googleapis/mcp-toolbox · error

source is not compatible with the tool

Error message

source is not compatible with the tool

What it means

The bigtable-list-tables tool's ValidateSource returns this error when its compatibleSource assertion fails: the supplied source cannot list tables in a Bigtable instance. Because the toolbox wires tools to sources by name at runtime, only the concrete Bigtable source passes. The error is returned before any Bigtable API call, indicating a configuration mismatch.

Source

Thrown at internal/tools/bigtable/bigtablelisttables/bigtablelisttables.go:92

			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)
	}

	tables, err := source.ListTables(ctx)
	if err != nil {
		return nil, util.ProcessGcpError(err)
	}

View on GitHub (pinned to 8cc6e09de2)

Solutions

  1. Bind the tool to a source with kind: bigtable in the config
  2. Verify the source implements the tool's expected method set
  3. Align toolbox and source versions and rebuild the binary
  4. Validate tool-source pairings at startup and in CI

Example fix

// before
source: my-postgres-source
// after
source: my-bigtable-source
Defensive patterns

Strategy: validation

Validate before calling

if err := tool.ValidateSource(mySource); err != nil {
    return fmt.Errorf("bigtable-list-tables needs a bigtable source: %w", err)
}

Type guard

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

Try / catch

if err := tool.ValidateSource(src); err != nil {
    log.Fatalf("wrong source for bigtable-list-tables: %v", err)
}

Prevention

When it happens

Trigger: ValidateSource invoked, or the tool executed via the server, with a non-Bigtable source or a source lacking the required ListTables-style method for this toolbox version.

Common situations: tools.yaml references the wrong source for the tool; a source was renamed or its kind changed; custom source implementations not updated to the current interface after an upgrade.

Related errors

AI-assisted analysis of googleapis/mcp-toolbox@8cc6e09de2 (2026-09-05). Data as JSON: /api/errors/27489c30527cdfb8. Report an issue: GitHub.