RicoSuter/NSwag · error · ArgumentException

The given schema type is not supported.

Error message

The given schema type is not supported.

What it means

CreateJsonSerializerContractResolver configures JSON serializer settings per schema type but only has branches for Swagger2 and OpenApi3; anything else throws ArgumentException('The given schema type is not supported.'). It is a private factory called by the cached resolver providers for known types.

Solutions

1. Pass only SchemaType.Swagger2 or SchemaType.OpenApi3
2. Validate/normalize the schema type before serialization
3. Upgrade NSwag if a newer schema type is expected to be supported

Example fix

// before
var resolver = GetJsonSerializerContractResolver(schemaType);
// after
if (schemaType != SchemaType.Swagger2 && schemaType != SchemaType.OpenApi3)
    throw new ArgumentException($"Unsupported schema type: {schemaType}");
var resolver = GetJsonSerializerContractResolver(schemaType);

var supported = new[] { SchemaType.Swagger2, SchemaType.OpenApi3 };
if (!supported.Contains(schemaType)) throw new ArgumentException(nameof(schemaType));

bool resolverSupported = schemaType == SchemaType.Swagger2 || schemaType == SchemaType.OpenApi3;

When it happens

Trigger: Invoking the contract resolver factory with a SchemaType other than Swagger2/OpenApi3, typically via GetJsonSerializerContractResolver with an invalid enum value.

Common situations: A SchemaType field set from unvalidated input, or a new enum value added in a newer NSwag version being passed to an older runtime.

Related errors

• The schema type '" + schemaType + "' is not supported.
• The schema type JsonSchema is not supported.
• This UI does not support multiple documents per UI: Do not…
• The SwaggerUiRoute cannot contain
• The NSwag DI services are not registered: Call…

AI-assisted analysis of RicoSuter/NSwag@63daf8fcc3 (2026-09-14). Data as JSON: /api/errors/a671a57a975de36d. Report an issue: GitHub.

Appendix: source

Thrown at src/NSwag.Core/OpenApiDocument.Serialization.cs:110

                //resolver.IgnoreProperty(typeof(SwaggerResponse), "produces");

                resolver.IgnoreProperty(typeof(OpenApiDocument), "definitions");
                resolver.IgnoreProperty(typeof(OpenApiDocument), "parameters");
                resolver.IgnoreProperty(typeof(OpenApiDocument), "responses");
                resolver.IgnoreProperty(typeof(OpenApiDocument), "securityDefinitions");

                resolver.IgnoreProperty(typeof(OpenApiResponse), "schema");
                resolver.IgnoreProperty(typeof(OpenApiResponse), "examples");
                resolver.IgnoreProperty(typeof(OpenApiResponse), "x-nullable");

                resolver.IgnoreProperty(typeof(OpenApiSecurityScheme), "flow");
                resolver.IgnoreProperty(typeof(OpenApiSecurityScheme), "authorizationUrl");
                resolver.IgnoreProperty(typeof(OpenApiSecurityScheme), "tokenUrl");
                resolver.IgnoreProperty(typeof(OpenApiSecurityScheme), "scopes");
            }
            else
            {
                throw new ArgumentException("The given schema type is not supported.");
            }

            return resolver;
        }

        private ObservableCollection<OpenApiSchema> _schemes = [];
        internal List<string> _consumes = [];
        internal List<string> _produces = [];

        /// <summary>Gets or sets the host (name or ip) serving the API (Swagger only).</summary>
        [JsonProperty(PropertyName = "host", Order = 5, DefaultValueHandling = DefaultValueHandling.IgnoreAndPopulate)]
        public string Host
        {
            get => Servers?.FirstOrDefault()?.Url?.Replace("http://", "").Replace("https://", "").Split('/')[0];
            set => UpdateServers(Schemes, value, BasePath);
        }

        /// <summary>Gets or sets the base path on which the API is served, which is relative to the <see cref="Host"/>.</summary>

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