LykosAI/StabilityMatrix · error · InvalidDataException

Invalid metadata JSON, expected property name but got

Error message

Invalid metadata JSON, expected property name but got {reader.TokenType}.

What it means

While iterating the JSON header, every top-level entry must be a property (name/value pair). This throw indicates the reader encountered a token other than PropertyName where an object key was expected, meaning the header JSON structure deviates from the safetensors metadata schema.

Solutions

Validate the header JSON with a standard parser to find the malformed region.
Re-export the file with a compliant safetensors writer.
Update parsing to skip unexpected token types instead of throwing, if tolerable.
Inspect reader.TokenType in the message to identify what the stray token is.

Defensive patterns

Strategy: try-catch

Validate before calling

// Pre-validate header JSON structure with System.Text.Json
var json = System.Text.Encoding.UTF8.GetString(headerBytes, 8, headerBytes.Length - 8);
using var doc = System.Text.Json.JsonDocument.Parse(json);
if (doc.RootElement.ValueKind != System.Text.Json.JsonValueKind.Object)
    throw new InvalidDataException("Safetensors header is not a JSON object.");

Try / catch

try { var meta = await SafetensorMetadata.ParseAsync(stream); }
catch (InvalidDataException ex) { _logger.LogWarning(ex, "Skipping nonstandard metadata"); return SafetensorMetadata.Empty; }

Prevention

Reject model files from untrusted converters
Validate header JSON schema before deep parsing
Keep converter tooling up to date

When it happens

Trigger: Header JSON containing unexpected tokens (e.g. bare values, nested arrays at top level) after skipping entries — typically malformed or nonstandard safetensors headers.

Common situations: Files produced by nonstandard exporters, corrupted headers, hand-edited metadata blocks.

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

AI-assisted analysis of LykosAI/StabilityMatrix@af93d6ef57 (2026-09-12). Data as JSON: /api/errors/ec7b8e02fccc6b38. Report an issue: GitHub.

Appendix: source

Thrown at StabilityMatrix.Core/Models/SafetensorMetadata.cs:91

                // expecting a JSON object
                throw new InvalidDataException("JSON does not start with '{'.");
            }

            while (reader.Read())
            {
                // for each property in the object
                if (reader.TokenType == JsonTokenType.EndObject)
                {
                    // end of the object, no "__metadata__" found
                    // return true to indicate that we successfully read the JSON
                    // but it does not contain metadata
                    return null;
                }

                if (reader.TokenType != JsonTokenType.PropertyName)
                {
                    // expecting a property name
                    throw new InvalidDataException(
                        $"Invalid metadata JSON, expected property name but got {reader.TokenType}."
                    );
                }

                if (reader.ValueTextEquals("__metadata__"))
                {
                    if (JsonSerializer.Deserialize<Dictionary<string, string>>(ref reader) is { } dict)
                    {
                        return FromDictionary(dict);
                    }

                    // got null from Deserialize
                    throw new InvalidDataException("Failed to deserialize metadata.");
                }
                else
                {
                    // skip the property value
                    reader.Skip();

View on GitHub (pinned to af93d6ef57)