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

Search the repository for "databaseinsights-get-index-recommendations" and eliminate the duplicate declaration.

tool type %q already registered

Error message

tool type %q already registered

What it means

This panic originates in init() of internal/tools/databaseinsights/getindexrecommendations: tools.Register(resourceType, newConfig) returned false because "databaseinsights-get-index-recommendations" was already registered in the global tool map. The library panics during program startup so a duplicate tool definition can never silently replace an existing one. Fixing it requires making the tool type key unique across the binary.

Source

Thrown at internal/tools/databaseinsights/getindexrecommendations/getindexrecommendations.go:35

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

	yaml "github.com/goccy/go-yaml"
	"github.com/googleapis/mcp-toolbox/internal/sources"
	"github.com/googleapis/mcp-toolbox/internal/sources/databaseinsights"
	"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 = "databaseinsights-get-index-recommendations"

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 {
	BatchQueryIndexRecommendations(ctx context.Context, req *databaseinsights.BatchQueryIndexRecommendationsRequest) (*databaseinsights.BatchQueryIndexRecommendationsResponse, error)
}

type Config struct {
	tools.ConfigBase `yaml:",inline"`
	Type             string                 `yaml:"type" validate:"required"`

View on GitHub (pinned to 8cc6e09de2)

Solutions

Search the repository for "databaseinsights-get-index-recommendations" and eliminate the duplicate declaration.
Assign a unique resourceType to each tool package per naming conventions.
Deduplicate module/vendor copies so the package is linked only once.
Remove manual tools.Register calls in tests that duplicate init-time registration.

Example fix

// before
const resourceType string = "databaseinsights-get-index-recommendations" // registered twice
// after
const resourceType string = "databaseinsights-index-recommendations" // or delete the duplicate package copy

Defensive patterns

Strategy: validation

Validate before calling

const want = "databaseinsights-get-index-recommendations"
// pre-merge check:
//   git grep -n 'databaseinsights-get-index-recommendations' -- '*.go'
// Expect exactly one declaration site plus its init() usage.

Try / catch

defer func() {
    if r := recover(); r != nil {
        if s, ok := r.(string); ok && strings.Contains(s, "already registered") {
            log.Fatalf("duplicate tool type: %s", s)
        }
        panic(r)
    }
}()

Prevention

Rename the resourceType whenever you fork or copy a tool package.
Verify with a repo-wide grep that the chosen key is unique before merging.
Register exclusively in init(); never re-register in tests.
Keep dependencies deduplicated so the package links once.
Add CI startup checks that fail the build on registry panics.

When it happens

Trigger: A duplicate resourceType constant exists elsewhere in the build and both init() functions call tools.Register; or custom/bootstrap code re-registers the same tool type after package initialization.

Common situations: Copy-pasted tool package with unchanged const; merge bringing two identical registrations; test scaffolding that re-runs registration; accidental duplicate import of the same package under two module versions.

Related errors

AI-assisted analysis of googleapis/mcp-toolbox@8cc6e09de2 (2026-09-05). Data as JSON: /api/errors/624b76c737dfe1eb. Report an issue: GitHub.