googleapis/mcp-toolbox · error

limit must be a positive number, but got %d

Error message

limit must be a positive number, but got %d

What it means

The mongodb-find tool's Initialize validates that cfg.Limit is strictly positive, since MongoDB's find options require a positive limit and a zero/negative value is meaningless. A non-positive limit aborts tool initialization.

Source

Thrown at internal/tools/mongodb/mongodbfind/mongodbfind.go:96

func (cfg Config) Initialize(context.Context) (tools.Tool, error) {
	if cfg.Description == "" {
		return nil, fmt.Errorf("description is required for tool %q", cfg.Name)
	}

	allParameters := slices.Concat(cfg.FilterParams, cfg.ProjectParams, cfg.SortParams)

	if err := mongodbcommon.ValidateCollectionConfig(cfg.Collection, cfg.CollectionAllowedValues); err != nil {
		return nil, err
	}
	allParameters = mongodbcommon.WithRuntimeCollectionParam(cfg.Collection, cfg.CollectionAllowedValues, allParameters)

	if err := parameters.CheckDuplicateParameters(allParameters); err != nil {
		return nil, err
	}

	if cfg.Limit <= 0 {
		return nil, fmt.Errorf("limit must be a positive number, but got %d", cfg.Limit)
	}

	paramManifest := allParameters.Manifest()
	if paramManifest == nil {
		paramManifest = make([]parameters.ParameterManifest, 0)
	}

	return Tool{
		BaseTool: tools.NewBaseTool(
			cfg,
			tools.GetAnnotationsOrDefault(cfg.Annotations, tools.NewReadOnlyAnnotations),
			tools.Manifest{Description: cfg.Description, Parameters: paramManifest, AuthRequired: cfg.AuthRequired},
			allParameters,
		),
	}, nil
}

// validate interface

View on GitHub (pinned to 8cc6e09de2)

Solutions

1. Set limit to a positive integer in the tool config (e.g. limit: 10).
2. If unlimited results are desired, remove the limit field if supported, or use a large positive value.
3. Validate any dynamic limit value before placing it in the config.

Example fix

# before
  find-users:
    kind: mongodb-find
    source: my-mongo
    limit: 0
# after
  find-users:
    kind: mongodb-find
    source: my-mongo
    limit: 50

if cfg.Limit <= 0 {
    return errors.New("mongodb-find limit must be > 0")
}

func hasValidLimit(c mongodbfind.Config) bool { return c.Limit > 0 }

tool, err := cfg.Initialize(context.Background())
if err != nil && strings.Contains(err.Error(), "limit must be a positive number") {
    cfg.Limit = 10 // safe default
    tool, err = cfg.Initialize(context.Background())
}

When it happens

Trigger: Configuring a mongodb-find tool with limit: 0, a negative number, or omitting it in a way that leaves the field at 0 (or below) before Initialize runs.

Common situations: Setting limit to 0 believing it means 'unlimited'; copying configs where limit was left blank; computing limit from an env var or expression that evaluates to <= 0; integer type mismatch losing the value.

Understand the failure class

Background: "Must be a positive integer", "Invalid value", "Unsupported": the invalid-argument-value error family, when a library rejects the value you pass — this error's family across 35 libraries.

Related errors

• description is required for tool %q
• only one of 'collection' or 'collectionAllowedValues' can be
• description is required for tool %q
• description is required for tool %q
• description is required for tool %q

AI-assisted analysis of googleapis/mcp-toolbox@8cc6e09de2 (2026-09-05). Data as JSON: /api/errors/0486429aa6a90961. Report an issue: GitHub.