grafana/k6 · error

invalid tag, empty value

Error message

invalid tag, empty value

What it means

parseTagNameValue rejects --tag values with no '=' at all (idx == -1) or with '=' as the last character (idx == len-1): both mean the value side is empty. Every CLI tag must be a complete name=value pair; a bare name or a dangling 'name=' cannot form a metric tag.

Source

Thrown at internal/cmd/options.go:19

package cmd

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")

View on GitHub (pinned to 93accf6570)

Solutions

1. Write the full pair: --tag "env=prod"
2. If tag values come from variables, default or validate them so the '=' always has a right-hand side
3. Note that an intentionally empty value is not representable via this flag — choose a placeholder like 'unknown' if you need one

Example fix

# before
k6 run --tag "env" script.js        # ERR: invalid tag, empty value
k6 run --tag "env=" script.js       # ERR: invalid tag, empty value

# after
k6 run --tag "env=prod" script.js

# every tag must be a full name=value pair
for t in "${TAGS[@]}"; do
  case "$t" in
    *=?*) ;;      # name=value with non-empty value: OK
    *) echo "invalid tag '$t': expected name=value" >&2; exit 1 ;;
  esac
done

When it happens

Trigger: Running with --tag "env" (no '='), --tag "env=" (trailing '='), or the equivalent entries in K6_TAGS / repeated --tag flags where the value portion after the first '=' is empty.

Common situations: Forgetting the =value half when scripting --tag flags; a $TAG_VALUE variable that is empty so the shell produces "env="; assuming --tag works like a boolean flag; copying a tag list where the value was dropped.

Related errors

• invalid tag, empty name
• stack value is required but it was not passed or is empty
• 104
• the --local-execution flag is not compatible with the --exit
• the --local-execution flag is not compatible with the --show

AI-assisted analysis of grafana/k6@93accf6570 (2026-08-15). Data as JSON: /api/errors/9200ff44d5ace24a. Report an issue: GitHub.