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 on the cloud-sql-create-database tool asserts the bound source implements `compatibleSource`; if the assertion fails it returns this error. Only Cloud SQL sources that can provide the SQL admin service and create-database operation are permitted. The error means the tool was bound to an incompatible source kind.

Source

Thrown at internal/tools/cloudsql/cloudsqlcreatedatabase/cloudsqlcreatedatabase.go:100

}

// Tool represents the create-database 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)
	}
	instance, ok := paramsMap["instance"].(string)
	if !ok {

View on GitHub (pinned to 8cc6e09de2)

Solutions

  1. Point the tool's `source:` at a Cloud SQL source implementing compatibleSource (cloudsqlpg, cloudsqlmysql, cloudsqlmssql).
  2. Check the quoted source name and fix kind/name mismatches in the config.
  3. For custom sources, implement GetDefaultProject, GetService, UseClientAuthorization, and CreateDatabase.
  4. Reload config and verify startup validation succeeds.

Example fix

# before
tools:
  create-database:
    kind: cloud-sql-create-database
    source: pg-source

# after
tools:
  create-database:
    kind: cloud-sql-create-database
    source: cloudsql-pg-source
Defensive patterns

Strategy: validation

Validate before calling

// Go: fail fast at config load
if err := tool.ValidateSource(src); err != nil {
    log.Fatalf("create-database source invalid: %v", err)
}

Try / catch

if err := tool.ValidateSource(source); err != nil {
    return fmt.Errorf("cloud-sql-create-database bound to %T, expected a cloudsql* source: %w", source, err)
}

Prevention

When it happens

Trigger: Calling ValidateSource during tool/source binding with a sources.Source that does not implement the tool's compatibleSource interface — typically a `create-database` tool whose `source:` points at a non-Cloud-SQL source.

Common situations: tools.yml miswiring (postgres/mysql source named instead of cloudsql*); typos in source names; custom sources missing required methods; toolbox upgrades that expanded compatibleSource.

Related errors

AI-assisted analysis of googleapis/mcp-toolbox@8cc6e09de2 (2026-09-05). Data as JSON: /api/errors/6edf4b08b94ea6d2. Report an issue: GitHub.