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

Bind the tool to a kind: cloudhealthcare source in tools.yaml.

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 for cloudhealthcare-get-dataset asserts the bound source implements the tool's compatibleSource interface (UseClientAuthorization and GetDataset per internal/tools/cloudhealthcare/cloudhealthcaregetdataset/cloudhealthcaregetdataset.go:46). Any other source type fails the assertion and produces this error. It is a wiring check performed when the tool is bound to a source.

Source

Thrown at internal/tools/cloudhealthcare/cloudhealthcaregetdataset/cloudhealthcaregetdataset.go:100

// 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)
	}
	var tokenStr string
	var err error
	if source.UseClientAuthorization() {
		tokenStr, err = accessToken.ParseBearerToken()
		if err != nil {
			return nil, util.NewClientServerError("error parsing access token", http.StatusUnauthorized, err)
		}
	}
	resp, err := source.GetDataset(tokenStr)

View on GitHub (pinned to 8cc6e09de2)

Solutions

Bind the tool to a kind: cloudhealthcare source in tools.yaml.
Fix the source name referenced by the tool.
Implement GetDataset(string) (*healthcare.Dataset, error) and UseClientAuthorization() bool on custom sources.
Rebuild so the concrete cloudhealthcare Source is registered.

Example fix

# before
source: my-spanner

# after
source: my-healthcare  # kind: cloudhealthcare

Defensive patterns

Strategy: type-guard

Validate before calling

if _, ok := src.(compatibleSource); !ok {
	return errors.New("cloudhealthcare-get-dataset requires a cloudhealthcare source (with GetDataset)")
}

Type guard

cs, ok := src.(compatibleSource)

Try / catch

if err := tool.ValidateSource(src); err != nil {
	log.Fatalf("bad tool/source binding: %v", err) // config bug, no retry
}

Prevention

Use kind: cloudhealthcare sources for cloudhealthcare tools.
Verify source references resolve to declared sources.
Make test doubles implement GetDataset and UseClientAuthorization.
Run go build after source refactors to catch interface breakage.

When it happens

Trigger: ValidateSource(source) is called with a source that is not the cloudhealthcare Source — e.g. a postgres/http source, or a stub missing GetDataset/UseClientAuthorization.

Common situations: tools.yaml binds the tool to a source of the wrong kind; a source-name typo; custom test doubles missing interface methods; refactor broke interface compliance.

Related errors

AI-assisted analysis of googleapis/mcp-toolbox@8cc6e09de2 (2026-09-05). Data as JSON: /api/errors/9b235ab4f0a7d841. Report an issue: GitHub.