RegexCraft

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Testing Regular Expressions

Testing Regular Expressions

This guide covers the Test panel, highlighting, groups, engines, and options. Replace, Split, Generate, and GREP share the same right-hand panel host.

Layout

Area Purpose
Toolbar Flavor, Match / Replace / Split / Generate / GREP modes, Options, theme
Tokens / Library / History (left) Insert constructs, save/load patterns, searchable history
Regex Editor (center) AvaloniaEdit with professional regex syntax highlighting
Analysis Tree (center bottom) Live hierarchical explanation — click a node to select it in the editor
Test / Replace / Split / Generate / GREP (right) Subject, match highlighting, groups, replace/split/codegen/file search — panels fill available space
Status bar Flavor, engine, counts, timing, shortcut hints
Splitters Drag to resize left sidebar, center, and right panel

Match testing

  1. Choose a flavor in the toolbar (.NET, PCRE2, JavaScript, Python, PHP, …). See Flavors & testing fidelity.
  2. If testing is approximate, read the blue fidelity banner so you know which engine is actually running.
  3. Enter a pattern in the Regex Editor (or click tokens from the left).
  4. Enter or edit the Subject text on the right (Test tab).
  5. Results update live (debounced) as you type. Click Run or press Ctrl+Enter for an immediate run.

Highlighting

Matches are painted in the subject editor:

  • Full match — yellow/gold style (MatchHighlight)
  • Groups — rotating blues/greens/warm accents (GroupHighlight0–3)

These colors come from the theme dictionaries and work in light and dark mode.

Groups list

Each match expands to show capturing groups:

  • Numbered groups (G1, G2, …)
  • Named groups (G1/user)
  • Index + length for each successful capture
  • Copy — copy the match or group value to the clipboard
  • Go — select that range in the subject editor

Empty state: when there are no matches, a short message explains why (no matches vs pattern error).

Analysis Tree

The analysis tree is a live structural breakdown of the pattern:

  • Sequences, alternations, quantifiers (with greedy/lazy/possessive notes)
  • Capturing, named, non-capturing, atomic groups
  • Lookaheads / lookbehinds
  • Character classes, escapes, anchors, Unicode properties
  • Incomplete patterns degrade gracefully with error nodes

Click a node to select the corresponding fragment in the Regex Editor.

Switching engines

Change the flavor dropdown between .NET and PCRE2. RegexCraft re-runs the current Test/Replace/Split automatically.

The status bar shows:

Flavor: .NET | Engine: .NET    Matches: 2    Time: 0.35 ms

Invalid patterns

If the pattern cannot be compiled by the active engine, an error banner appears on the right and highlights are cleared. The Analysis Tree may still show a partial structure for incomplete syntax (for example an unclosed ().

Options

Open Options in the toolbar (expanded by default in Phase 2):

  • Ignore case
  • Multiline
  • Singleline
  • Explicit capture
  • Ignore pattern whitespace

The options strip labels which flavor/engine the options apply to. Changing any option re-runs the active mode.

Tokens

  • Search by label, insert text, or category
  • Click inserts at the caret (or replaces the selection) and restores focus to the editor
  • Tokens with limited engine support appear slightly dimmed with a tooltip note