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

Set the tool's source field to an AlloyDB (alloydb-admin style) source that implements the required interface.

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() type-asserts the provided sources.Source to the tool's compatibleSource interface. AlloyDB wait-for-operation only works with sources implementing its required methods (long-running operation polling against AlloyDB Admin API); any other source type fails validation with this message naming the tool type and configured source name.

Source

Thrown at internal/tools/alloydb/alloydbwaitforoperation/alloydbwaitforoperation.go:194

	// Polling configuration
	Delay      time.Duration
	MaxDelay   time.Duration
	Multiplier float64
	MaxRetries int
}

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)
	}
	location, ok := paramsMap["location"].(string)
	if !ok {

View on GitHub (pinned to 8cc6e09de2)

Solutions

Set the tool's source field to an AlloyDB (alloydb-admin style) source that implements the required interface.
Check the source definition in the sources: section of your config and confirm its type matches what this tool expects.
If you meant a different database, use the equivalent wait-for-operation tool for that source instead.

Example fix

// before
sources:
  my-alloydb:
    kind: postgres
tools:
  wait-op:
    kind: alloydb-wait-for-operation
    source: my-alloydb
// after
sources:
  my-alloydb:
    kind: alloydb-admin
tools:
  wait-op:
    kind: alloydb-wait-for-operation
    source: my-alloydb

Defensive patterns

Strategy: type-guard

Validate before calling

if _, ok := src.(sources.Source); !ok {
    return errors.New("value does not implement sources.Source")
}
// before attaching the tool, check the source kind in your config matches alloydb

Type guard

cs, ok := src.(alloydbwaitforoperation.CompatibleSource)
if !ok {
    return fmt.Errorf("source %T is not compatible with alloydb-wait-for-operation", src)
}

Try / catch

if err := tool.ValidateSource(src); err != nil {
    log.Fatalf("tool/source mismatch: %v", err)
}

Prevention

Keep tool-to-source bindings explicit and verified in your tools.yaml.
Call ValidateSource at startup and fail fast before serving traffic.
Avoid renaming sources without updating all tool references.
Use integration tests that initialize every configured tool against its source.

When it happens

Trigger: Attaching the alloydb-wait-for-operation tool to a source that does not implement compatibleSource — e.g. a postgres, cloud-sql, or storage source — either in YAML by pointing the tool's source field at an incompatible source, or programmatically by passing a wrong Source to ValidateSource.

Common situations: Copy-pasting a tool block between prebuilt configs and leaving the source pointing at the wrong database; renaming sources so the tool binds to the wrong one; mixing AlloyDB Admin tools with plain Postgres sources.

Related errors

AI-assisted analysis of googleapis/mcp-toolbox@8cc6e09de2 (2026-09-05). Data as JSON: /api/errors/d5b4b79029893b8d. Report an issue: GitHub.