chord_pro

A Dart parser for the ChordPro 6 song format.

Built for music apps and digital songbooks — parses .cho / .crd / .chopro files into typed chords, lyrics, metadata, comments, images, layout hints, and chord diagrams.

Installation

dart pub add chord_pro

Usage

Parse a document

import 'package:chord_pro/chord_pro.dart';

final result = ChordPro.parse(source);
final song = result.songs.first;

print(song.metadata.titles.firstOrNull);
print(song.metadata.key);

ChordPro.parse returns a ParseResult with every song in the document (split on {new_song} / {ns}) plus any diagnostics. Use ChordPro.parseSong if you only want the first song.

What a Song contains

• metadata — typed Metadata: titles, sort titles, subtitles, artists, sort artist, composers, lyricists, arrangers, copyright, album, year, key, time, tempo, duration, capo, transpose (plus transposeQualifier), columns, tags, plus an other map for anything custom.
• sections — ordered Sections for verse, chorus, bridge, tab, grid, abc, ly, svg, textblock, custom environments, and loose lines. Each section exposes label, attributes, plus typed gridAttributes and textblockAttributes where applicable.
• chordDefinitions — parsed {define} / {chord} bodies including display, format, keys, copy, copyall, diagram, and the transposable bracketed [Name] form.
• 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.
• tocSuppressed — true when {ns toc=no} requested the song be omitted from the table of contents.
• titlesAlignment — typed {titles} alignment hint.
• diagrams — typed {diagrams} (or {g}) setting (enabled flag plus position enum).
• transposed(semitones) — returns a copy with every chord shifted.

Walk sections and lines

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}');
    }
  }
}

Transpose and conditional selectors

Shift every chord by N semitones:

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

Activate conditional directives like {title-guitar: …} / {title-guitar!: …} by passing a selector set:

final guitar = ChordPro.parseSong(source, selectors: {'guitar'});

The selector set gates metadata, formatting, sections, comments, images, layout breaks, chord recalls, and {define} / {chord} definitions. Matching is case-insensitive.

Supported features

All facts per the ChordPro chord reference and directive reference.

Chords

• Letter roots A–G, Nashville 1–7, Roman I–VII.
• Sharps and flats: #, b.
• Slash bass.
• Minor variants: m, mi, min, -.
• Major qualifier maj and the spec alternate ^.
• Diminished dim / 0, half-diminished h.
• Augmented aug and the spec alternate +.
• sus, sus2, sus4, add.
• Emergency-bracket recovery (ChordPro 6.020/6.080): [ ]+ and [|] parse as annotations; empty [] is a zero-width placeholder.

Directives

• Metadata — title / t, sorttitle, subtitle / st, artist, sortartist, composer, lyricist, arranger, copyright, album, year, key, time, tempo, duration, capo, transpose (with optional s/f/k/#/b/♯/♭ qualifier), columns / col, tag, plus {meta: key value} desugaring. Auto-generated names (_key, key.print, today, …) are reserved.
• Comments — {comment}, {ci}, {cb}, {highlight} emit as in-flow comment lines.
• Images — {image: …} parsed into a typed ImageDirective with full attribute coverage: src, width, height, scale, align, border, bordertrbl, title, label, href, id, chord, type, x, y, spread, center, persist, omit, plus a validated anchorEnum (paper / page / allpages / column / float / line).
• Layout breaks — {new_page}, {new_physical_page}, {column_break} emit as in-flow layout breaks.
• Output / song boundary — {ns toc=no} (or toc=false / toc=0) sets Song.tocSuppressed. {titles: left|center|right} and {diagrams: on|off|top|bottom|right|below} (with {g} alias) become typed song-level settings.
• Formatting — chordfont, textsize, titlecolour, … reduce into FormattingSettings. Both colour and color accepted.
• Custom — x_* extensions preserved on Song.customExtensions.

Sections

• Built-in environments: verse / sov, chorus / soc, bridge / sob, tab / sot, grid / sog.
• Delegated abc, ly, svg, textblock captured verbatim.
• Custom start_of_<name> / end_of_<name> sections preserved with their custom kind.
• label="…" attribute parsed for every {start_of_*} (alongside the legacy bare-value form).
• {start_of_grid} exposes typed shape (left+measures × beats+right), cc, and label via Section.gridAttributes.
• {start_of_textblock} exposes the full ChordPro 6.050 attribute set (textblock-specific plus image-inherited) via Section.textblockAttributes.
• {chorus} recall accepts all four spec forms — {chorus}, {chorus: Final}, {chorus: label="Final"}, {chorus label="Final"}.

Conditional selectors

• Positive form {title-guitar: …} and spec-form negation {title-guitar!: …}.
• Gates metadata, formatting, sections, comments, images, layout breaks, chord recalls, and {define} / {chord} definitions.

Source features

• ChordPro 6.01 scanner: trailing \ line continuation and \uXXXX Unicode escapes anywhere in input text.
• ChordPro 6.060 brace-form \u{X+} Unicode escape (1+ hex digits, supports surrogate-pair recombination).
• File-level # comments dropped.
• Diagnostics with 1-based source spans for every problem.

Non-spec extensions

The parser is more lenient than the published spec in a few places. Each extension is opt-in by simply being present in your input — files parse either way, but the named feature is not required by ChordPro itself.

Extension	Spec equivalent	Notes
H letter root	B	German notation for B natural.
♯ (U+266F), ♭ (U+266D)	#, b	Unicode accidentals.
ø, °	h, 0 / dim	Half-diminished and diminished glyphs.
NC, N.C., N.C	—	No-chord markers; spec is silent.
Backslash escapes inside lyrics	—	Escape [, ], {, }, \ inside lyric lines.
Mid-lyric {…} directives	—	Spec requires directives to occupy a whole line.
{name-!sel}, {name+sel}	{name-sel!}	Legacy negative-selector forms; new files use the spec form.

Known limitations

• Pango-style markup (<b>, <i>, <span …>, <sym …/>, <img …/>, <strut …/>) inside lyrics and comments is preserved verbatim — no inline parsing or rendering.
• {define format="…"} is captured as a typed String but the %{…} substitutions inside it are not interpreted (rendering concern).
• The directive parser closes on the first unescaped }, so attribute values cannot themselves contain a literal }.
• {pagetype} lands in Song.directives only — no typed access.

Example songs

Runnable demo: example/chord_pro_example.dart.

ChordPro source files:

• knockin_on_heavens_door.cho
• house_of_the_rising_sun.cho
• scarborough_fair.cho