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 Dataplex source implementing GetDataProduct.

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 dataplexgetdataproduct tool's ValidateSource when the source passed in cannot be asserted to the tool's `compatibleSource` interface, i.e., it does not implement GetDataProduct with the expected signature. The tool only accepts sources capable of fetching a Dataplex data product, so any other source kind (or an incomplete implementation) is rejected with this message. It's a configuration/compatibility error surfaced before Invoke.

Source

Thrown at internal/tools/dataplex/dataplexgetdataproduct/dataplexgetdataproduct.go:101

// 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()
	locationID, ok := paramsMap["locationId"].(string)
	if !ok || locationID == "" {
		return nil, util.NewAgentError("locationId is required and must be a non-empty string", nil)
	}
	dataProductID, ok := paramsMap["dataProductId"].(string)
	if !ok || dataProductID == "" {
		return nil, util.NewAgentError("dataProductId is required and must be a non-empty string", nil)
	}

View on GitHub (pinned to 8cc6e09de2)

Solutions

Set the tool's `source` to a Dataplex source implementing GetDataProduct.
Check the compatibleSource interface at the top of internal/tools/dataplex/dataplexgetdataproduct/dataplexgetdataproduct.go and align your source's method set.
Implement the missing GetDataProduct method on custom sources with the exact interface signature.
Fix test fakes to embed the tool's compatibleSource interface.

Example fix

// before
// tools:
//   get-product:
//     kind: dataplex-get-data-product
//     source: mysql-source      # incompatible
//
// after
// tools:
//   get-product:
//     kind: dataplex-get-data-product
//     source: dataplex-source   # implements compatibleSource

Defensive patterns

Strategy: validation

Validate before calling

// At config load time, before running tools:
for name, tl := range loadedTools {
	if err := tl.Tool.(interface{ ValidateSource(sources.Source) error }).ValidateSource(loadedSources[tl.Source]); err != nil {
		return fmt.Errorf("tool %q: %w", name, err)
	}
}

Type guard

func isGetDataProductSource(s sources.Source) bool {
	_, ok := s.(interface {
		GetDataProduct(ctx context.Context, locationId, dataProductId string) (*dataplex.DataProduct, error)
	})
	return ok
}

Try / catch

if err := tool.ValidateSource(src); err != nil {
	switch {
	case strings.Contains(err.Error(), "not a compatible type"):
		return nil, fmt.Errorf("config error: tool requires a dataplex source: %w", err)
	default:
		return nil, err
	}
}

Prevention

Validate every tool/source pair when loading configuration, not at request time.
Match tool kind to source kind by convention (dataplex-* <-> dataplex).
Write table-driven tests pairing each tool with correct and incorrect sources.
Document required source kind in your tool config templates.

When it happens

Trigger: ValidateSource (or server startup wiring) receives a sources.Source whose concrete type is missing GetDataProduct(ctx, locationId, dataProductId) (*dataplex.DataProduct, error); typically from binding the tool to a wrong source in tools.yaml or using a stub in tests.

Common situations: Misconfigured tools.yaml where `source:` names a different database's source; custom source integrations that implement sources.Source but not the Dataplex-specific method; stale source implementations after a method rename; copy-paste of tool blocks without updating the source field.

Related errors

AI-assisted analysis of googleapis/mcp-toolbox@8cc6e09de2 (2026-09-05). Data as JSON: /api/errors/8f91270da370b69c. Report an issue: GitHub.