{"record":{"id":"cd18562f448459b8","repo":"googleapis/mcp-toolbox","slug":"parameter-type-field-must-be-a-string-got-t","errorCode":null,"errorMessage":"parameter 'type' field must be a string, got %T","messagePattern":"parameter 'type' field must be a string, got %T","errorType":"validation","errorClass":null,"httpStatus":null,"severity":"error","filePath":"internal/util/parameters/parameters.go","lineNumber":398,"sourceCode":"}\n\n// parseParamFromDelayedUnmarshaler is a helper function that is required to parse\n// parameters because there are multiple different types\nfunc parseParamFromDelayedUnmarshaler(ctx context.Context, u *util.DelayedUnmarshaler) (Parameter, error) {\n\tvar p map[string]any\n\terr := u.Unmarshal(&p)\n\tif err != nil {\n\t\treturn nil, fmt.Errorf(\"error parsing parameters: %w\", err)\n\t}\n\n\tt, ok := p[\"type\"]\n\tif !ok {\n\t\treturn nil, fmt.Errorf(\"parameter is missing 'type' field\")\n\t}\n\n\ttypeStr, ok := t.(string)\n\tif !ok {\n\t\treturn nil, fmt.Errorf(\"parameter 'type' field must be a string, got %T\", t)\n\t}\n\n\tparam, err := ParseParameter(ctx, p, typeStr)\n\tif err != nil {\n\t\treturn nil, err\n\t}\n\n\tif err := validateParameter(param); err != nil {\n\t\treturn nil, err\n\t}\n\n\treturn param, nil\n}\n\n// ParseParameter parses a raw map into a Parameter object based on its \"type\" field.\nfunc ParseParameter(ctx context.Context, p map[string]any, paramType string) (Parameter, error) {\n\tdec, err := util.NewStrictDecoder(p)\n\tif err != nil {","sourceCodeStart":380,"sourceCodeEnd":416,"githubUrl":"https://github.com/googleapis/mcp-toolbox/blob/8cc6e09de2ad7b8bffc77751799585a1401a48eb/internal/util/parameters/parameters.go#L380-L416","documentation":"parseParamFromDelayedUnmarshaler type-asserts the 'type' key of a raw parameter map to string. The error fires during config parsing when the parameter's 'type' key in tools.yaml is a non-string YAML value (e.g. a number, list, or nested map), reporting the offending Go type via %T.","triggerScenarios":"Thrown at internal/util/parameters/parameters.go:398 when the library encounters an invalid state.","commonSituations":"See trigger scenarios.","solutions":["Quote the 'type' value so YAML parses it as a string (e.g. type: \"string\")","Replace a list or mapping value with a valid scalar type name"],"exampleFix":null,"handlingStrategy":"validation","validationCode":null,"typeGuard":null,"tryCatchPattern":null,"preventionTips":[],"tags":[],"backgroundTag":null,"analyzedSha":"8cc6e09de2ad7b8bffc77751799585a1401a48eb","analyzedAt":"2026-09-05T01:10:36.887Z","contentChangedAt":"2026-09-05T01:10:36.887Z","schemaVersion":2},"datasetVersion":"2026-09-08T10:18:20.063Z"}