kovidgoyal/kitty · warning · ValueError

Invalid characters in visual_window_select_characters: {x} O

Error message

Invalid characters in visual_window_select_characters: {x} Only numbers (0-9) and alphabets (a-z,A-Z) are allowed. Ignoring.

What it means

visual_window_select_characters validator raises this when, after uppercasing, the set of characters contains anything outside digits, ASCII uppercase, and the punctuation "-=[]\\;',./`". kitty uses these characters to label windows during visual window selection mode.

Source

Thrown at kitty/options/utils.py:818

        return positive_float(parts[0]), -1.0
    return positive_float(parts[0]), positive_float(parts[1])


def resize_debounce_time(x: str) -> tuple[float, float]:
    parts = x.split(maxsplit=1)
    if len(parts) == 1:
        return positive_float(parts[0]), 0.5
    return positive_float(parts[0]), positive_float(parts[1])


def visual_window_select_characters(x: str) -> str:
    import string

    valid_characters = string.digits + string.ascii_uppercase + "-=[]\\;',./`"
    ans = x.upper()
    ans_chars = set(ans)
    if not ans_chars.issubset(set(valid_characters)):
        raise ValueError(f'Invalid characters in visual_window_select_characters: {x} Only numbers (0-9) and alphabets (a-z,A-Z) are allowed. Ignoring.')
    if len(ans_chars) < len(x):
        raise ValueError(f'Invalid characters in visual_window_select_characters: {x} Contains identical numbers or alphabets, case insensitive. Ignoring.')
    return ans


def tab_separator(x: str) -> str:
    for q in '\'"':
        if x.startswith(q) and x.endswith(q):
            x = x[1:-1]
            if not x:
                return ''
            break
    if not x.strip():
        x = ('\xa0' * len(x)) if x else default_tab_separator
    return x


def tab_bar_edge(x: str) -> int:

View on GitHub (pinned to 6d5d0c4406)

Solutions

1. Restrict to 0-9, a-z/A-Z and the allowed punctuation set
2. Keep the default or extend only with allowed punctuation characters

Example fix

# before
visual_window_select_characters 0123456789abcdef!@
# after
visual_window_select_characters 0123456789abcdef

import string
ALLOWED = set(string.digits + string.ascii_uppercase + "-=[]\\;',./`")
def valid_vwsc(x: str) -> bool:
    return set(x.upper()).issubset(ALLOWED)

When it happens

Trigger: Setting visual_window_select_characters to include spaces, unicode letters, or other punctuation like '!' or '@'.

Common situations: Wanting more selectable windows than the default 0-9A-Z allows and adding invalid symbols.

Understand the failure class

• Parsing and encoding errors: unexpected token, malformed input — why parsers reject input and how to find the real culprit.

Related errors

• The window layout {p} is unknown
• Invalid characters in visual_window_select_characters: {x} C
• This should be run as kitten broadcast
• No option named: {k}
• No custom kitten named {kitten} found

AI-assisted analysis of kovidgoyal/kitty@6d5d0c4406 (2026-08-27). Data as JSON: /api/errors/3c5a00260e2deb3a. Report an issue: GitHub.