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

Tool.ValidateSource checks that the source instance passed to the tool implements the tool's compatibleSource interface (a MongoDB source). If the source wired to this mongodb-delete-one tool is any other type, validation fails with this message naming the tool type and the configured source name. It guards against misconfigured tool-to-source bindings before any DB call is made.

Source

Thrown at internal/tools/mongodb/mongodbdeleteone/mongodbdeleteone.go:121

// 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()

	collection, tbErr := mongodbcommon.ResolveCollection(t.Cfg.Collection, paramsMap)
	if tbErr != nil {
		return nil, tbErr
	}

	filterString, err := parameters.PopulateTemplateWithJSON("MongoDBDeleteOneFilter", t.Cfg.FilterPayload, paramsMap)
	if err != nil {

View on GitHub (pinned to 8cc6e09de2)

Solutions

  1. Set the tool's source to a MongoDB-based source kind (mongodb, mongodb-atlas, etc.).
  2. Confirm the referenced source name exists in the sources section and is of a MongoDB type.
  3. If composing sources programmatically, pass the *mongodb.Source (or compatible implementation) to the tool.

Example fix

# before
sources:
  my-pg:
    kind: postgres
    uri: postgres://...
tools:
  del:
    kind: mongodb-delete-one
    source: my-pg
# after
sources:
  my-mongo:
    kind: mongodb
    uri: mongodb://...
tools:
  del:
    kind: mongodb-delete-one
    source: my-mongo
Defensive patterns

Strategy: type-guard

Validate before calling

// Go: check compatibility before invoking
var src sources.Source = mySource
if _, ok := src.(mongodbdeleteonecompatibleSourcePlaceholder); !ok { /* use the tool's ValidateSource instead */ }
if err := tool.ValidateSource(mySource); err != nil { /* reconfigure */ }

Type guard

// Go: narrow to the MongoDB source family by checking kind
func isMongoSource(s sources.Source) bool {
    type mongoSrc interface{ SourceType() string }
    if m, ok := s.(mongoSrc); ok {
        t := m.SourceType()
        return t == "mongodb" || t == "mongodb-atlas"
    }
    return false
}

Try / catch

if err := t.ValidateSource(src); err != nil {
    return fmt.Errorf("source binding invalid, reconfigure tools.yaml: %w", err)
}

Prevention

When it happens

Trigger: A tools.yaml where a mongodb-delete-one tool references a source whose kind is not MongoDB (e.g. postgres, cloud-sql-postgres); programmatically passing a wrong sources.Source implementation to Invoke/ValidateSource.

Common situations: Copy-pasting tool definitions between configs and leaving the old source name; changing a source's kind without updating dependent tools; typos in source names that resolve to a different source.

Related errors

AI-assisted analysis of googleapis/mcp-toolbox@8cc6e09de2 (2026-09-05). Data as JSON: /api/errors/14e0f4d90b564ce0. Report an issue: GitHub.