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

RequiresClientAuthorization on the cloudloggingadmin-list-resource-types tool asserts the injected source implements compatibleSource so it can query UseClientAuthorization(). A source of an incompatible Go type makes the assertion fail and the method returns this error instead of a boolean. The tool cannot determine its auth behavior without the right source type.

Source

Thrown at internal/tools/cloudloggingadmin/cloudloggingadminlistresourcetypes/cloudloggingadminlistresourcetypes.go:112

	var err error
	if source.UseClientAuthorization() {
		tokenString, err = accessToken.ParseBearerToken()
		if err != nil {
			return nil, util.NewClientServerError("failed to parse access token", http.StatusUnauthorized, err)
		}
	}

	resp, err := source.ListResourceTypes(ctx, tokenString)
	if err != nil {
		return nil, util.ProcessGcpError(err)
	}
	return resp, nil
}

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

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

View on GitHub (pinned to 8cc6e09de2)

Solutions

  1. Bind the tool to a cloud-logging-admin source (one implementing compatibleSource).
  2. If using a custom source wrapper, add a UseClientAuthorization() bool method so it satisfies compatibleSource.
  3. Validate the config before serving so the mismatch surfaces at startup rather than during a request.

Example fix

// before (custom source)
type mySource struct{}
func (s mySource) SourceType() string { return "my-source" }
// after
type mySource struct{ UseClientAuth bool }
func (s mySource) SourceType() string { return "my-source" }
func (s mySource) UseClientAuthorization() bool { return s.UseClientAuth }
Defensive patterns

Strategy: type-guard

Validate before calling

// Go: assert source compatibility before invoking the tool
if _, ok := src.(compatibleSource); !ok {
    return false, fmt.Errorf("source %T does not support client authorization checks", src)
}

Type guard

func toCompatibleSource(s sources.Source) (compatibleSource, error) {
    if cs, ok := s.(compatibleSource); ok {
        return cs, nil
    }
    return nil, fmt.Errorf("incompatible source type %T", s)
}

Try / catch

useClientAuth, err := tool.RequiresClientAuthorization(src)
if err != nil {
    return fmt.Errorf("source binding invalid for tool %q: %w", tool.GetName(), err)
}

Prevention

When it happens

Trigger: Invoking the tool (server startup or per-call auth resolution) when the tool's configured source is not a Cloud Logging Admin-compatible source, e.g. a database source or a wrapped custom source missing UseClientAuthorization().

Common situations: Binding the tool to a source of the wrong kind in tools.yaml; custom sources implementing sources.Source but not the compatibleSource interface; refactors that changed the source's Go type after an upgrade.

Related errors

AI-assisted analysis of googleapis/mcp-toolbox@8cc6e09de2 (2026-09-05). Data as JSON: /api/errors/bd3b354806d55424. Report an issue: GitHub.