Plain-English Explanations

One of RegexLens's most powerful features is its ability to break down any regex into human-readable steps. No more deciphering cryptic patterns—every component is explained clearly.

How It Works

RegexLens parses your regex into an Abstract Syntax Tree (AST), then traverses each node to generate a natural language explanation. This is deterministic, not AI-generated, so you get consistent, accurate explanations every time.

Example Breakdown

Let's look at a password validation regex:

^(?=.*[A-Z])(?=.*[a-z])(?=.*\d)(?=.*[@$!%*?&])[A-Za-z\d@$!%*?&]{8,}$

RegexLens explains this as:

Step	Explanation
1	Start of string
2	Positive lookahead: requires at least one uppercase letter (A-Z)
3	Positive lookahead: requires at least one lowercase letter (a-z)
4	Positive lookahead: requires at least one digit
5	Positive lookahead: requires at least one special character (@$!%*?&)
6	Match 8 or more characters from: letters, digits, or special characters
7	End of string

Try this pattern → (opens in a new tab)

Explanation Depth

Explanations are hierarchical, showing nested structures clearly:

(foo|bar)+

Explanation:

1. Capture group #1
   └─ Alternation: "foo" OR "bar"
2. One or more times

Hover Synchronization

Hover over any explanation step to highlight the corresponding part of your regex pattern. This bidirectional sync helps you understand exactly which part of the pattern each explanation refers to.

You can also:

Click to lock a highlight so it stays visible
Hover over the pattern to highlight the corresponding explanation

Supported Constructs

RegexLens explains all JavaScript regex features:

Basic Patterns

Literal characters
Character classes [abc] and [^abc]
Predefined classes \d, \w, \s, .
Anchors ^, $, \b, \B

Quantifiers

* (zero or more)
+ (one or more)
? (zero or one)
{n} (exactly n)
{n,} (n or more)
{n,m} (between n and m)
Lazy variants *?, +?, ??, {n,m}?

Groups

Capture groups (...) with numbered references
Named groups (?<name>...) with name display
Non-capturing groups (?:...)
Backreferences \1, \k<name>

Lookarounds

Positive lookahead (?=...)
Negative lookahead (?!...)
Positive lookbehind (?<=...)
Negative lookbehind (?<!...)

Alternation

Simple alternation foo|bar
Grouped alternation (foo|bar|baz)

Tips for Reading Explanations

Read top to bottom — Explanations follow the regex from left to right
Check indentation — Nested items are children of the parent construct
Look for quantifiers — They always follow what they quantify
Watch for anchors — ^ and $ define boundaries

Explanation Quality

RegexLens aims for explanations that are:

Accurate — Every explanation matches the actual regex behavior
Concise — No unnecessary verbosity
Actionable — You understand what the regex does, not just what it is
Educational — Learn regex concepts as you use the tool

Pattern Testing AST Viewer