LykosAI/StabilityMatrix · warning · ValidationException

Unable to locate starting marker of last line

Error message

Unable to locate starting marker of last line

What it means

GenerationParameters.TryParse/Parse parses PNG-embedded generation-parameter text from A1111-style images. The parser expects the last non-empty line to begin with 'Steps:'; if it does not, the format is not recognized and a ValidationException is thrown naming the missing marker.

Solutions

1. Ensure the last line of the parameter text starts with 'Steps:' before parsing
2. Check the image metadata source — re-export or regenerate the image with a tool that embeds standard A1111 parameter blocks
3. Wrap TryParse in a try-catch and treat ValidationException as 'parameters not parseable' rather than a crash

Example fix

// before
var pars = GenerationParameters.Parse(text);
// after
if (GenerationParameters.TryParse(text, out var pars)) { /* use pars */ } else { /* fall back to defaults */ }

var ok = text.Split("\r\n").LastOrDefault(l => !string.IsNullOrWhiteSpace(l))?.StartsWith("Steps:") == true;
if (!ok) /* handle unparsable parameters */;

try { pars = GenerationParameters.Parse(text); } catch (ValidationException ex) { log.Warn(ex, "params unparsable"); pars = null; }

When it happens

Trigger: Calling Parse (via TryParse) with text whose final line does not start with 'Steps:' — e.g. truncated prompt text, images saved by tools that reorder/omit the Steps line, or manually edited parameter blocks.

Common situations: Importing images generated by WebUI forks or other tools that write parameters in a different order; a paste/copy of parameter text missing the trailing Steps line; corrupted or trimmed metadata.

Understand the failure class

Background: Schema validation failed / invalid input schema: payload rejected because its shape doesn't match the expected schema — this error's family across 28 libraries.

Related errors

• Fields line not found
• Invalid Token
• Sampler not selected
• Scheduler not selected
• Resources.Validation_PackageNameCannotBeEmpty

AI-assisted analysis of LykosAI/StabilityMatrix@af93d6ef57 (2026-09-12). Data as JSON: /api/errors/faf445b2df799e57. Report an issue: GitHub.

Appendix: source

Thrown at StabilityMatrix.Core/Models/GenerationParameters.cs:79

    }

    public static GenerationParameters Parse(string text)
    {
        var lines = text.Split('\n');

        if (lines.LastOrDefault() is not { } lastLine)
        {
            throw new ValidationException("Fields line not found");
        }

        if (lastLine.StartsWith("Steps:") != true)
        {
            lines = text.Split("\r\n");
            lastLine = lines.LastOrDefault() ?? string.Empty;

            if (lastLine.StartsWith("Steps:") != true)
            {
                throw new ValidationException("Unable to locate starting marker of last line");
            }
        }

        // Join lines before last line, split at 'Negative prompt: '
        var joinedLines = string.Join("\n", lines[..^1]).Trim();

        // Apparently there is no space after the colon if value is empty, so check and add space here
        if (joinedLines.EndsWith("Negative prompt:"))
        {
            joinedLines += ' ';
        }

        var splitFirstPart = joinedLines.Split("Negative prompt: ", 2);

        var positivePrompt = splitFirstPart.ElementAtOrDefault(0)?.Trim();
        var negativePrompt = splitFirstPart.ElementAtOrDefault(1)?.Trim();

        // Parse last line

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