github/github-mcp-server · error

issue_fields must be an array

Error message

issue_fields must be an array

What it means

optionalIssueWriteFields (pkg/github/issues.go:253) type-switches the issue_fields argument. This error fires when issue_fields is present but is neither []any nor []map[string]any — i.e. the JSON value is a scalar, a single object, or null-shaped non-array. The field must be omitted entirely when unused, or an array of field-update objects.

Source

Thrown at pkg/github/issues.go:253

	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 {
			return nil, err
		}

		deleteField, _ := OptionalParam[bool](itemMap, "delete")
		value, hasValue := itemMap["value"]
		if hasValue && value == nil {
			return nil, fmt.Errorf("value cannot be null for field %q", fieldName)

View on GitHub (pinned to 0ea1f775a7)

Solutions

1. Wrap the value in an array: issue_fields=[{"field_name":"Priority",...}]
2. Omit issue_fields entirely when not updating fields
3. Validate the arg shape client-side against the tool schema before sending

Example fix

# before
{"issue_fields": {"field_name": "Priority", "value": "P0"}}

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

if raw, ok := args["issue_fields"]; ok {
    switch raw.(type) {
    case []any, []map[string]any:
        // ok
    default:
        return errors.New("issue_fields must be an array of objects")
    }
}

func isIssueFieldsArray(v any) bool {
    switch v.(type) {
    case []any, []map[string]any, nil:
        return true
    }
    return false
}

When it happens

Trigger: update_issue with issue_fields="Priority" (string), issue_fields={"field_name":"Priority"} (single object), or issue_fields=42. The type switch falls through to default and rejects the shape.

Common situations: Tool callers collapsing the array when updating a single field; LLMs emitting one object instead of a one-element array; config pipelines injecting strings.

Related errors

• each issue_fields item must be an object
• 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/dfbfde46ee558104. Report an issue: GitHub.