jaegertracing/jaeger · error

service_name is required

Error message

service_name is required

What it means

The get_span_names MCP handler requires a service name because span names are queried per service. When input.ServiceName is empty it cannot scope the query, so handle returns this sentinel error before calling the query service.

Source

Thrown at cmd/jaeger/internal/extension/jaegerquery/internal/mcptools/internal/handlers/get_span_names.go:53

// NewGetSpanNamesHandler creates a new get_span_names handler and returns the handler function.
func NewGetSpanNamesHandler(
	queryService *querysvc.QueryService,
) mcp.ToolHandlerFor[types.GetSpanNamesInput, types.GetSpanNamesOutput] {
	h := &getSpanNamesHandler{
		queryService: queryService,
	}
	return h.handle
}

// handle processes the get_span_names request.
func (h *getSpanNamesHandler) handle(
	ctx context.Context,
	_ *mcp.CallToolRequest,
	input types.GetSpanNamesInput,
) (*mcp.CallToolResult, types.GetSpanNamesOutput, error) {
	// Validate service name
	if input.ServiceName == "" {
		return nil, types.GetSpanNamesOutput{}, errors.New("service_name is required")
	}

	// Set default limit
	limit := input.Limit
	if limit <= 0 {
		limit = defaultSpanNameLimit
	}

	// Build query parameters
	// Normalize span kind to lowercase because storage backends store span kinds
	// in lowercase (e.g., "server") but the MCP schema documents uppercase examples
	// (e.g., "SERVER"). Without normalization, uppercase input silently returns
	// empty results instead of matching stored operations.
	query := tracestore.OperationQueryParams{
		ServiceName: input.ServiceName,
		SpanKind:    strings.ToLower(strings.TrimSpace(input.SpanKind)),
	}

View on GitHub (pinned to 806f444784)

Solutions

1. Fetch the available services via get_services and pass one as service_name
2. Validate service_name is non-empty in the caller before invoking the tool
3. Enforce the required field in the MCP tool input schema

Example fix

// before
out, err := spanNames.Handle(ctx, req, types.GetSpanNamesInput{})
// after
services, _ := getServices.Handle(ctx, req, types.GetServicesInput{})
out, err := spanNames.Handle(ctx, req, types.GetSpanNamesInput{ServiceName: services[0]})

if input.ServiceName == "" {
    return errors.New("service_name is required before calling get_span_names")
}

out, err := handler.Handle(ctx, req, input)
if err != nil && strings.Contains(err.Error(), "service_name is required") {
    return fmt.Errorf("call get_services first, then pass one service to get_span_names")
}

When it happens

Trigger: Calling the get_span_names MCP tool with ServiceName omitted or ""; often the caller skipped a prior get_services call and guessed no service.

Common situations: MCP client not enforcing required tool arguments; an LLM assuming span names are global rather than per-service; a UI dropdown left unselected.

Understand the failure class

Background: "missing required argument" and "the following required arguments were not provided": what required-argument errors mean and how to fix them — this error's family across 20 libraries.

Related errors

• trace_id is required
• trace_id is required
• trace_id is required
• start_time must be before end_time
• span_ids is required and must not be empty

AI-assisted analysis of jaegertracing/jaeger@806f444784 (2026-09-01). Data as JSON: /api/errors/bfe1d7a6ffde6848. Report an issue: GitHub.