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

cloudsqlpg-create-instances accepts only Cloud SQL Postgres sources. ValidateSource type-asserts the bound sources.Source to compatibleSource and returns this error when the source is of any other kind, preventing the tool from invoking against an incompatible source.

Source

Thrown at internal/tools/cloudsqlpg/cloudsqlpgcreateinstances/cloudsqlpgcreateinstances.go:102

}

// Tool represents the create-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 {
		return nil, util.NewAgentError("missing 'project' parameter", nil)
	}
	name, ok := paramsMap["name"].(string)
	if !ok {

View on GitHub (pinned to 8cc6e09de2)

Solutions

  1. Point the tool at a `cloud-sql-postgres` source in the config
  2. Confirm the referenced source exists and is of the right kind (`toolbox --tools`)
  3. Use a generic run-sql tool instead if instance management isn't needed

Example fix

// before
source: my-postgres  # kind: postgres
// after
source: my-cloudsql-pg  # kind: cloud-sql-postgres
Defensive patterns

Strategy: validation

Validate before calling

if err := tool.ValidateSource(cfg.Sources[tool.Source]); err != nil { return fmt.Errorf("tool %q misconfigured: %w", tool.Name, err) }

Type guard

func isCloudSQLPgSource(s sources.Source) bool { _, ok := s.(interface{ GetDefaultProject() string }); return ok }

Try / catch

if err := tool.ValidateSource(src); err != nil {
    // fail config load; do not retry — this is a static config problem
    return err
}

Prevention

When it happens

Trigger: Tool initialization with `source.(compatibleSource)` failing — tool's `source` points at a non-cloud-sql-postgres source (plain `postgres`, `alloydb`, etc.).

Common situations: Reusing an alloydb or vanilla postgres source for instance creation; renaming sources and leaving stale references; prebuilt-config users overriding `source` incorrectly.

Related errors

AI-assisted analysis of googleapis/mcp-toolbox@8cc6e09de2 (2026-09-05). Data as JSON: /api/errors/ad26ee4fb5e20207. Report an issue: GitHub.