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 neo4jcypher package registers its factory under resourceType "neo4j-cypher" in the global toolRegistry via tools.Register() (internal/tools/tools.go:43). A false return from Register() means the type string is already in the registry map, so init() panics rather than allowing a silent overwrite that would make YAML configs with `kind: neo4j-cypher` decode to the wrong tool.

Source

Thrown at internal/tools/neo4j/neo4jcypher/neo4jcypher.go:34

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

	"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 = "neo4j-cypher"

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 {
	Neo4jDatabase() string // kept to ensure neo4j source
	RunQuery(context.Context, string, map[string]any, bool, bool) (any, error)
}

type Config struct {
	tools.ConfigBase `yaml:",inline"`

View on GitHub (pinned to 8cc6e09de2)

Solutions

1. grep -rn '"neo4j-cypher"' to locate both registrations; give the duplicate a unique resourceType.
2. Remove the stale import or delete the obsolete package copy.
3. Deduplicate module copies (go mod tidy, fix replace directives).
4. Verify with `go build ./...` and `go test ./internal/tools/neo4j/...`.

Example fix

// before
const resourceType string = "neo4j-cypher" // in both original and copied package

// after
const resourceType string = "neo4j-cypher" // original only; new tool uses "neo4j-read-cypher"

// Verify uniqueness before building:
// grep -rn '"neo4j-cypher"' --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
	}
}

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

// 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()
}

When it happens

Trigger: Two init() functions register "neo4j-cypher": a duplicated/renamed copy of this package still using the constant, the package linked under two import paths (module replace/fork), or a new tool reusing the built-in type string.

Common situations: Copying neo4jcypher as a starting point for a variant Cypher tool and forgetting the const; a merge reintroducing an old package import; vendoring two versions of the toolbox module.

Related errors

• tool type %q already registered
• tool type %q already registered
• tool type %q already registered
• tool type %q already registered
• tool type %q already registered

AI-assisted analysis of googleapis/mcp-toolbox@8cc6e09de2 (2026-09-05). Data as JSON: /api/errors/0e7a50554afa44ed. Report an issue: GitHub.