What causes "start line is less than 1: %d" in plandex-ai/plandex?

Convert any 0-based numbering to 1-based before constructing the section

start line is less than 1: %d

Error message

start line is less than 1: %d

What it means

GetLinesWithPrefix enforces 1-based line numbers; a parsed start line of 0 or negative is invalid and rejected with this error. It typically results from parsing a 0, a malformed marker, or a prefix that stripped all digits.

Source

Thrown at app/shared/streamed_change.go:71

	} else {
		endLine, err = ExtractLineNumberWithPrefix(streamedChangeSection.EndLineString, prefix)

		if err != nil {
			log.Printf("Error extracting end line number: %v\n", err)
			return 0, 0, fmt.Errorf("error extracting end line number: %v", err)
		}
	}

	log.Printf("StartLine: %d, EndLine: %d\n", startLine, endLine)

	if startLine > endLine {
		log.Printf("Start line is greater than end line: %d > %d\n", startLine, endLine)
		return 0, 0, fmt.Errorf("start line is greater than end line: %d > %d", startLine, endLine)
	}

	if startLine < 1 {
		log.Printf("Start line is less than 1: %d\n", startLine)
		return 0, 0, fmt.Errorf("start line is less than 1: %d", startLine)
	}

	return startLine, endLine, nil
}

func ExtractLineNumber(line string) (int, error) {
	return ExtractLineNumberWithPrefix(line, "pdx-")
}

func ExtractLineNumberWithPrefix(line, prefix string) (int, error) {
	// Split the line at the first space to isolate the line number
	parts := strings.SplitN(line, " ", 2)

	// Remove the colon from the line number part
	lineNumberStr := strings.TrimSuffix(parts[0], ":")
	lineNumberStr = strings.TrimPrefix(lineNumberStr, prefix)
	if lineNumberStr == "" {
		return 0, fmt.Errorf("no line number found")

View on GitHub (pinned to e2d772072e)

Solutions

Convert any 0-based numbering to 1-based before constructing the section
Ensure the start marker is present and numeric (guard empty StartLineString earlier)
Clamp/validate: if parsed start is 0, treat as 1 or reject before calling GetLines
Re-stream the section if the marker was truncated

Example fix

// before
start, end, err := GetLinesWithPrefix(section, prefix) // start=0 -> error
// after
if start, err = ExtractLineNumberWithPrefix(section.StartLineString, prefix); err == nil && start == 0 { start = 1 }
start, end, err = GetLinesWithPrefix(section, prefix)

Defensive patterns

Strategy: validation

Validate before calling

func startLineAtLeastOne(section shared.StreamedChangeSection, prefix string) error {
    s, err := shared.ExtractLineNumberWithPrefix(section.StartLineString, prefix)
    if err != nil { return err }
    if s < 1 { return fmt.Errorf("start line %d < 1", s) }
    return nil
}

Try / catch

start, end, err := GetLinesWithPrefix(section, prefix)
if err != nil {
    if strings.Contains(err.Error(), "less than 1") {
        return fmt.Errorf("1-based line numbers required; got 0-based marker %q", section.StartLineString)
    }
    return err
}

Prevention

Convert 0-based numbering to 1-based when building sections
Reject or clamp markers parsing to 0 before calling GetLines
Document/enforce 1-based line markers across tooling

When it happens

Trigger: GetLines with StartLineString parsing to < 1 — e.g. marker "0", or prefix trimming leaving no/zero digits (often accompanying "no line number found" upstream in similar paths).

Common situations: Model emitting 0-based line numbers while the library expects 1-based; empty section lines parsed as line 0.

Related errors

AI-assisted analysis of plandex-ai/plandex@e2d772072e (2026-09-05). Data as JSON: /api/errors/ee709cc567c76169. Report an issue: GitHub.