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

Thrown by the bigtablesql Tool.ValidateSource when the sources.Source passed to the tool does not implement the compatibleSource interface expected by this tool. It catches wiring a tool to a source of the wrong kind at runtime before any query executes.

Source

Thrown at internal/tools/bigtable/bigtablesql/bigtablesql.go:106

// validate interface
var _ tools.Tool = 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
}

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()
	newStatement, err := parameters.ResolveTemplateParams(t.Cfg.TemplateParameters, t.Cfg.Statement, paramsMap)
	if err != nil {
		return nil, util.NewAgentError("unable to extract template params", err)
	}

	newParams, err := parameters.GetParams(t.Cfg.Parameters, paramsMap)
	if err != nil {
		return nil, util.NewAgentError("unable to extract standard params", err)

View on GitHub (pinned to 8cc6e09de2)

Solutions

  1. Set the tool's source field to a bigtable source kind in tools.yaml
  2. Verify the referenced source name exists and its kind initializes as a Bigtable-compatible source
  3. Rebuild/restart the toolbox so the new source-tool pairing is loaded
  4. If calling Invoke programmatically, pass the Source returned by the bigtable source's Initialize, not another source

Example fix

// before (tools.yaml)
sources:
  my-db:
    kind: postgres
    uri: ...
tools:
  execute-sql:
    kind: bigtable-sql
    source: my-db
// after
sources:
  my-bigtable:
    kind: bigtable
    project: my-project
    instance: my-instance
tools:
  execute-sql:
    kind: bigtable-sql
    source: my-bigtable
Defensive patterns

Strategy: type-guard

Validate before calling

// Before wiring the tool, assert the source implements the tool's interface
var _ sources.Source = mySource
if _, ok := mySource.(bigtablesql.CompatibleSource); !ok {
    return fmt.Errorf("source %s is not compatible with bigtable-sql", sourceName)
}

Type guard

func isCompatibleBigtableSQLSource(s sources.Source) (bigtablesql.CompatibleSource, bool) {
    cs, ok := s.(bigtablesql.CompatibleSource)
    return cs, ok
}

Prevention

When it happens

Trigger: Invoke/ValidateSource is called with a source whose concrete type does not satisfy bigtablesql's compatibleSource interface — e.g. the tool's source field points at a Postgres or non-Bigtable source in tools.yaml, or code passes the wrong Source into Invoke.

Common situations: Copy-pasting a tool block and leaving the source key pointing at a different database; renaming sources and forgetting to update the tool; programmatically constructing tool/source pairs mismatched after a config refactor.

Related errors

AI-assisted analysis of googleapis/mcp-toolbox@8cc6e09de2 (2026-09-05). Data as JSON: /api/errors/4c2330c6809503b8. Report an issue: GitHub.