Comparing regexes across flavors

Compare mode runs the same pattern and subject on multiple flavors at once so you can see validity, match results, fidelity, and key dialect differences side-by-side.

Open Compare

• Toolbar or right panel tab: Compare
• Keyboard: Ctrl+6 (⌘+6 on macOS)
• Ctrl+Enter re-runs the comparison

Select flavors (2–4)

Use the checkboxes at the top of the Compare panel. RegexCraft defaults to a useful set (for example .NET, PCRE2, JavaScript, and another flavor). You can change the selection at any time:

• Minimum: 2 flavors
• Maximum: 4 flavors

Comparisons re-run automatically when you change the pattern, subject, options, or flavor selection (with the same live debounce as Test mode).

What each card shows

For every selected flavor:

Field	Meaning
Header	Flavor name, testing engine, fidelity badge (Full / High / Approximate)
Valid / Invalid	Whether the pattern compiles on that flavor’s engine
Match count & timing	How many matches and how long Match took
First matches	Sample match lines with group summaries
Key notes	Dropped options, unsupported tokens detected in the pattern, fidelity notes, known differences

A summary strip above the cards lists cross-flavor differences (validity splits, match-count diffs, first-match offsets, option drops, unsupported constructs, fidelity mix).

Copy summary

Copy summary places a plain-text report on the clipboard: pattern, subject, per-flavor results, and cross-flavor notes. Useful for bug reports or sharing with teammates.

Options and fidelity

Compare uses the toolbar option checkboxes as the requested options, then applies each flavor’s support matrix (SupportedOptions). If JavaScript drops ExplicitCapture or free-spacing, that appears under Dropped options for that card.

Approximate flavors (Python, Go, Rust, …) still run on the closest real engine (.NET or PCRE2). Cards show the fidelity badge and note so you never confuse approximate testing with native dialect behavior. See Flavors & testing fidelity.

Layout (right panel width)

Compare needs far more horizontal space than Match or Replace. When you open Compare:

• The right panel expands to fill most of the window (star layout)
• The center becomes a narrow pattern-only strip (analysis tree is hidden while comparing)
• The left sidebar narrows slightly so cards get more room
• Result cards sit in a 2-column grid that fills the panel

When you switch to any other mode, the previous Normal layout is restored (full analysis tree, wider editor, remembered right-panel width).

The mode tabs (Test … Compare) scroll horizontally if the panel is narrow so labels are never clipped.

Tips

• Keep the subject short while exploring differences; Compare is optimized for interactive patterns, not multi-megabyte subjects.
• Use Test mode for deep highlighting of a single flavor; use Compare when you care about portability.
• If every selected flavor is invalid, fix the pattern syntax first (unclosed groups, etc.).
• Token palette dimming in the left sidebar remains driven by the main flavor dropdown; Compare cards call out unsupported constructs independently.
• If the panel feels tight after upgrading, open Compare once and drag the splitter — that width is remembered separately from Match mode.