What causes "invalid source for %q tool: source %q is not a compatible type" in googleapis/mcp-toolbox?

Use a 'cloudhealthcare' kind source for this tool in tools.yaml.

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 asserts the incoming sources.Source to compatibleSource and returns this error when the tool is invoked or wired against a source that is not the Cloud Healthcare source. It is the upfront guard ensuring Invoke only ever sees a source exposing FHIR/DICOM store helpers.

Source

Thrown at internal/tools/cloudhealthcare/cloudhealthcaregetfhirstore/cloudhealthcaregetfhirstore.go:101

// validate interface
var _ tools.Tool = 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
}

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)
	}
	storeID, err := common.ValidateAndFetchStoreID(params, source.AllowedFHIRStores())
	if err != nil {
		return nil, util.NewAgentError("failed to validate store ID", err)
	}
	var tokenStr string
	if source.UseClientAuthorization() {
		tokenStr, err = accessToken.ParseBearerToken()
		if err != nil {
			return nil, util.NewClientServerError("error parsing access token", http.StatusUnauthorized, err)

View on GitHub (pinned to 8cc6e09de2)

Solutions

Use a 'cloudhealthcare' kind source for this tool in tools.yaml.
Confirm source registration: the source's SourceType() must equal the cloudhealthcare resource type.
Update mock sources in tests to implement compatibleSource.
Re-run toolbox init after upgrading to regenerate correct bindings.

Example fix

// before
  source: my-sql-source
// after
  source: my-healthcare-source

Defensive patterns

Strategy: type-guard

Validate before calling

if _, ok := src.(cloudhealthcare.Source); !ok {
    return errors.New("this tool only supports the cloudhealthcare source")
}

Type guard

func implementsCompatibleSource(s sources.Source) bool {
    _, ok := s.(interface {
        UseClientAuthorization() bool
        AllowedFHIRStores() []string
        IsFHIRStoreAllowed(string) bool
    })
    return ok
}

Try / catch

if err := tool.ValidateSource(src); err != nil {
    return fmt.Errorf("invalid source binding: %w", err)
}

Prevention

Bind healthcare tools only to healthcare sources
Run startup validation so ValidateSource fires before traffic
Update test doubles whenever compatibleSource gains methods
Keep source names unique to avoid accidental binding to the wrong entry

When it happens

Trigger: Invoke/ValidateSource called with a non-cloudhealthcare source, e.g. toolset assembly attaching this tool to a different engine's source.

Common situations: Wrong source referenced in tools.yaml; source kind renamed after an upgrade so binding resolves to the wrong source; test fakes not updated to the compatibleSource interface.

Related errors

AI-assisted analysis of googleapis/mcp-toolbox@8cc6e09de2 (2026-09-05). Data as JSON: /api/errors/dd6eefd9eb613b38. Report an issue: GitHub.