grafana/k6 · error · ErrMetricNameParsing

%w, metric %q has unmatched opening/close curly brace

Error message

%w, metric %q has unmatched opening/close curly brace

What it means

Raised by ParseMetricName when a metric name with tag filters contains only one of the '{' or '}' brace tokens, so the expression cannot be split into metric name and tag list. Wraps the ErrMetricNameParsing sentinel for use with errors.Is.

Source

Thrown at metrics/metric.go:106

// Its first return value is the parsed metric name, second are parsed tags as as slice
// of "key:value" strings. On failure, it returns an error containing the `ErrMetricNameParsing` in its chain.
func ParseMetricName(name string) (string, []string, error) {
	openingTokenPos := strings.IndexByte(name, '{')
	closingTokenPos := strings.LastIndexByte(name, '}')
	containsOpeningToken := openingTokenPos != -1
	containsClosingToken := closingTokenPos != -1

	// Neither the opening '{' token nor the closing '}' token
	// are present, thus the metric name only consists of a literal.
	if !containsOpeningToken && !containsClosingToken {
		return name, nil, nil
	}

	// If the name contains an opening or closing token, but not
	// its counterpart, the expression is malformed.
	if (containsOpeningToken && !containsClosingToken) ||
		(!containsOpeningToken && containsClosingToken) {
		return "", nil, fmt.Errorf(
			"%w, metric %q has unmatched opening/close curly brace",
			ErrMetricNameParsing, name,
		)
	}

	// If the closing brace token appears before the opening one,
	// the expression is malformed
	if closingTokenPos < openingTokenPos {
		return "", nil, fmt.Errorf("%w, metric %q closing curly brace appears before opening one", ErrMetricNameParsing, name)
	}

	// If the last character is not a closing brace token,
	// the expression is malformed.
	if closingTokenPos != (len(name) - 1) {
		err := fmt.Errorf(
			"%w, metric %q lacks a closing curly brace in its last position",
			ErrMetricNameParsing,
			name,

View on GitHub (pinned to 01ffac6f24)

Solutions

1. Balance the braces, e.g. http_req_duration{status:200}
2. Remove stray '{' or '}' characters from the metric name

When it happens

Trigger: Thrown at metrics/metric.go:106 when the library encounters an invalid state.

Common situations: See trigger scenarios.

AI-assisted analysis of grafana/k6@01ffac6f24 (2026-08-18). Data as JSON: /api/errors/b768003dc0d9b3ae. Report an issue: GitHub.