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

The cloudstorage-get-bucket-iam-policy tool only works with sources that implement its compatibleSource interface (a Cloud Storage source). ValidateSource is called at server startup when binding a tool to a source; if the configured source is of a different type (e.g. a Postgres source), this error is returned. It catches YAML mistakes where a tool references the wrong source name.

Source

Thrown at internal/tools/cloudstorage/cloudstoragegetbucketiampolicy/cloudstoragegetbucketiampolicy.go:106

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)
	}
	mapParams := params.AsMap()
	bucket := cloudstoragecommon.ResolveString(t.Cfg.Bucket, mapParams, bucketKey)
	if bucket == "" {
		return nil, util.NewAgentError(fmt.Sprintf("invalid or missing '%s' parameter; expected a non-empty string", bucketKey), nil)
	}

	resp, err := source.GetBucketIAMPolicy(ctx, bucket)
	if err != nil {
		return nil, cloudstoragecommon.ProcessGCSError(err)

View on GitHub (pinned to 8cc6e09de2)

Solutions

1. Point the tool's `source` field at a cloudstorage source defined in the `sources` section.
2. Remove the tool if it was added to the wrong source's toolset.
3. Check the source name spelling against the keys under `sources:` in the config.

Example fix

# before
tools:
  get_bucket_iam_policy:
    kind: cloudstorage-get-bucket-iam-policy
    source: my-postgres
# after
tools:
  get_bucket_iam_policy:
    kind: cloudstorage-get-bucket-iam-policy
    source: my-gcs-source

if _, ok := src.(cloudstorage.CompatibleSource); !ok {
    return fmt.Errorf("tool %s requires a cloudstorage source", toolName)
}

func isCompatible(s sources.Source) bool { _, ok := s.(compatibleSource); return ok }

When it happens

Trigger: A tool config's `source` field names a source whose Go type does not implement the tool's compatibleSource interface — checked during ValidateSource at startup.

Common situations: Copy-pasted tool configs referencing the wrong source; renaming sources in YAML without updating tool bindings; mixing cloudstorage tools with database sources.

Related errors

• bucket cannot be empty for tool %q
• bucket cannot be empty for tool %q
• invalid source for %q tool: source %q is not a compatible ty
• bucket cannot be empty for tool %q
• invalid source for %q tool: source %q is not a compatible ty

AI-assisted analysis of googleapis/mcp-toolbox@8cc6e09de2 (2026-09-05). Data as JSON: /api/errors/ee597bff4c714a81. Report an issue: GitHub.