is present — you'll see exactly which part is unsupported.

Privacy

Internal-system validation regexes, unpublished pattern libraries, and patterns you're debugging are not transmitted. The AST parser is built in — zero external libraries, zero external calls.

Not the right tool when

• Railroad SVG diagram — V1 is a text tree only. Railroad SVG involves heavy layout math; it's a V2 deeper expansion.
• PCRE / Python re engines — JavaScript regex is the baseline. PCRE-only extensions like \K and [[:alpha:]] are not handled.
• Regex optimization suggestions — this tool only unfolds structure. ReDoS warnings and performance suggestions belong to dedicated tools like regex101.