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

Set the tool's `source` to a source of kind `mindsdb`

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

Tool.ValidateSource for mindsdb-sql rejects any source that does not implement the MindsDB compatibleSource interface. The tool cannot obtain a DB connection from an incompatible source, so the mismatch is surfaced as this error during tool/source validation.

Source

Thrown at internal/tools/mindsdb/mindsdbsql/mindsdbsql.go:104

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

Set the tool's `source` to a source of kind `mindsdb`
Cross-check `sources:` names against the tool's `source` field
Run a local toolbox start to validate every binding

Example fix

// before
source: my-bigquery
// after
source: my-mindsdb

Defensive patterns

Strategy: validation

Validate before calling

if err := mindsdbSQLTool.ValidateSource(src); err != nil {
    return fmt.Errorf("mindsdb-sql %q: %w", name, err)
}

Prevention

Only attach mindsdb-sql to MindsDB sources
Validate tool/source pairs at load time
Review diffs of tools.yaml for source field changes

When it happens

Trigger: Attaching a mindsdb-sql tool to a non-MindsDB source in tools.yaml; server startup calls ValidateSource for each tool/source pair.

Common situations: Wrong source reference in the tool config; source swapped to a different database kind; duplicated tool blocks where one kept an old source name.

Related errors

AI-assisted analysis of googleapis/mcp-toolbox@8cc6e09de2 (2026-09-05). Data as JSON: /api/errors/3a65ab87edf162bc. Report an issue: GitHub.