ChordPro

A Dart parser for the ChordPro 6 file format. Built for music app developers and digital songbook tooling: extract chords, lyrics, metadata, comments, images, layout hints and chord diagrams from .cho/.crd/.chopro files.

Using

import 'package:chord_pro/chord_pro.dart';

final result = ChordPro.parse(source);
for (final song in result.songs) {
  print(song.metadata.titles.firstOrNull);
  for (final section in song.sections) {
    print('${section.kind} ${section.label ?? ''}');
    for (final line in section.lines) {
      switch (line.kind) {
        case LineKind.structured:
          for (final token in line.tokens) {
            // TextToken / ChordToken / AnnotationToken / InlineDirectiveToken
          }
        case LineKind.verbatim:
          print(line.verbatim);
        case LineKind.comment:
          print('${line.commentStyle}: ${line.comment}');
        case LineKind.image:
          print('image: ${line.image?.src}');
        case LineKind.layoutBreak:
          print('break: ${line.layoutBreak}');
      }
    }
  }
}

// Transposition.
final upTwo = ChordPro.parseSong(source).transposed(2);

// Conditional selectors (e.g. instrument-specific titles).
final guitar = ChordPro.parseSong(source, selectors: {'guitar'});

ChordPro.parse returns a ParseResult with every song in the document (split on {new_song} / {ns}) plus any diagnostics. ChordPro.parseSong is a convenience that returns the first song. Pass selectors: to activate conditional directives — see below.

Each Song exposes:

• metadata — typed Metadata with titles, sort titles, subtitles, artists, sort artist, composers, lyricists, copyright, album, year, key, time, tempo, duration, capo, transpose, columns, tags and an other map for anything custom.
• sections — ordered Sections for verses, choruses, bridges, tabs, grids, abc, ly, svg, textblock and custom environments, plus loose lines.
• chordDefinitions — parsed {define} / {chord} bodies.
• formatting — typed font/size/colour overrides for chord, text, title, chorus, label and friends.
• directives — the raw directive stream in source order.
• customExtensions — x_* namespaced directives.
• transposed(semitones) — returns a copy with every chord shifted.

Supported features

• Spec-conformant chord notation per the ChordPro reference: letter roots (A–G), Nashville (1–7), Roman (I–VII); sharps and flats (#/b); slash bass; minor variants m/mi/min/-; major qualifiers maj and the spec alternate ^; diminished dim and the literal-zero 0; half-diminished h; aug, sus/sus2/ sus4, add.
• Conditional directives — both positive ({title-guitar: …}) and spec-form negation ({title-guitar!: …}, with ! postfixed on the selector per the ChordPro reference parser). Pass selectors: to ChordPro.parse / parseSong to activate them; the same set gates metadata, formatting, sections, comments, images, layout breaks, chord recalls, and {define}/{chord} definitions.
• All section environments — verse/sov, chorus/soc, bridge/ sob, tab/sot, grid/sog, plus delegated abc, ly, svg and textblock captured verbatim. Custom start_of_<name> / end_of_<name> sections preserved with their custom kind.
• All metadata directives from the spec — title/t, sorttitle, subtitle/st, artist, sortartist, composer, lyricist, copyright, album, year, key, time, tempo, duration, capo, transpose, columns/col, tag — plus {meta: key value} desugaring.
• Comment family ({comment}, {ci}, {cb}, {highlight}) emitted as in-flow comment lines.
• {image: …} parsed into a typed ImageDirective.
• Page-break and column-break directives as in-flow layout breaks ({new_page}, {new_physical_page}, {column_break}).
• Font/size/colour directives (chordfont, textsize, titlecolour, …) reduced into FormattingSettings. Both colour and the American color spelling are accepted.
• Custom x_* extensions preserved on Song.customExtensions and silently ignored by typed reduction (per spec).
• File-level # comments dropped.
• ChordPro 6.01 features: trailing \-line continuation and \uXXXX Unicode escapes in any input text.
• Diagnostics with 1-based source spans for every problem.

Non-spec extensions

For ergonomic reasons this parser is more lenient than the published spec in a few places. Each is opt-in by simply being present in the input — your file will still parse, but the named feature is not required by ChordPro itself:

• H as a letter root (German notation for B natural).
• Unicode accidentals ♯ (U+266F) and ♭ (U+266D).
• Half-diminished ø and diminished ° glyphs (the spec marks these as h and 0/dim).
• No-chord markers NC, N.C., N.C (the spec is silent).
• Backslash-escapes for [, ], {, }, \ inside lyric lines.
• {…} directives appearing mid-lyric (the spec requires directives to occupy a whole line).
• Legacy negative-selector forms {name-!sel} and {name+sel}, retained for backward compatibility with older files. New files should use the spec form {name-sel!}.

Known limitations

• The label="value" form for section labels is parsed as raw value text; only the bare {start_of_verse: Verse 1} form is mapped to Section.label.
• Pango-style markup (<b>, <i>, <span …>, <sym …/>, <img …/>, <strut …/>) inside lyric/comment text is preserved verbatim — no inline parsing is performed.
• {define}'s format argument and the associated \%{ escape are passed through as raw value text.
• The legacy/no-op directives pagetype, grid, no_grid, titles, and diagrams land in Song.directives only — they are not given typed access.

Example of chordpro format

example song