FoundationAgents/MetaGPT · error · LineNumberError

Invalid start line number: {start}. Line numbers must be bet

Error message

Invalid start line number: {start}. Line numbers must be between 1 and {len(lines)} (inclusive).

What it means

Raised by Editor._edit_impl when the resolved start line is outside 1..len(lines). start defaults to 1 when None, so this fires only for explicitly supplied values: 0, negative numbers, values past the end of the file, or non-numeric garbage that survives comparison.

Source

Thrown at metagpt/tools/libs/editor.py:461

        Args:
            lines: list[str]: The lines in the original file.
            start: int: The start line number for editing.
            end: int: The end line number for editing.
            content: str: The content to replace the lines with.

        Returns:
            content: str: The new content of the file.
            n_added_lines: int: The number of lines added to the file.
        """
        # Handle cases where start or end are None
        if start is None:
            start = 1  # Default to the beginning
        if end is None:
            end = len(lines)  # Default to the end
        # Check arguments
        if not (1 <= start <= len(lines)):
            raise LineNumberError(
                f"Invalid start line number: {start}. Line numbers must be between 1 and {len(lines)} (inclusive)."
            )
        if not (1 <= end <= len(lines)):
            raise LineNumberError(
                f"Invalid end line number: {end}. Line numbers must be between 1 and {len(lines)} (inclusive)."
            )
        if start > end:
            raise LineNumberError(f"Invalid line range: {start}-{end}. Start must be less than or equal to end.")

        # Split content into lines and ensure it ends with a newline
        if not content.endswith("\n"):
            content += "\n"
        content_lines = content.splitlines(True)

        # Calculate the number of lines to be added
        n_added_lines = len(content_lines)

        # Remove the specified range of lines and insert the new content

View on GitHub (pinned to 11cdf466d0)

Solutions

1. Re-read the file and recompute line numbers immediately before editing
2. Convert 0-based indices to 1-based (add 1)
3. Validate 1 <= start <= len(lines) in your wrapper before delegating to the editor

Example fix

// before
editor.edit(path, start=0, end=3, content='x = 1\n')  # ValueError

// after
editor.edit(path, start=1, end=3, content='x = 1\n')

n = len(editor.current_file.read_text().splitlines())
start = min(max(1, int(start)), n)
end = min(max(start, int(end)), n)
editor.edit(path, start=start, end=end, content=content)

def valid_range(start: int, end: int, n: int) -> bool:
    return 1 <= start <= end <= n

try:
    editor.edit(path, start=s, end=e, content=c)
except LineNumberError as err:
    # re-read and recompute, then retry once with clamped values
    raise

When it happens

Trigger: editor.edit(path, start=0, end=5, content=...) or start beyond EOF; stale line numbers from a previous longer version of the file; 0-based indexing passed by mistake.

Common situations: Edits computed against outdated file snapshots (the file shrank since it was read); LLM agents guessing line numbers; converting 0-based diff hunks to 1-based incorrectly.

Related errors

• Line number must be between 1 and {total_lines}
• Invalid line number: {start}. Line numbers must be between 1
• Invalid end line number: {end}. Line numbers must be between
• Invalid line range: {start}-{end}. Start must be less than o
• Invalid file name.

AI-assisted analysis of FoundationAgents/MetaGPT@11cdf466d0 (2026-08-14). Data as JSON: /api/errors/9ae5691b5322dcff. Report an issue: GitHub.