googleapis/mcp-toolbox · critical

tool type %q already registered

Error message

tool type %q already registered

What it means

This is a fail-fast panic raised during package initialization. The oceanbaseexecutesql package registers its factory under resourceType "oceanbase-execute-sql" in the global toolRegistry via tools.Register() (internal/tools/tools.go:43). When the registry map already holds that key (Register returns false), init() panics so duplicate tool-type claims are caught immediately at startup instead of one factory silently shadowing the other.

Source

Thrown at internal/tools/oceanbase/oceanbaseexecutesql/oceanbaseexecutesql.go:34

import (
	"context"
	"database/sql"
	"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 = "oceanbase-execute-sql"

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

type compatibleSource interface {
	OceanBasePool() *sql.DB
	RunSQL(context.Context, string, []any) (any, error)
}

type Config struct {
	tools.ConfigBase `yaml:",inline"`
	Type             string                 `yaml:"type" validate:"required"`
	Source           string                 `yaml:"source" validate:"required"`
	Annotations      *tools.ToolAnnotations `yaml:"annotations,omitempty"`
}

// validate interface
var _ tools.ToolConfig = Config{}

View on GitHub (pinned to 8cc6e09de2)

Solutions

  1. grep -rn 'oceanbase-execute-sql' to locate both registrations; assign the duplicate a unique resourceType.
  2. Remove the duplicate import or delete the obsolete package copy.
  3. Run go mod tidy and check replace directives / vendor for duplicates.
  4. Verify with `go build ./...` and `go test ./internal/tools/oceanbase/...`.

Example fix

// before
copied package: const resourceType string = "oceanbase-execute-sql"

// after
const resourceType string = "oceanbase-execute-sql-readonly" // unique to the new tool
Defensive patterns

Strategy: validation

Validate before calling

// Verify uniqueness before building:
// grep -rn '"oceanbase-execute-sql"' --include='*.go' . | grep 'resourceType\|tools.Register'
// Exactly one match expected. Soft guard for custom tools:
func init() {
	if !tools.Register(resourceType, newConfig) {
		fmt.Printf("WARNING: %s already registered; skipping duplicate init\n", resourceType)
		return
	}
}

Type guard

func isRegistered(resourceType string) bool {
	_, exists := registrySnapshot[resourceType]
	return exists
}

Try / catch

// Recover at the process boundary:
func main() {
	defer func() {
		if r := recover(); r != nil {
			if s, ok := r.(string); ok && strings.Contains(s, "already registered") {
				log.Fatalf("duplicate tool registration: %s", s)
			}
			panic(r)
		}
	}()
	rootCmd.Execute()
}

Prevention

When it happens

Trigger: Another init() calls tools.Register("oceanbase-execute-sql", ...): a copy of this package left after a rename, the package imported under two module paths (replace/fork/vendor), or a custom tool reusing this type string.

Common situations: Template-copying oceanbaseexecutesql for a new OceanBase tool and leaving the const unchanged; a rebase duplicating the package directory; two versions of the toolbox module both linked into the binary.

Related errors

AI-assisted analysis of googleapis/mcp-toolbox@8cc6e09de2 (2026-09-05). Data as JSON: /api/errors/1d42c9eaffe7dad0. Report an issue: GitHub.