grafana/k6 · error

invalid tag, empty string

Error message

invalid tag, empty string

What it means

The earliest sentinel in parseTagNameValue: the whole --tag argument is the empty string, before any '='-splitting is attempted. k6 cannot derive a name or value from an empty tag, so option parsing aborts with "error parsing tag ''". Distinct from empty-name (tag starts with '=') and empty-value (no '=' or trailing '=').

Source

Thrown at internal/cmd/options.go:20

import (
	"errors"
	"fmt"
	"strings"

	"github.com/spf13/pflag"
	"gopkg.in/guregu/null.v3"

	"go.k6.io/k6/v2/internal/build"
	"go.k6.io/k6/v2/lib"
	"go.k6.io/k6/v2/lib/types"
	"go.k6.io/k6/v2/metrics"
)

var (
	errTagEmptyName   = errors.New("invalid tag, empty name")
	errTagEmptyValue  = errors.New("invalid tag, empty value")
	errTagEmptyString = errors.New("invalid tag, empty string")
)

func optionFlagSet() *pflag.FlagSet {
	flags := pflag.NewFlagSet("", 0)
	flags.SortFlags = false

	flags.Int64P("vus", "u", 1, "number of virtual users")
	flags.DurationP("duration", "d", 0, "test duration limit")
	flags.Int64P("iterations", "i", 0, "script total iteration limit (among all VUs)")
	flags.StringSliceP("stage", "s", nil, "add a `stage`, as `[duration]:[target]`")
	flags.String("execution-segment", "", "limit execution to the specified segment, e.g. 10%, 1/3, 0.2:2/3")
	flags.String("execution-segment-sequence", "", "the execution segment sequence") // TODO better description
	flags.BoolP("paused", "p", false, "start the test in a paused state")
	flags.Bool("no-setup", false, "don't run setup()")
	flags.Bool("no-teardown", false, "don't run teardown()")
	flags.Int64("max-redirects", 10, "follow at most n redirects")
	flags.Int64("batch", 20, "max parallel batch reqs")
	flags.Int64("batch-per-host", 6, "max parallel batch reqs per host")

View on GitHub (pinned to 01ffac6f24)

Solutions

1. Remove the empty --tag argument or give it real content: --tag name=value
2. Build the flag conditionally: only append --tag "$TAG" when TAG is non-empty
3. Print the assembled command before executing to spot empty flag values

Example fix

# before
TAG=""
k6 run --tag "$TAG" script.js    # expands to --tag "" -> invalid tag, empty string

# after
TAG="${TAG:-}"
if [ -n "$TAG" ]; then k6 run --tag "$TAG" script.js; else k6 run script.js; fi

# build args conditionally so empty tag vars never reach k6
ARGS=()
[ -n "$TAG" ] && ARGS+=(--tag "$TAG")
k6 run "${ARGS[@]}" script.js

function isValidTag(s) {
  const i = s.indexOf('=');
  return i > 0 && i < s.length - 1;
}

When it happens

Trigger: Passing `--tag ""` explicitly, or far more often `--tag "$TAG"` where the TAG environment variable is unset or empty so the shell expands to an empty string; can also come from argument arrays built programmatically that append an empty element.

Common situations: CI pipelines conditionally adding tags where the condition produced an empty string; optional-tag logic that appends the flag unconditionally; typo'd env var names yielding empty expansion.

Related errors

• invalid tag, empty name
• invalid tag, empty value
• stack URL is required to validate token
• There were problems with the specified script configuration:
• empty name provided to SharedArray's constructor

AI-assisted analysis of grafana/k6@01ffac6f24 (2026-08-18). Data as JSON: /api/errors/df68930f4aec5b21. Report an issue: GitHub.