What causes "source is not compatible with the tool" in googleapis/mcp-toolbox?

Set the tool's source field to a bigtable-kind source

source is not compatible with the tool

Error message

source is not compatible with the tool

What it means

bigtable-get-materialized-view's ValidateSource throws this when the provided source fails the type assertion against its compatibleSource interface (a GetMaterializedView(context.Context, string) (any, error) provider). The check exists because the tool depends on Bigtable-admin-specific functionality that only the Bigtable source implements. Any other source kind, or a stale source implementation, triggers it.

Source

Thrown at internal/tools/bigtable/bigtablegetmaterializedview/bigtablegetmaterializedview.go:95

			allParameters,
		),
	}, nil
}

var _ tools.Tool = Tool{}

type Tool struct {
	tools.BaseTool[Config]
}

func (t Tool) GetSourceName() string {
	return t.Cfg.Source
}

func (t Tool) ValidateSource(src sources.Source) error {
	_, ok := src.(compatibleSource)
	if !ok {
		return fmt.Errorf("source is not compatible with the tool")
	}
	return nil
}

func (t Tool) ToConfig() tools.ToolConfig {
	return t.Cfg
}

func (t Tool) Invoke(ctx context.Context, src sources.Source, params parameters.ParamValues, accessToken tools.AccessToken) (any, util.ToolboxError) {
	source, ok := src.(compatibleSource)
	if !ok {
		return nil, util.NewClientServerError("source used is not compatible with the tool", http.StatusInternalServerError, nil)
	}

	paramsMap := params.AsMap()

	res, err := source.GetMaterializedView(ctx, paramsMap["instance_id"].(string), paramsMap["materialized_view_id"].(string))
	if err != nil {

View on GitHub (pinned to 8cc6e09de2)

Solutions

Set the tool's source field to a bigtable-kind source
Ensure the source implements GetMaterializedView(context.Context, string) (any, error)
Sync toolbox and source versions; rebuild the binary
Validate the merged config at startup before serving requests

Example fix

// before
tools:
  get-mv:
    kind: bigtable-get-materialized-view
    source: postgres-prod
// after
tools:
  get-mv:
    kind: bigtable-get-materialized-view
    source: bigtable-prod

Defensive patterns

Strategy: validation

Validate before calling

if err := tool.ValidateSource(src); err != nil {
    return fmt.Errorf("bigtable-get-materialized-view requires a bigtable source: %w", err)
}

Type guard

func isBigtableMVSource(s sources.Source) bool {
    _, ok := s.(interface{ GetMaterializedView(context.Context, string) (any, error) })
    return ok
}

Try / catch

if err := tool.ValidateSource(src); err != nil {
    log.Fatalf("incompatible source for bigtable-get-materialized-view: %v", err)
}

Prevention

Only pair bigtable admin tools with kind: bigtable sources
Add a CI lint that checks tool kind vs source kind
Keep custom sources' method sets aligned with the toolbox version
Test tool registration locally before deploying

When it happens

Trigger: Calling ValidateSource or invoking the tool with a source that is not the Bigtable source, e.g. a SQL database source, or a Bigtable source build lacking the GetMaterializedView method.

Common situations: Miswired tools.yaml (tool referencing another engine's source); copy-paste of tool blocks without updating the source field; upgrading toolbox so a custom source no longer satisfies the interface.

Related errors

AI-assisted analysis of googleapis/mcp-toolbox@8cc6e09de2 (2026-09-05). Data as JSON: /api/errors/7e26381141966b34. Report an issue: GitHub.