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

Point the tool at a cloud-logging-admin-compatible source.

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 for cloudloggingadmin-querylogs asserts the source implements compatibleSource to read UseClientAuthorization(). A source of any other Go type fails the assertion and produces this error, meaning the tool was bound to a non-Cloud Logging Admin source.

Source

Thrown at internal/tools/cloudloggingadmin/cloudloggingadminquerylogs/cloudloggingadminquerylogs.go:182

		Filter:      filter,
		NewestFirst: newestFirst,
		StartTime:   startTime,
		EndTime:     endTime,
		Verbose:     verbose,
		Limit:       limit,
	}

	resp, err := source.QueryLogs(ctx, queryParams, 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

Point the tool at a cloud-logging-admin-compatible source.
Add UseClientAuthorization() bool to custom source wrappers.
Validate config at startup to surface the mismatch early.

Example fix

// before
  query-logs:
    kind: cloud-logging-admin-query-logs
    source: my-postgres
// after
  query-logs:
    kind: cloud-logging-admin-query-logs
    source: my-logging-admin

Defensive patterns

Strategy: type-guard

Validate before calling

// Go: verify the source satisfies the tool's interface before use
if _, ok := src.(compatibleSource); !ok {
    return fmt.Errorf("query-logs tool requires a cloud-logging-admin source, got %T", src)
}

Type guard

func asCompatibleSource(s sources.Source) (compatibleSource, bool) {
    cs, ok := s.(compatibleSource)
    return cs, ok
}

Try / catch

ok, err := tool.RequiresClientAuthorization(src)
if err != nil {
    return fmt.Errorf("cannot resolve auth mode: %w", err)
}

Prevention

Compile-time assert custom sources: var _ compatibleSource = (*mySource)(nil).
Validate tool/source kind pairing during config load.
Keep tool bindings and sources sections edited together in the same PR.

When it happens

Trigger: Auth resolution during tool invocation or registration when tools.yaml binds querylogs to a database source or a custom source missing UseClientAuthorization().

Common situations: Wrong source name in tools.yaml; version upgrades that changed the source interface; custom source wrappers lacking the required method.

Related errors

AI-assisted analysis of googleapis/mcp-toolbox@8cc6e09de2 (2026-09-05). Data as JSON: /api/errors/e53f7bc6aa885654. Report an issue: GitHub.