github/github-mcp-server · error

each issue_fields item must be an object

Error message

each issue_fields item must be an object

What it means

optionalIssueWriteFields (pkg/github/issues.go:246) validates the issue_fields argument of issue write tools. This error fires when issue_fields IS an array ([]any from JSON) but one of its elements is not a JSON object — e.g. a bare string, number, or nested array. Each element must be a map like {"field_name": ..., "value": ...} or {"field_name": ..., "delete": true}.

Source

Thrown at pkg/github/issues.go:246

	TextValue struct {
		Field IssueFieldRef
		Value githubv4.String
	} `graphql:"... on IssueFieldTextValue"`
}

func optionalIssueWriteFields(args map[string]any) ([]issueWriteFieldInput, error) {
	issueFieldsRaw, exists := args["issue_fields"]
	if !exists {
		return nil, nil
	}

	var inputMaps []map[string]any
	switch v := issueFieldsRaw.(type) {
	case []any:
		for _, item := range v {
			itemMap, ok := item.(map[string]any)
			if !ok {
				return nil, fmt.Errorf("each issue_fields item must be an object")
			}
			inputMaps = append(inputMaps, itemMap)
		}
	case []map[string]any:
		inputMaps = v
	default:
		return nil, fmt.Errorf("issue_fields must be an array")
	}

	issueFields := make([]issueWriteFieldInput, 0, len(inputMaps))
	for _, itemMap := range inputMaps {
		fieldName, err := RequiredParam[string](itemMap, "field_name")
		if err != nil || strings.TrimSpace(fieldName) == "" {
			return nil, fmt.Errorf("field_name is required for each issue_fields item")
		}

		fieldOptionName, err := OptionalParam[string](itemMap, "field_option_name")
		if err != nil {

View on GitHub (pinned to 0ea1f775a7)

Solutions

1. Make every issue_fields element an object with at least field_name: [{"field_name":"Priority","value":"P0"}]
2. Re-read the tool's input schema: issue_fields is an array of objects
3. If generating args programmatically, serialize a typed struct ([]issueWriteFieldInput) instead of hand-built any slices

Example fix

# before
{"issue_fields": ["Priority", "P0"]}

# after
{"issue_fields": [{"field_name": "Priority", "field_option_name": "P0"}]}

raw, ok := args["issue_fields"]
if !ok {
    return nil // absent is fine
}
items, ok := raw.([]any)
if !ok {
    return errors.New("issue_fields must be an array")
}
for _, item := range items {
    if _, ok := item.(map[string]any); !ok {
        return errors.New("each issue_fields item must be an object")
    }
}

func isIssueFieldItem(v any) bool {
    _, ok := v.(map[string]any)
    return ok
}

When it happens

Trigger: Calling update_issue (or create_issue) with issue_fields=["Priority"] or issue_fields=["field_name","value"] instead of issue_fields=[{"field_name":"Priority","value":"P0"}]; also LLM-generated tool args that confuse the array-of-objects schema with array-of-strings.

Common situations: MCP clients/agents reformatting the schema; hand-written JSON tool payloads; passing a comma-separated string list split into tokens.

Related errors

• issue_fields must be an array
• field_name is required for each issue_fields item
• value cannot be null for field %q
• issue field %q cannot specify 'delete' together with 'value'
• issue field %q cannot specify both value and field_option_na

AI-assisted analysis of github/github-mcp-server@0ea1f775a7 (2026-08-15). Data as JSON: /api/errors/e7e7e0ef7823e3c5. Report an issue: GitHub.