kovidgoyal/kitty · warning

Ignoring invalid font feature: {feat}

Error message

Ignoring invalid font feature: {feat}

What it means

Within a font_features line, one of the feature tokens could not be parsed as a ParsedFontFeature (ValueError). The bad feature is skipped; other features on the line still apply.

Source

Thrown at kitty/options/utils.py:1084

    if ans and dict_with_parse_results is not None:
        dict_with_parse_results['map'] = [None]
    return ans


def font_features(val: str) -> Iterable[tuple[str, tuple[defines.ParsedFontFeature, ...]]]:
    if val == 'none':
        return
    parts = val.split()
    if len(parts) < 2:
        log_error(f'Ignoring invalid font_features {val}')
        return
    if parts[0]:
        features = []
        for feat in parts[1:]:
            try:
                features.append(defines.ParsedFontFeature(feat))
            except ValueError:
                log_error(f'Ignoring invalid font feature: {feat}')
        yield parts[0], tuple(features)


def modify_font(val: str) -> Iterable[tuple[str, FontModification]]:
    parts = val.split()
    pos, plen = 0, len(parts)
    if plen < 2:
        log_error(f'Ignoring invalid modify_font: {val}')
        return
    mtype: ModificationType | None = getattr(ModificationType, parts[pos], None)
    if mtype is None:
        log_error(f'Ignoring invalid modify_font with unknown modification type: {parts[pos]}')
        return
    pos += 1
    font_name = ''
    if mtype is ModificationType.size:
        font_name = parts[pos]
        pos += 1

View on GitHub (pinned to 6d5d0c4406)

Solutions

1. Use standard OpenType feature syntax: 4-character tag preceded by + or -, e.g. +ss01.
2. Remove the offending token and re-test.
3. Check the font's supported features with a tool like fonttools if unsure.

Example fix

# before
font_features FiraCode ss01 zero

# after
font_features FiraCode +ss01 +zero

import re
def valid_feature(tok: str) -> bool:
    return bool(re.fullmatch(r'[+-][a-zA-Z0-9]{4}', tok))

def is_ot_feature(tok: str) -> bool:
    return len(tok) == 5 and tok[0] in '+-' and tok[1:].isalnum()

When it happens

Trigger: A malformed feature token such as 'ss01' (missing +/-), '+ss0q' (invalid characters), or '+toolongfeaturename'.

Common situations: Typos in OpenType feature tags; forgetting the + or - prefix; using CSS-style syntax like 'ss01=1'.

Related errors

• Ignoring invalid font_features {val}
• Ignoring invalid modify_font: {val}
• Ignoring invalid modify_font with unknown modification type:
• Ignoring modify_font with invalid size: {sz}
• Percentage adjustments of {key} must be positive numbers

AI-assisted analysis of kovidgoyal/kitty@6d5d0c4406 (2026-08-27). Data as JSON: /api/errors/2f03d5cd43ff8643. Report an issue: GitHub.