What causes "tool type %q already registered" in googleapis/mcp-toolbox?

Search the codebase for "dataplex-create-data-asset" and eliminate the duplicate const.

tool type %q already registered

Error message

tool type %q already registered

What it means

This panic originates in init() of internal/tools/dataplex/dataplexcreatedataasset because tools.Register("dataplex-create-data-asset", newConfig) returned false, meaning the registry already holds that tool type key. The library fails fast at startup to prevent one tool definition from silently overwriting another. Resolution requires a unique registration per tool type.

Source

Thrown at internal/tools/dataplex/dataplexcreatedataasset/dataplexcreatedataasset.go:33

package dataplexcreatedataasset

import (
	"context"
	"fmt"
	"net/http"

	yaml "github.com/goccy/go-yaml"
	"github.com/googleapis/mcp-toolbox/internal/sources"
	"github.com/googleapis/mcp-toolbox/internal/tools"
	"github.com/googleapis/mcp-toolbox/internal/util"
	"github.com/googleapis/mcp-toolbox/internal/util/parameters"
)

const resourceType string = "dataplex-create-data-asset"

func init() {
	if !tools.Register(resourceType, newConfig) {
		panic(fmt.Sprintf("tool type %q already registered", resourceType))
	}
}

func newConfig(ctx context.Context, name string, decoder *yaml.Decoder) (tools.ToolConfig, error) {
	actual := Config{ConfigBase: tools.ConfigBase{Name: name}}
	if err := decoder.DecodeContext(ctx, &actual); err != nil {
		return nil, err
	}
	return actual, nil
}

type compatibleSource interface {
	CreateDataAsset(
		ctx context.Context,
		locationID string,
		dataProductID string,
		dataAssetID string,
		resourceURI string,

View on GitHub (pinned to 8cc6e09de2)

Solutions

Search the codebase for "dataplex-create-data-asset" and eliminate the duplicate const.
Give each tool package a unique resourceType per naming convention.
Deduplicate linked module copies so init runs once per package path.
Remove manual re-registration calls in tests.

Example fix

// before
const resourceType string = "dataplex-create-data-asset" // duplicate in another file
// after
const resourceType string = "dataplex-create-data-asset" // single source of truth; duplicate deleted

Defensive patterns

Strategy: validation

Validate before calling

const want = "dataplex-create-data-asset"
// uniqueness check before merge:
//   git grep -n 'dataplex-create-data-asset' -- '*.go'
// expect a single const resourceType declaration.

Try / catch

defer func() {
    if r := recover(); r != nil {
        if strings.Contains(fmt.Sprint(r), "already registered") {
            log.Fatalf("duplicate dataplex tool type: %v", r)
        }
        panic(r)
    }
}()

Prevention

Rename resourceType when copying sibling tool packages.
Run a CI grep/uniqueness test over all registered keys.
Restrict tools.Register calls to package init().
Prevent duplicate module copies via go mod tidy and pinned versions.
Boot the server in CI to catch registry panics before release.

When it happens

Trigger: Another declaration of the const "dataplex-create-data-asset" exists and its init() registers it too; or code (e.g., tests) calls tools.Register again for the same key after package initialization.

Common situations: Copy-paste of a sibling dataplex tool without renaming the const; merges bringing duplicate registrations; duplicate module/vendor copies; manual registration in test setup.

Related errors

AI-assisted analysis of googleapis/mcp-toolbox@8cc6e09de2 (2026-09-05). Data as JSON: /api/errors/bffb55980d817bb2. Report an issue: GitHub.