googleapis/mcp-toolbox · error

invalid source for %q tool: source %q is not a compatible ty

Error message

invalid source for %q tool: source %q is not a compatible type

What it means

ValidateSource for alloydb-list-instances verifies the attached source implements compatibleSource (GetDefaultProject, UseClientAuthorization, ListInstance). Failing that, the tool cannot operate against the AlloyDB Admin API and this error is returned. It surfaces at tool/source wiring validation time.

Source

Thrown at internal/tools/alloydb/alloydblistinstances/alloydblistinstances.go:101

}

// Tool represents the list-instances tool.
type Tool struct {
	tools.BaseTool[Config]
}

func (t Tool) GetSourceName() string {
	return t.Cfg.Source
}

func (t Tool) ToConfig() tools.ToolConfig {
	return t.Cfg
}

func (t Tool) ValidateSource(source sources.Source) error {
	_, ok := source.(compatibleSource)
	if !ok {
		return fmt.Errorf("invalid source for %q tool: source %q is not a compatible type", t.Cfg.Type, t.Cfg.Source)
	}
	return nil
}

// Invoke executes the tool's logic.
func (t Tool) Invoke(ctx context.Context, s sources.Source, params parameters.ParamValues, accessToken tools.AccessToken) (any, util.ToolboxError) {
	source, ok := s.(compatibleSource)
	if !ok {
		return nil, util.NewClientServerError("source used is not compatible with the tool", http.StatusInternalServerError, nil)
	}
	paramsMap := params.AsMap()

	project, ok := paramsMap["project"].(string)
	if !ok || project == "" {
		return nil, util.NewAgentError("invalid or missing 'project' parameter; expected a string", nil)
	}
	location, ok := paramsMap["location"].(string)
	if !ok {

View on GitHub (pinned to 8cc6e09de2)

Solutions

  1. Set the tool's 'source' to an alloydb source name
  2. Confirm the source kind in the sources section of tools.yaml is alloydb
  3. Fix and re-validate the config before starting the server

Example fix

// before
source: my-bigquery
// after
source: my-alloydb
Defensive patterns

Strategy: validation

Validate before calling

if _, ok := source.(interface {
    GetDefaultProject() string
    UseClientAuthorization() bool
    ListInstance(context.Context, string, string, string) (any, error)
}); !ok {
    return fmt.Errorf("source %T incompatible with alloydb-list-instances", source)
}

Type guard

func isAlloyDBInstanceSource(s sources.Source) bool {
    _, ok := s.(alloydblistinstances.CompatibleSource)
    return ok
}

Prevention

When it happens

Trigger: ValidateSource called with any sources.Source other than the alloydb source — e.g. tools.yaml binds this tool to a postgres, mysql, or http source.

Common situations: Incorrect source reference in tools.yaml; copying tool definitions between source sections; refactoring source names without updating tool bindings.

Related errors

AI-assisted analysis of googleapis/mcp-toolbox@8cc6e09de2 (2026-09-05). Data as JSON: /api/errors/2a1093ae1e2966c0. Report an issue: GitHub.